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       flex, lex - fast lexical analyzer generator


       flex [-bcdfhilnpstvwBFILTV78+? -C[aefFmr] -ooutput -Pprefix -Sskeleton] [--help --version]
       [filename ...]


       This manual describes flex, a tool for generating programs that  perform  pattern-matching
       on text.  The manual includes both tutorial and reference sections:

               a brief overview of the tool

           Some Simple Examples

           Format Of The Input File

               the extended regular expressions used by flex

           How The Input Is Matched
               the rules for determining what has been matched

               how to specify what to do when a pattern is matched

           The Generated Scanner
               details regarding the scanner that flex produces;
               how to control the input source

           Start Conditions
               introducing context into your scanners, and
               managing "mini-scanners"

           Multiple Input Buffers
               how to manipulate multiple input sources; how to
               scan from strings instead of files

           End-of-file Rules
               special rules for matching the end of the input

           Miscellaneous Macros
               a summary of macros available to the actions

           Values Available To The User
               a summary of values available to the actions

           Interfacing With Yacc
               connecting flex scanners together with yacc parsers

               flex command-line options, and the "%option"

           Performance Considerations
               how to make your scanner go as fast as possible

           Generating C++ Scanners
               the (experimental) facility for generating C++
               scanner classes

           Incompatibilities With Lex And POSIX
               how flex differs from AT&T lex and the POSIX lex

               those error messages produced by flex (or scanners
               it generates) whose meanings might not be apparent

               files used by flex

           Deficiencies / Bugs
               known problems with flex

           See Also
               other documentation, related tools

               includes contact information


       flex is a tool for generating scanners: programs which recognize lexical patterns in text.
       flex reads the given input files, or its standard input if no file names are given, for  a
       description  of a scanner to generate.  The description is in the form of pairs of regular
       expressions and C code, called rules.  flex generates as output a C source file, lex.yy.c,
       which defines a routine yylex().  This file is compiled and linked with the -ll library to
       produce an executable.  When the executable is run, it analyzes its input for  occurrences
       of the regular expressions.  Whenever it finds one, it executes the corresponding C code.


       First  some  simple  examples  to get the flavor of how one uses flex.  The following flex
       input specifies a scanner which whenever it encounters the string "username" will  replace
       it with the user's login name:

           username    printf( "%s", getlogin() );

       By  default,  any  text  not matched by a flex scanner is copied to the output, so the net
       effect of this scanner is to copy its input file to its output  with  each  occurrence  of
       "username"  expanded.   In  this input, there is just one rule.  "username" is the pattern
       and the "printf" is the action.  The "%%" marks the beginning of the rules.

       Here's another simple example:

                   int num_lines = 0, num_chars = 0;

           \n      ++num_lines; ++num_chars;
           .       ++num_chars;

                   printf( "# of lines = %d, # of chars = %d\n",
                           num_lines, num_chars );

       This scanner counts the number of characters and the number of  lines  in  its  input  (it
       produces  no  output  other than the final report on the counts).  The first line declares
       two globals, "num_lines" and "num_chars", which are accessible both inside yylex() and  in
       the main() routine declared after the second "%%".  There are two rules, one which matches
       a newline ("\n") and increments both the line count and the character count, and one which
       matches any character other than a newline (indicated by the "." regular expression).

       A somewhat more complicated example:

           /* scanner for a toy Pascal-like language */

           /* need this for the call to atof() below */
           #include <math.h>

           DIGIT    [0-9]
           ID       [a-z][a-z0-9]*


           {DIGIT}+    {
                       printf( "An integer: %s (%d)\n", yytext,
                               atoi( yytext ) );

           {DIGIT}+"."{DIGIT}*        {
                       printf( "A float: %s (%g)\n", yytext,
                               atof( yytext ) );

           if|then|begin|end|procedure|function        {
                       printf( "A keyword: %s\n", yytext );

           {ID}        printf( "An identifier: %s\n", yytext );

           "+"|"-"|"*"|"/"   printf( "An operator: %s\n", yytext );

           "{"[^}\n]*"}"     /* eat up one-line comments */

           [ \t\n]+          /* eat up whitespace */

           .           printf( "Unrecognized character: %s\n", yytext );


           main( argc, argv )
           int argc;
           char **argv;
               ++argv, --argc;  /* skip over program name */
               if ( argc > 0 )
                       yyin = fopen( argv[0], "r" );
                       yyin = stdin;


       This  is  the  beginnings  of  a simple scanner for a language like Pascal.  It identifies
       different types of tokens and reports on what it has seen.

       The details of this example will be explained in the following sections.


       The flex input file consists of three sections, separated by a line with just %% in it:

           user code

       The definitions section contains declarations of simple name definitions to  simplify  the
       scanner  specification,  and  declarations  of  start conditions, which are explained in a
       later section.

       Name definitions have the form:

           name definition

       The "name" is a word beginning with a letter or an underscore ('_') followed  by  zero  or
       more  letters,  digits, '_', or '-' (dash).  The definition is taken to begin at the first
       non-white-space character following the name and continuing to the end of the  line.   The
       definition  can  subsequently  be  referred  to  using  "{name}",  which  will  expand  to
       "(definition)".  For example,

           DIGIT    [0-9]
           ID       [a-z][a-z0-9]*

       defines "DIGIT" to be a regular expression which matches a single digit, and "ID" to be  a
       regular  expression  which matches a letter followed by zero-or-more letters-or-digits.  A
       subsequent reference to


       is identical to


       and matches one-or-more digits followed by a '.' followed by zero-or-more digits.

       The rules section of the flex input contains a series of rules of the form:

           pattern   action

       where the pattern must be unindented and the action must begin on the same line.

       See below for a further description of patterns and actions.

       Finally, the user code section is simply copied to lex.yy.c  verbatim.   It  is  used  for
       companion  routines which call or are called by the scanner.  The presence of this section
       is optional; if it is missing, the second %% in the input file may be skipped, too.

       In the definitions and rules sections, any indented text or text enclosed in %{ and %}  is
       copied  verbatim to the output (with the %{}'s removed).  The %{}'s must appear unindented
       on lines by themselves.

       In the rules section, any indented or %{} text appearing before the first rule may be used
       to  declare variables which are local to the scanning routine and (after the declarations)
       code which is to be executed whenever the scanning routine is entered.  Other indented  or
       %{}  text  in the rule section is still copied to the output, but its meaning is not well-
       defined and it may well cause compile-time errors  (this  feature  is  present  for  POSIX
       compliance; see below for other such features).

       In  the definitions section (but not in the rules section), an unindented comment (i.e., a
       line beginning with "/*") is also copied verbatim to the output up to the next "*/".


       The patterns in the input are written using an extended set of regular expressions.  These

           x          match the character 'x'
           .          any character (byte) except newline
           [xyz]      a "character class"; in this case, the pattern
                        matches either an 'x', a 'y', or a 'z'
           [abj-oZ]   a "character class" with a range in it; matches
                        an 'a', a 'b', any letter from 'j' through 'o',
                        or a 'Z'
           [^A-Z]     a "negated character class", i.e., any character
                        but those in the class.  In this case, any
                        character EXCEPT an uppercase letter.
           [^A-Z\n]   any character EXCEPT an uppercase letter or
                        a newline
           r*         zero or more r's, where r is any regular expression
           r+         one or more r's
           r?         zero or one r's (that is, "an optional r")
           r{2,5}     anywhere from two to five r's
           r{2,}      two or more r's
           r{4}       exactly 4 r's
           {name}     the expansion of the "name" definition
                      (see above)
                      the literal string: [xyz]"foo
           \X         if X is an 'a', 'b', 'f', 'n', 'r', 't', or 'v',
                        then the ANSI-C interpretation of \x.
                        Otherwise, a literal 'X' (used to escape
                        operators such as '*')
           \0         a NUL character (ASCII code 0)
           \123       the character with octal value 123
           \x2a       the character with hexadecimal value 2a
           (r)        match an r; parentheses are used to override
                        precedence (see below)

           rs         the regular expression r followed by the
                        regular expression s; called "concatenation"

           r|s        either an r or an s

           r/s        an r but only if it is followed by an s.  The
                        text matched by s is included when determining
                        whether this rule is the "longest match",
                        but is then returned to the input before
                        the action is executed.  So the action only
                        sees the text matched by r.  This type
                        of pattern is called trailing context".
                        (There are some combinations of r/s that flex
                        cannot match correctly; see notes in the
                        Deficiencies / Bugs section below regarding
                        "dangerous trailing context".)
           ^r         an r, but only at the beginning of a line (i.e.,
                        when just starting to scan, or right after a
                        newline has been scanned).
           r$         an r, but only at the end of a line (i.e., just
                        before a newline).  Equivalent to "r/\n".

                      Note that flex's notion of "newline" is exactly
                      whatever the C compiler used to compile flex
                      interprets '\n' as; in particular, on some DOS
                      systems you must either filter out \r's in the
                      input yourself, or explicitly use r/\r\n for "r$".

           <s>r       an r, but only in start condition s (see
                        below for discussion of start conditions)
                      same, but in any of start conditions s1,
                        s2, or s3
           <*>r       an r in any start condition, even an exclusive one.

           <<EOF>>    an end-of-file
                      an end-of-file when in start condition s1 or s2

       Note that inside of a character class, all regular expression operators lose their special
       meaning except escape ('\') and the character class  operators,  '-',  ']',  and,  at  the
       beginning of the class, '^'.

       The  regular  expressions  listed  above are grouped according to precedence, from highest
       precedence at the top to  lowest  at  the  bottom.   Those  grouped  together  have  equal
       precedence.  For example,


       is the same as


       since  the '*' operator has higher precedence than concatenation, and concatenation higher
       than alternation ('|').  This pattern therefore matches either the  string  "foo"  or  the
       string "ba" followed by zero-or-more r's.  To match "foo" or zero-or-more "bar"'s, use:


       and to match zero-or-more "foo"'s-or-"bar"'s:


       In  addition  to  characters  and ranges of characters, character classes can also contain
       character class expressions.  These are expressions enclosed inside [: and  :]  delimiters
       (which  themselves  must  appear  between  the  '['  and ']' of the character class; other
       elements may occur inside the character class, too).  The valid expressions are:

           [:alnum:] [:alpha:] [:blank:]
           [:cntrl:] [:digit:] [:graph:]
           [:lower:] [:print:] [:punct:]
           [:space:] [:upper:] [:xdigit:]

       These expressions all designate a  set  of  characters  equivalent  to  the  corresponding
       standard  C  isXXX function.  For example, [:alnum:] designates those characters for which
       isalnum() returns true - i.e., any alphabetic or  numeric.   Some  systems  don't  provide
       isblank(), so flex defines [:blank:] as a blank or a tab.

       For example, the following character classes are all equivalent:


       If  your  scanner  is  case-insensitive  (the  -i  flag), then [:upper:] and [:lower:] are
       equivalent to [:alpha:].

       Some notes on patterns:

       -      A negated character class such as the example "[^A-Z]" above will match  a  newline
              unless  "\n" (or an equivalent escape sequence) is one of the characters explicitly
              present in the negated character class (e.g., "[^A-Z\n]").  This is unlike how many
              other  regular  expression tools treat negated character classes, but unfortunately
              the inconsistency is historically  entrenched.   Matching  newlines  means  that  a
              pattern  like  [^"]* can match the entire input unless there's another quote in the

       -      A rule can have at most one instance of trailing context (the '/' operator  or  the
              '$'  operator).  The start condition, '^', and "<<EOF>>" patterns can only occur at
              the beginning of a pattern, and, as well as with '/' and  '$',  cannot  be  grouped
              inside parentheses.  A '^' which does not occur at the beginning of a rule or a '$'
              which does not occur at the end of a rule  loses  its  special  properties  and  is
              treated as a normal character.

              The following are illegal:


              Note that the first of these, can be written "foo/bar\n".

              The following will result in '$' or '^' being treated as a normal character:


              If  what's wanted is a "foo" or a bar-followed-by-a-newline, the following could be
              used (the special '|' action is explained below):

                  foo      |
                  bar$     /* action goes here */

              A similar trick will work for matching a foo or a bar-at-the-beginning-of-a-line.


       When the generated scanner is run, it analyzes its input looking for strings  which  match
       any  of its patterns.  If it finds more than one match, it takes the one matching the most
       text (for trailing context rules, this includes the length  of  the  trailing  part,  even
       though  it  will  then  be returned to the input).  If it finds two or more matches of the
       same length, the rule listed first in the flex input file is chosen.

       Once the match is determined, the text corresponding to the match (called  the  token)  is
       made  available  in  the  global  character  pointer  yytext, and its length in the global
       integer yyleng.  The action corresponding to the matched pattern is then executed (a  more
       detailed  description  of  actions  follows),  and then the remaining input is scanned for
       another match.

       If no match is found, then the default rule is executed: the next character in  the  input
       is  considered  matched  and copied to the standard output.  Thus, the simplest legal flex
       input is:


       which generates a scanner that simply copies its input (one character at a  time)  to  its

       Note that yytext can be defined in two different ways: either as a character pointer or as
       a character array.  You can control which definition flex uses by  including  one  of  the
       special  directives  %pointer  or  %array  in the first (definitions) section of your flex
       input.  The default is %pointer, unless you use the -l lex compatibility option, in  which
       case  yytext  will  be  an array.  The advantage of using %pointer is substantially faster
       scanning and no buffer overflow when matching very large tokens (unless  you  run  out  of
       dynamic  memory).   The  disadvantage  is  that you are restricted in how your actions can
       modify yytext (see the next section), and calls  to  the  unput()  function  destroys  the
       present  contents  of  yytext,  which  can  be a considerable porting headache when moving
       between different lex versions.

       The advantage of %array is that you can then modify yytext to your  heart's  content,  and
       calls  to  unput()  do not destroy yytext (see below).  Furthermore, existing lex programs
       sometimes access yytext externally using declarations of the form:
           extern char yytext[];
       This definition is erroneous when used with %pointer, but correct for %array.

       %array defines yytext to be an array of YYLMAX characters,  which  defaults  to  a  fairly
       large value.  You can change the size by simply #define'ing YYLMAX to a different value in
       the first section of your flex input.  As mentioned  above,  with  %pointer  yytext  grows
       dynamically  to  accommodate  large  tokens.   While  this means your %pointer scanner can
       accommodate very large tokens (such as matching entire blocks of comments), bear  in  mind
       that  each  time  the scanner must resize yytext it also must rescan the entire token from
       the beginning, so matching  such  tokens  can  prove  slow.   yytext  presently  does  not
       dynamically grow if a call to unput() results in too much text being pushed back; instead,
       a run-time error results.

       Also note that you cannot use %array with C++ scanner classes (the c++ option; see below).


       Each pattern in a rule has a corresponding action, which can be any arbitrary C statement.
       The  pattern ends at the first non-escaped whitespace character; the remainder of the line
       is its action.  If the action is empty, then when the pattern is matched the  input  token
       is  simply  discarded.  For example, here is the specification for a program which deletes
       all occurrences of "zap me" from its input:

           "zap me"

       (It will copy all other characters in the input to the output since they will  be  matched
       by the default rule.)

       Here  is  a  program which compresses multiple blanks and tabs down to a single blank, and
       throws away whitespace found at the end of a line:

           [ \t]+        putchar( ' ' );
           [ \t]+$       /* ignore this token */

       If the action contains a '{', then the action spans till the balancing '}' is  found,  and
       the action may cross multiple lines.  flex knows about C strings and comments and won't be
       fooled by braces found within them, but also allows actions to  begin  with  %{  and  will
       consider  the  action  to be all the text up to the next %} (regardless of ordinary braces
       inside the action).

       An action consisting solely of a vertical bar ('|') means "same as the action for the next
       rule."  See below for an illustration.

       Actions  can  include  arbitrary  C code, including return statements to return a value to
       whatever routine called yylex().  Each time yylex()  is  called  it  continues  processing
       tokens from where it last left off until it either reaches the end of the file or executes
       a return.

       Actions are free to modify yytext except for lengthening  it  (adding  characters  to  its
       end--these  will  overwrite  later characters in the input stream).  This however does not
       apply when using %array (see above); in that case, yytext may be freely  modified  in  any

       Actions are free to modify yyleng except they should not do so if the action also includes
       use of yymore() (see below).

       There are a number of special directives which can be included within an action:

       -      ECHO copies yytext to the scanner's output.

       -      BEGIN followed by the  name  of  a  start  condition  places  the  scanner  in  the
              corresponding start condition (see below).

       -      REJECT  directs  the  scanner to proceed on to the "second best" rule which matched
              the input (or a prefix of the input).  The rule is chosen  as  described  above  in
              "How  the  Input  is  Matched", and yytext and yyleng set up appropriately.  It may
              either be one which matched as much text as the originally  chosen  rule  but  came
              later  in  the  flex  input file, or one which matched less text.  For example, the
              following will both count the words in the input and  call  the  routine  special()
              whenever "frob" is seen:

                          int word_count = 0;

                  frob        special(); REJECT;
                  [^ \t\n]+   ++word_count;

              Without  the REJECT, any "frob"'s in the input would not be counted as words, since
              the scanner normally executes only one action per  token.   Multiple  REJECT's  are
              allowed,  each  one finding the next best choice to the currently active rule.  For
              example, when  the  following  scanner  scans  the  token  "abcd",  it  will  write
              "abcdabcaba" to the output:

                  a        |
                  ab       |
                  abc      |
                  abcd     ECHO; REJECT;
                  .|\n     /* eat up any unmatched character */

              (The  first  three  rules  share the fourth's action since they use the special '|'
              action.)   REJECT  is  a  particularly  expensive  feature  in  terms  of   scanner
              performance; if it is used in any of the scanner's actions it will slow down all of
              the scanner's matching.  Furthermore, REJECT cannot be used with  the  -Cf  or  -CF
              options (see below).

              Note  also  that  unlike  the  other  special  actions,  REJECT  is  a branch; code
              immediately following it in the action will not be executed.

       -      yymore() tells the scanner that the next time it matches a rule, the  corresponding
              token should be appended onto the current value of yytext rather than replacing it.
              For example, given the input "mega-kludge" the  following  will  write  "mega-mega-
              kludge" to the output:

                  mega-    ECHO; yymore();
                  kludge   ECHO;

              First  "mega-"  is matched and echoed to the output.  Then "kludge" is matched, but
              the previous "mega-" is still hanging around at the beginning of yytext so the ECHO
              for the "kludge" rule will actually write "mega-kludge".

       Two  notes  regarding  use  of  yymore().   First, yymore() depends on the value of yyleng
       correctly reflecting the size of the current token, so you must not modify yyleng  if  you
       are  using  yymore().   Second, the presence of yymore() in the scanner's action entails a
       minor performance penalty in the scanner's matching speed.

       -      yyless(n) returns all but the first n characters of the current token back  to  the
              input  stream,  where  they  will  be rescanned when the scanner looks for the next
              match.  yytext and yyleng are adjusted appropriately  (e.g.,  yyleng  will  now  be
              equal  to  n  ).   For  example, on the input "foobar" the following will write out

                  foobar    ECHO; yyless(3);
                  [a-z]+    ECHO;

              An argument of 0 to yyless will cause the entire current input string to be scanned
              again.   Unless  you've changed how the scanner will subsequently process its input
              (using BEGIN, for example), this will result in an endless loop.

       Note that yyless is a macro and can only be used in the flex input file,  not  from  other
       source files.

       -      unput(c)  puts  the  character  c  back onto the input stream.  It will be the next
              character scanned.  The following action will take the current token and  cause  it
              to be rescanned enclosed in parentheses.

                  int i;
                  /* Copy yytext because unput() trashes yytext */
                  char *yycopy = strdup( yytext );
                  unput( ')' );
                  for ( i = yyleng - 1; i >= 0; --i )
                      unput( yycopy[i] );
                  unput( '(' );
                  free( yycopy );

              Note  that since each unput() puts the given character back at the beginning of the
              input stream, pushing back strings must be done back-to-front.

       An important potential problem when using unput() is that if you are using  %pointer  (the
       default),  a  call to unput() destroys the contents of yytext, starting with its rightmost
       character and devouring one character to the left with each call.  If you need  the  value
       of  yytext  preserved  after  a call to unput() (as in the above example), you must either
       first copy it elsewhere, or build your scanner using %array instead (see How The Input  Is

       Finally,  note  that  you  cannot put back EOF to attempt to mark the input stream with an

       -      input() reads the next character from the input stream.  For example, the following
              is one way to eat up C comments:

                  "/*"        {
                              int c;

                              for ( ; ; )
                                  while ( (c = input()) != '*' &&
                                          c != EOF )
                                      ;    /* eat up text of comment */

                                  if ( c == '*' )
                                      while ( (c = input()) == '*' )
                                      if ( c == '/' )
                                          break;    /* found the end */

                                  if ( c == EOF )
                                      error( "EOF in comment" );

              (Note  that  if the scanner is compiled using C++, then input() is instead referred
              to as yyinput(), in order to avoid a name clash with the C++ stream by the name  of

       -      YY_FLUSH_BUFFER  flushes  the  scanner's  internal buffer so that the next time the
              scanner attempts to match a token, it will first refill the buffer  using  YY_INPUT
              (see  The  Generated  Scanner,  below).   This action is a special case of the more
              general yy_flush_buffer() function, described below in the section  Multiple  Input

       -      yyterminate()  can  be  used  in  lieu  of  a  return  statement  in an action.  It
              terminates the scanner and returns a 0 to the  scanner's  caller,  indicating  "all
              done".    By   default,  yyterminate()  is  also  called  when  an  end-of-file  is
              encountered.  It is a macro and may be redefined.


       The output of flex is the file lex.yy.c, which contains the scanning  routine  yylex(),  a
       number  of  tables  used by it for matching tokens, and a number of auxiliary routines and
       macros.  By default, yylex() is declared as follows:

           int yylex()
               ... various definitions and the actions in here ...

       (If your environment supports function prototypes, then it will be "int yylex(  void  )".)
       This  definition  may  be changed by defining the "YY_DECL" macro.  For example, you could

           #define YY_DECL float lexscan( a, b ) float a, b;

       to give the scanning routine the name lexscan, returning a float, and taking two floats as
       arguments.  Note that if you give arguments to the scanning routine using a K&R-style/non-
       prototyped function declaration, you must terminate the definition with a semi-colon (;).

       Whenever yylex() is called, it scans  tokens  from  the  global  input  file  yyin  (which
       defaults  to  stdin).  It continues until it either reaches an end-of-file (at which point
       it returns the value 0) or one of its actions executes a return statement.

       If the scanner reaches an end-of-file, subsequent calls are undefined unless  either  yyin
       is  pointed  at  a  new  input  file (in which case scanning continues from that file), or
       yyrestart() is called.  yyrestart() takes one argument, a FILE *  pointer  (which  can  be
       nil,  if  you've  set  up YY_INPUT to scan from a source other than yyin), and initializes
       yyin for scanning from that  file.   Essentially  there  is  no  difference  between  just
       assigning  yyin to a new input file or using yyrestart() to do so; the latter is available
       for compatibility with previous versions of flex, and because it can  be  used  to  switch
       input  files  in  the  middle  of scanning.  It can also be used to throw away the current
       input buffer, by calling it with an argument of yyin; but better is to use YY_FLUSH_BUFFER
       (see  above).   Note  that  yyrestart() does not reset the start condition to INITIAL (see
       Start Conditions, below).

       If yylex() stops scanning due to executing a return statement in one of the  actions,  the
       scanner may then be called again and it will resume scanning where it left off.

       By  default  (and  for  purposes  of efficiency), the scanner uses block-reads rather than
       simple getc() calls to read characters from yyin.  The nature of how it gets its input can
       be   controlled   by   defining  the  YY_INPUT  macro.   YY_INPUT's  calling  sequence  is
       "YY_INPUT(buf,result,max_size)".  Its action is to place up to max_size characters in  the
       character  array  buf  and  return  in  the  integer  variable result either the number of
       characters read or the constant YY_NULL (0 on Unix systems) to indicate EOF.  The  default
       YY_INPUT reads from the global file-pointer "yyin".

       A sample definition of YY_INPUT (in the definitions section of the input file):

           #define YY_INPUT(buf,result,max_size) \
               { \
               int c = getchar(); \
               result = (c == EOF) ? YY_NULL : (buf[0] = c, 1); \

       This definition will change the input processing to occur one character at a time.

       When  the  scanner  receives  an  end-of-file indication from YY_INPUT, it then checks the
       yywrap() function.  If yywrap() returns false (zero), then it is assumed that the function
       has gone ahead and set up yyin to point to another input file, and scanning continues.  If
       it returns true (non-zero), then the scanner terminates, returning 0 to its caller.   Note
       that in either case, the start condition remains unchanged; it does not revert to INITIAL.

       If  you  do  not  supply  your  own  version of yywrap(), then you must either use %option
       noyywrap (in which case the scanner behaves as though yywrap() returned 1),  or  you  must
       link with -ll to obtain the default version of the routine, which always returns 1.

       Three  routines  are  available  for  scanning  from  in-memory buffers rather than files:
       yy_scan_string(), yy_scan_bytes(), and yy_scan_buffer().  See the discussion of them below
       in the section Multiple Input Buffers.

       The  scanner  writes  its  ECHO output to the yyout global (default, stdout), which may be
       redefined by the user simply by assigning it to some other FILE pointer.


       flex provides a mechanism for conditionally activating rules.  Any rule whose  pattern  is
       prefixed  with "<sc>" will only be active when the scanner is in the start condition named
       "sc".  For example,

           <STRING>[^"]*        { /* eat up the string body ... */

       will be active only when the scanner is in the "STRING" start condition, and

           <INITIAL,STRING,QUOTE>\.        { /* handle an escape ... */

       will be active only when the current start condition is  either  "INITIAL",  "STRING",  or

       Start  conditions  are  declared  in  the  definitions  (first) section of the input using
       unindented lines beginning with either %s or %x followed by a list of names.   The  former
       declares  inclusive  start  conditions,  the  latter  exclusive start conditions.  A start
       condition is activated using the BEGIN action.  Until the next BEGIN action  is  executed,
       rules  with the given start condition will be active and rules with other start conditions
       will be inactive.  If  the  start  condition  is  inclusive,  then  rules  with  no  start
       conditions at all will also be active.  If it is exclusive, then only rules qualified with
       the start condition will be active.  A set of rules contingent on the same exclusive start
       condition  describe  a  scanner which is independent of any of the other rules in the flex
       input.  Because of this, exclusive  start  conditions  make  it  easy  to  specify  "mini-
       scanners"  which scan portions of the input that are syntactically different from the rest
       (e.g., comments).

       If the distinction between inclusive and exclusive start  conditions  is  still  a  little
       vague,  here's  a  simple example illustrating the connection between the two.  The set of

           %s example

           <example>foo   do_something();

           bar            something_else();

       is equivalent to

           %x example

           <example>foo   do_something();

           <INITIAL,example>bar    something_else();

       Without the <INITIAL,example> qualifier, the bar pattern in the second example wouldn't be
       active  (i.e., couldn't match) when in start condition example.  If we just used <example>
       to qualify bar, though, then it would only be active in example and not in INITIAL,  while
       in  the  first example it's active in both, because in the first example the example start
       condition is an inclusive (%s) start condition.

       Also note that the special start-condition specifier <*> matches  every  start  condition.
       Thus, the above example could also have been written;

           %x example

           <example>foo   do_something();

           <*>bar    something_else();

       The default rule (to ECHO any unmatched character) remains active in start conditions.  It
       is equivalent to:

           <*>.|\n     ECHO;

       BEGIN(0) returns to the original state where only the rules with no start  conditions  are
       active.   This  state  can  also  be  referred  to  as  the  start-condition "INITIAL", so
       BEGIN(INITIAL) is equivalent to BEGIN(0).  (The parentheses  around  the  start  condition
       name are not required but are considered good style.)

       BEGIN  actions  can  also be given as indented code at the beginning of the rules section.
       For example, the following will cause the scanner to enter the "SPECIAL"  start  condition
       whenever yylex() is called and the global variable enter_special is true:

                   int enter_special;

           %x SPECIAL
                   if ( enter_special )

           ...more rules follow...

       To illustrate the uses of start conditions, here is a scanner which provides two different
       interpretations of a string like "123.456".  By default it will treat it as three  tokens,
       the  integer  "123",  a  dot  ('.'), and the integer "456".  But if the string is preceded
       earlier in the line by the string "expect-floats" it will treat it as a single token,  the
       floating-point number 123.456:

           #include <math.h>
           %s expect

           expect-floats        BEGIN(expect);

           <expect>[0-9]+"."[0-9]+      {
                       printf( "found a float, = %f\n",
                               atof( yytext ) );
           <expect>\n           {
                       /* that's the end of the line, so
                        * we need another "expect-number"
                        * before we'll recognize any more
                        * numbers

           [0-9]+      {
                       printf( "found an integer, = %d\n",
                               atoi( yytext ) );

           "."         printf( "found a dot\n" );

       Here  is a scanner which recognizes (and discards) C comments while maintaining a count of
       the current input line.

           %x comment
                   int line_num = 1;

           "/*"         BEGIN(comment);

           <comment>[^*\n]*        /* eat anything that's not a '*' */
           <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
           <comment>\n             ++line_num;
           <comment>"*"+"/"        BEGIN(INITIAL);

       This scanner goes to a bit of trouble to match as much text as possible  with  each  rule.
       In general, when attempting to write a high-speed scanner try to match as much possible in
       each rule, as it's a big win.

       Note that start-conditions names are really integer values and  can  be  stored  as  such.
       Thus, the above could be extended in the following fashion:

           %x comment foo
                   int line_num = 1;
                   int comment_caller;

           "/*"         {
                        comment_caller = INITIAL;


           <foo>"/*"    {
                        comment_caller = foo;

           <comment>[^*\n]*        /* eat anything that's not a '*' */
           <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
           <comment>\n             ++line_num;
           <comment>"*"+"/"        BEGIN(comment_caller);

       Furthermore,  you can access the current start condition using the integer-valued YY_START
       macro.  For example, the above assignments to comment_caller could instead be written

           comment_caller = YY_START;

       Flex provides YYSTATE as an alias for YY_START (since that is what's used by AT&T lex).

       Note that start conditions do not have their own name-space; %s's and %x's  declare  names
       in the same fashion as #define's.

       Finally,  here's  an  example of how to match C-style quoted strings using exclusive start
       conditions, including expanded escape sequences (but not including checking for  a  string
       that's too long):

           %x str

                   char string_buf[MAX_STR_CONST];
                   char *string_buf_ptr;

           \"      string_buf_ptr = string_buf; BEGIN(str);

           <str>\"        { /* saw closing quote - all done */
                   *string_buf_ptr = '\0';
                   /* return string constant token type and
                    * value to parser

           <str>\n        {
                   /* error - unterminated string constant */
                   /* generate error message */

           <str>\\[0-7]{1,3} {
                   /* octal escape sequence */
                   int result;

                   (void) sscanf( yytext + 1, "%o", &result );

                   if ( result > 0xff )
                           /* error, constant is out-of-bounds */

                   *string_buf_ptr++ = result;

           <str>\\[0-9]+ {
                   /* generate error - bad escape sequence; something
                    * like '\48' or '\0777777'

           <str>\\n  *string_buf_ptr++ = '\n';
           <str>\\t  *string_buf_ptr++ = '\t';
           <str>\\r  *string_buf_ptr++ = '\r';
           <str>\\b  *string_buf_ptr++ = '\b';
           <str>\\f  *string_buf_ptr++ = '\f';

           <str>\\(.|\n)  *string_buf_ptr++ = yytext[1];

           <str>[^\\\n\"]+        {
                   char *yptr = yytext;

                   while ( *yptr )
                           *string_buf_ptr++ = *yptr++;

       Often,  such  as in some of the examples above, you wind up writing a whole bunch of rules
       all preceded by the same start condition(s).  Flex makes this a little easier and  cleaner
       by introducing a notion of start condition scope.  A start condition scope is begun with:


       where  SCs  is  a list of one or more start conditions.  Inside the start condition scope,
       every rule automatically has the prefix <SCs> applied to it, until a '}' which matches the
       initial '{'.  So, for example,

               "\\n"   return '\n';
               "\\r"   return '\r';
               "\\f"   return '\f';
               "\\0"   return '\0';

       is equivalent to:

           <ESC>"\\n"  return '\n';
           <ESC>"\\r"  return '\r';
           <ESC>"\\f"  return '\f';
           <ESC>"\\0"  return '\0';

       Start condition scopes may be nested.

       Three routines are available for manipulating stacks of start conditions:

       void yy_push_state(int new_state)
              pushes  the  current  start condition onto the top of the start condition stack and
              switches to new_state as though you had used BEGIN  new_state  (recall  that  start
              condition names are also integers).

       void yy_pop_state()
              pops the top of the stack and switches to it via BEGIN.

       int yy_top_state()
              returns the top of the stack without altering the stack's contents.

       The  start  condition  stack grows dynamically and so has no built-in size limitation.  If
       memory is exhausted, program execution aborts.

       To use start condition stacks, your scanner must include a %option  stack  directive  (see
       Options below).


       Some  scanners  (such as those which support "include" files) require reading from several
       input streams.  As flex scanners do a large amount of buffering, one cannot control  where
       the  next  input  will be read from by simply writing a YY_INPUT which is sensitive to the
       scanning context.  YY_INPUT is only called when the scanner reaches the end of its buffer,
       which  may  be  a long time after scanning a statement such as an "include" which requires
       switching the input source.

       To negotiate these sorts of problems, flex provides a mechanism for creating and switching
       between multiple input buffers.  An input buffer is created by using:

           YY_BUFFER_STATE yy_create_buffer( FILE *file, int size )

       which  takes a FILE pointer and a size and creates a buffer associated with the given file
       and large enough to hold size characters (when in doubt, use YY_BUF_SIZE  for  the  size).
       It  returns  a  YY_BUFFER_STATE  handle,  which  may then be passed to other routines (see
       below).  The YY_BUFFER_STATE type  is  a  pointer  to  an  opaque  struct  yy_buffer_state
       structure, so you may safely initialize YY_BUFFER_STATE variables to ((YY_BUFFER_STATE) 0)
       if you wish, and also refer to the opaque structure in order to  correctly  declare  input
       buffers  in  source  files other than that of your scanner.  Note that the FILE pointer in
       the call to yy_create_buffer is only used as the value of yyin seen by  YY_INPUT;  if  you
       redefine  YY_INPUT  so it no longer uses yyin, then you can safely pass a nil FILE pointer
       to yy_create_buffer.  You select a particular buffer to scan from using:

           void yy_switch_to_buffer( YY_BUFFER_STATE new_buffer )

       switches the scanner's input buffer so subsequent tokens will come from new_buffer.   Note
       that  yy_switch_to_buffer()  may  be  used  by  yywrap()  to  set  things up for continued
       scanning, instead of opening a new file and pointing yyin at it.  Note also that switching
       input  sources  via  either  yy_switch_to_buffer()  or  yywrap() does not change the start

           void yy_delete_buffer( YY_BUFFER_STATE buffer )

       is used to reclaim the storage associated with a buffer.  ( buffer can be  nil,  in  which
       case  the  routine  does  nothing.)   You  can also clear the current contents of a buffer

           void yy_flush_buffer( YY_BUFFER_STATE buffer )

       This function discards the buffer's contents, so the next time  the  scanner  attempts  to
       match a token from the buffer, it will first fill the buffer anew using YY_INPUT.

       yy_new_buffer()  is  an  alias for yy_create_buffer(), provided for compatibility with the
       C++ use of new and delete for creating and destroying dynamic objects.

       Finally, the YY_CURRENT_BUFFER macro returns  a  YY_BUFFER_STATE  handle  to  the  current

       Here  is  an  example  of using these features for writing a scanner which expands include
       files (the <<EOF>> feature is discussed below):

           /* the "incl" state is used for picking up the name
            * of an include file
           %x incl

           #define MAX_INCLUDE_DEPTH 10
           YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH];
           int include_stack_ptr = 0;

           include             BEGIN(incl);

           [a-z]+              ECHO;
           [^a-z\n]*\n?        ECHO;

           <incl>[ \t]*      /* eat the whitespace */
           <incl>[^ \t\n]+   { /* got the include file name */
                   if ( include_stack_ptr >= MAX_INCLUDE_DEPTH )
                       fprintf( stderr, "Includes nested too deeply" );
                       exit( 1 );

                   include_stack[include_stack_ptr++] =

                   yyin = fopen( yytext, "r" );

                   if ( ! yyin )
                       error( ... );

                       yy_create_buffer( yyin, YY_BUF_SIZE ) );


           <<EOF>> {
                   if ( --include_stack_ptr < 0 )

                       yy_delete_buffer( YY_CURRENT_BUFFER );
                            include_stack[include_stack_ptr] );

       Three routines are available for setting up input buffers for scanning  in-memory  strings
       instead  of  files.   All  of  them create a new input buffer for scanning the string, and
       return  a  corresponding  YY_BUFFER_STATE   handle   (which   you   should   delete   with
       yy_delete_buffer()  when  done  with  it).   They  also  switch  to  the  new buffer using
       yy_switch_to_buffer(), so the next call to yylex() will start scanning the string.

       yy_scan_string(const char *str)
              scans a NUL-terminated string.

       yy_scan_bytes(const char *bytes, int len)
              scans len bytes (including possibly NUL's) starting at location bytes.

       Note that both of these functions create and scan a copy of the string  or  bytes.   (This
       may  be desirable, since yylex() modifies the contents of the buffer it is scanning.)  You
       can avoid the copy by using:

       yy_scan_buffer(char *base, yy_size_t size)
              which scans in place the buffer starting at base, consisting  of  size  bytes,  the
              last  two bytes of which must be YY_END_OF_BUFFER_CHAR (ASCII NUL).  These last two
              bytes are not scanned; thus, scanning consists  of  base[0]  through  base[size-2],

              If  you  fail  to  set  up  base  in  this  manner  (i.e.,  forget  the  final  two
              YY_END_OF_BUFFER_CHAR bytes), then yy_scan_buffer() returns a nil  pointer  instead
              of creating a new input buffer.

              The  type yy_size_t is an integral type to which you can cast an integer expression
              reflecting the size of the buffer.


       The special rule "<<EOF>>" indicates actions which are to be taken when an end-of-file  is
       encountered  and  yywrap() returns non-zero (i.e., indicates no further files to process).
       The action must finish by doing one of four things:

       -      assigning yyin to a new input file (in previous versions of flex, after  doing  the
              assignment  you  had  to  call  the  special  action YY_NEW_FILE; this is no longer

       -      executing a return statement;

       -      executing the special yyterminate() action;

       -      or, switching to a new buffer using yy_switch_to_buffer() as shown in  the  example

       <<EOF>>  rules may not be used with other patterns; they may only be qualified with a list
       of start conditions.  If an unqualified <<EOF>> rule is given, it  applies  to  all  start
       conditions which do not already have <<EOF>> actions.  To specify an <<EOF>> rule for only
       the initial start condition, use


       These rules are useful for catching things like unclosed comments.  An example:

           %x quote

           ...other rules for dealing with quotes...

           <quote><<EOF>>   {
                    error( "unterminated quote" );
           <<EOF>>  {
                    if ( *++filelist )
                        yyin = fopen( *filelist, "r" );


       The macro YY_USER_ACTION can be defined to provide an  action  which  is  always  executed
       prior  to the matched rule's action.  For example, it could be #define'd to call a routine
       to convert yytext to lower-case.  When YY_USER_ACTION  is  invoked,  the  variable  yy_act
       gives  the  number  of the matched rule (rules are numbered starting with 1).  Suppose you
       want to profile how often each of your rules is  matched.   The  following  would  do  the

           #define YY_USER_ACTION ++ctr[yy_act]

       where  ctr  is  an  array to hold the counts for the different rules.  Note that the macro
       YY_NUM_RULES gives the total number of rules (including the default rule, even if you  use
       -s), so a correct declaration for ctr is:

           int ctr[YY_NUM_RULES];

       The macro YY_USER_INIT may be defined to provide an action which is always executed before
       the first scan (and before the scanner's internal initializations are done).  For example,
       it could be used to call a routine to read in a data table or open a logging file.

       The  macro  yy_set_interactive(is_interactive)  can be used to control whether the current
       buffer is considered interactive.  An interactive buffer is  processed  more  slowly,  but
       must  be  used when the scanner's input source is indeed interactive to avoid problems due
       to waiting to fill buffers (see the discussion of the -I flag below).  A non-zero value in
       the  macro  invocation  marks  the buffer as interactive, a zero value as non-interactive.
       Note that use of this macro overrides %option interactive , %option always-interactive  or
       %option never-interactive (see Options below).  yy_set_interactive() must be invoked prior
       to beginning to scan the buffer that is (or is not) to be considered interactive.

       The macro yy_set_bol(at_bol) can be used to control whether the current buffer's  scanning
       context for the next token match is done as though at the beginning of a line.  A non-zero
       macro argument makes rules anchored with

       The macro YY_AT_BOL() returns true if the next token scanned from the current buffer  will
       have '^' rules active, false otherwise.

       In  the  generated scanner, the actions are all gathered in one large switch statement and
       separated using YY_BREAK, which may be redefined.  By default, it is simply a "break",  to
       separate  each  rule's  action from the following rule's.  Redefining YY_BREAK allows, for
       example, C++ users to #define YY_BREAK to do nothing (while being very careful that  every
       rule  ends  with  a  "break" or a "return"!) to avoid suffering from unreachable statement
       warnings where because a rule's action ends with "return", the YY_BREAK is inaccessible.


       This section summarizes the various values available to the user in the rule actions.

       -      char *yytext holds the text of the current token.   It  may  be  modified  but  not
              lengthened (you cannot append characters to the end).

              If  the  special  directive  %array  appears  in  the  first section of the scanner
              description, then yytext is instead declared char yytext[YYLMAX], where YYLMAX is a
              macro  definition  that you can redefine in the first section if you don't like the
              default value (generally 8KB).  Using %array results in somewhat  slower  scanners,
              but  the  value  of  yytext  becomes  immune to calls to input() and unput(), which
              potentially destroy its value when yytext is a character pointer.  The opposite  of
              %array is %pointer, which is the default.

              You cannot use %array when generating C++ scanner classes (the -+ flag).

       -      int yyleng holds the length of the current token.

       -      FILE  *yyin  is the file which by default flex reads from.  It may be redefined but
              doing so only makes  sense  before  scanning  begins  or  after  an  EOF  has  been
              encountered.   Changing  it  in  the midst of scanning will have unexpected results
              since flex buffers its input; use yyrestart() instead.   Once  scanning  terminates
              because an end-of-file has been seen, you can assign yyin at the new input file and
              then call the scanner again to continue scanning.

       -      void yyrestart( FILE *new_file ) may be called to point yyin at the new input file.
              The  switch-over  to the new file is immediate (any previously buffered-up input is
              lost).  Note that calling yyrestart() with yyin as an argument thus throws away the
              current input buffer and continues scanning the same input file.

       -      FILE  *yyout  is  the file to which ECHO actions are done.  It can be reassigned by
              the user.

       -      YY_CURRENT_BUFFER returns a YY_BUFFER_STATE handle to the current buffer.

       -      YY_START returns an integer value corresponding to  the  current  start  condition.
              You can subsequently use this value with BEGIN to return to that start condition.


       One of the main uses of flex is as a companion to the yacc parser-generator.  yacc parsers
       expect to call a routine named yylex() to find the  next  input  token.   The  routine  is
       supposed  to  return the type of the next token as well as putting any associated value in
       the global yylval.  To use flex with yacc, one specifies the -d option to yacc to instruct
       it to generate the file containing definitions of all the %tokens appearing in the
       yacc input.  This file is then included in the flex scanner.  For example, if one  of  the
       tokens is "TOK_NUMBER", part of the scanner might look like:

           #include ""


           [0-9]+        yylval = atoi( yytext ); return TOK_NUMBER;


       flex has the following options:

       -b, --backup
              Generate  backing-up  information  to lex.backup.  This is a list of scanner states
              which require backing up and the input characters on which they do so.   By  adding
              rules  one  can  remove backing-up states.  If all backing-up states are eliminated
              and -Cf or -CF is used, the generated scanner will run faster (see  the  -p  flag).
              Only  users  who  wish to squeeze every last cycle out of their scanners need worry
              about this option.  (See the section on Performance Considerations below.)

       -c     is a do-nothing, deprecated option included for POSIX compliance.

       -d, --debug
              makes the generated scanner run in debug mode.  Whenever a  pattern  is  recognized
              and  the  global yy_flex_debug is non-zero (which is the default), the scanner will
              write to stderr a line of the form:

                  --accepting rule at line 53 ("the matched text")

              The line number refers to the location of the rule in the file defining the scanner
              (i.e.,  the  file  that  was  fed  to  flex).  Messages are also generated when the
              scanner backs up, accepts the default rule, reaches the end of its input buffer (or
              encounters  a  NUL;  at  this  point, the two look the same as far as the scanner's
              concerned), or reaches an end-of-file.

       -f, --full
              specifies fast scanner.  No table compression is done and stdio is  bypassed.   The
              result is large but fast.  This option is equivalent to -Cfr (see below).

       -h, --help
              generates  a  "help"  summary  of flex's options to stdout and then exits.  -?  and
              --help are synonyms for -h.

       -i, --case-insensitive
              instructs flex to generate a case-insensitive scanner.  The case of  letters  given
              in the flex input patterns will be ignored, and tokens in the input will be matched
              regardless of case.  The matched text given in yytext will have the preserved  case
              (i.e., it will not be folded).

       -l, --lex-compat
              turns  on  maximum  compatibility  with the original AT&T lex implementation.  Note
              that  this  does  not  mean  full  compatibility.   Use  of  this  option  costs  a
              considerable amount of performance, and it cannot be used with the -+, -f, -F, -Cf,
              or -CF options.  For details on the compatibilities it provides,  see  the  section
              "Incompatibilities With Lex And POSIX" below.  This option also results in the name
              YY_FLEX_LEX_COMPAT being #define'd in the generated scanner.

       -n     is another do-nothing, deprecated option included only for POSIX compliance.

       -p, --perf-report
              generates a  performance  report  to  stderr.   The  report  consists  of  comments
              regarding  features  of  the  flex  input  file  which will cause a serious loss of
              performance in the resulting scanner.  If you give the flag twice,  you  will  also
              get comments regarding features that lead to minor performance losses.

              Note  that  the use of REJECT, %option yylineno, and variable trailing context (see
              the Deficiencies / Bugs section below) entails a substantial  performance  penalty;
              use  of  yymore(),  the  ^  operator,  and  the  -I  flag  entail minor performance

       -s, --no-default
              causes the default rule (that unmatched scanner input is echoed to  stdout)  to  be
              suppressed.   If the scanner encounters input that does not match any of its rules,
              it aborts with an error.  This option is useful for finding holes  in  a  scanner's
              rule set.

       -t, --stdout
              instructs  flex  to  write  the  scanner it generates to standard output instead of

       -v, --verbose
              specifies that flex should write to stderr a summary of  statistics  regarding  the
              scanner  it  generates.   Most of the statistics are meaningless to the casual flex
              user, but the first line identifies the version of flex (same as reported  by  -V),
              and  the next line the flags used when generating the scanner, including those that
              are on by default.

       -w, --nowarn
              suppresses warning messages.

       -B, --batch
              instructs flex to generate a batch scanner, the opposite  of  interactive  scanners
              generated by -I (see below).  In general, you use -B when you are certain that your
              scanner will never be used interactively, and you want to  squeeze  a  little  more
              performance  out  of  it.   If  your  goal  is  instead  to  squeeze out a lot more
              performance, you should be using the -Cf or -CF options  (discussed  below),  which
              turn on -B automatically anyway.

       -F, --fast
              specifies  that  the  fast  scanner  table representation should be used (and stdio
              bypassed).  This representation is about as fast as the full  table  representation
              (-f),  and  for some sets of patterns will be considerably smaller (and for others,
              larger).  In general, if the pattern set contains both "keywords" and a  catch-all,
              "identifier" rule, such as in the set:

                  "case"    return TOK_CASE;
                  "switch"  return TOK_SWITCH;
                  "default" return TOK_DEFAULT;
                  [a-z]+    return TOK_ID;

              then  you're  better  off  using  the  full  table  representation.   If  only  the
              "identifier" rule is present and you then use a hash table or some such  to  detect
              the keywords, you're better off using -F.

              This option is equivalent to -CFr (see below).  It cannot be used with -+.

       -I, --interactive
              instructs  flex  to generate an interactive scanner.  An interactive scanner is one
              that only looks ahead to decide what token has been matched if it absolutely  must.
              It turns out that always looking one extra character ahead, even if the scanner has
              already seen enough text to disambiguate the current token, is a  bit  faster  than
              only  looking  ahead  when  necessary.   But  scanners  that always look ahead give
              dreadful interactive performance; for example, when a user types a newline,  it  is
              not recognized as a newline token until they enter another token, which often means
              typing in another whole line.

              Flex scanners default  to  interactive  unless  you  use  the  -Cf  or  -CF  table-
              compression  options  (see  below).   That's  because  if  you're looking for high-
              performance you should be using one of  these  options,  so  if  you  didn't,  flex
              assumes  you'd  rather  trade  off  a  bit  of  run-time  performance for intuitive
              interactive behavior.  Note also that you cannot use -I in conjunction with -Cf  or
              -CF.   Thus,  this  option  is not really needed; it is on by default for all those
              cases in which it is allowed.

              Note that if isatty() returns false for the scanner  input,  flex  will  revert  to
              batch  mode,  even  if -I was specified.  To force interactive mode no matter what,
              use %option always-interactive (see Options below).

              You can force a scanner to not be interactive by using -B (see above).

       -L, --noline
              instructs flex not to generate #line directives.  Without this option, flex peppers
              the  generated  scanner with #line directives so error messages in the actions will
              be correctly located with respect to either the original flex input  file  (if  the
              errors  are  due  to code in the input file), or lex.yy.c (if the errors are flex's
              fault -- you should report these sorts of errors to the email address given below).

       -T, --trace
              makes flex run in trace mode.  It  will  generate  a  lot  of  messages  to  stderr
              concerning   the  form  of  the  input  and  the  resultant  non-deterministic  and
              deterministic finite automata.  This option is mostly for use in maintaining flex.

       -V, --version
              prints the version number to stdout and exits.  --version is a synonym for -V.

       -7, --7bit
              instructs flex to generate a 7-bit scanner, i.e.,  one  which  can  only  recognize
              7-bit  characters  in  its  input.  The advantage of using -7 is that the scanner's
              tables can be up to half the size of those  generated  using  the  -8  option  (see
              below).   The disadvantage is that such scanners often hang or crash if their input
              contains an 8-bit character.

              Note, however, that unless you generate your scanner using the  -Cf  or  -CF  table
              compression  options,  use  of -7 will save only a small amount of table space, and
              make your scanner considerably  less  portable.   Flex's  default  behavior  is  to
              generate  an  8-bit  scanner  unless  you  use  the  -Cf or -CF, in which case flex
              defaults to generating 7-bit scanners unless your site  was  always  configured  to
              generate  8-bit  scanners  (as will often be the case with non-USA sites).  You can
              tell whether flex generated a 7-bit or an 8-bit  scanner  by  inspecting  the  flag
              summary in the -v output as described above.

              Note  that if you use -Cfe or -CFe (those table compression options, but also using
              equivalence classes as discussed see below), flex still defaults to  generating  an
              8-bit  scanner,  since usually with these compression options full 8-bit tables are
              not much more expensive than 7-bit tables.

       -8, --8bit
              instructs flex to generate an 8-bit scanner, i.e., one which  can  recognize  8-bit
              characters.   This  flag is only needed for scanners generated using -Cf or -CF, as
              otherwise flex defaults to generating an 8-bit scanner anyway.

              See the discussion of -7 above  for  flex's  default  behavior  and  the  tradeoffs
              between 7-bit and 8-bit scanners.

       -+, --c++
              specifies  that  you want flex to generate a C++ scanner class.  See the section on
              Generating C++ Scanners below for details.

              controls the degree of table compression and, more  generally,  trade-offs  between
              small scanners and fast scanners.

              -Ca,  --align  ("align") instructs flex to trade off larger tables in the generated
              scanner for faster performance because  the  elements  of  the  tables  are  better
              aligned  for  memory  access and computation.  On some RISC architectures, fetching
              and manipulating longwords is more efficient than with smaller-sized units such  as
              shortwords.  This option can double the size of the tables used by your scanner.

              -Ce,  --ecs directs flex to construct equivalence classes, i.e., sets of characters
              which have identical lexical properties (for example, if  the  only  appearance  of
              digits  in  the  flex  input is in the character class "[0-9]" then the digits '0',
              '1', ..., '9' will all be put in the same equivalence class).  Equivalence  classes
              usually  give dramatic reductions in the final table/object file sizes (typically a
              factor of 2-5) and  are  pretty  cheap  performance-wise  (one  array  look-up  per
              character scanned).

              -Cf  specifies  that  the full scanner tables should be generated - flex should not
              compress the tables by  taking  advantages  of  similar  transition  functions  for
              different states.

              -CF  specifies  that  the  alternative fast scanner representation (described above
              under the -F flag) should be used.  This option cannot be used with -+.

              -Cm, --meta-ecs directs flex to construct meta-equivalence classes, which are  sets
              of  equivalence  classes (or characters, if equivalence classes are not being used)
              that are commonly used together.  Meta-equivalence classes are often a big win when
              using  compressed  tables,  but they have a moderate performance impact (one or two
              "if" tests and one array look-up per character scanned).

              -Cr, --read causes the generated scanner to bypass use of the standard I/O  library
              (stdio)  for input.  Instead of calling fread() or getc(), the scanner will use the
              read() system call, resulting in a performance gain which  varies  from  system  to
              system, but in general is probably negligible unless you are also using -Cf or -CF.
              Using -Cr can cause strange behavior if, for example,  you  read  from  yyin  using
              stdio  prior  to  calling  the scanner (because the scanner will miss whatever text
              your previous reads left in the stdio input buffer).

              -Cr has no effect if you define YY_INPUT (see The Generated Scanner above).

              A lone -C specifies that the  scanner  tables  should  be  compressed  but  neither
              equivalence classes nor meta-equivalence classes should be used.

              The options -Cf or -CF and -Cm do not make sense together - there is no opportunity
              for meta-equivalence classes if the table is not being compressed.   Otherwise  the
              options may be freely mixed, and are cumulative.

              The  default setting is -Cem, which specifies that flex should generate equivalence
              classes and meta-equivalence classes.  This setting provides the highest degree  of
              table  compression.   You  can  trade  off faster-executing scanners at the cost of
              larger tables with the following generally being true:

                  slowest & smallest
                  fastest & largest

              Note that scanners with the smallest tables are usually generated and compiled  the
              quickest,  so  during development you will usually want to use the default, maximal

              -Cfe is often a good compromise between speed and size for production scanners.

       -ooutput, --outputfile=FILE
              directs flex to write the scanner to the file output instead of lex.yy.c.   If  you
              combine  -o with the -t option, then the scanner is written to stdout but its #line
              directives (see the -L option above) refer to the file output.

       -Pprefix, --prefix=STRING
              changes the default yy prefix used by flex for all  globally-visible  variable  and
              function names to instead be prefix.  For example, -Pfoo changes the name of yytext
              to footext.  It also changes the name of the default output file from  lex.yy.c  to
      Here are all of the names affected:


              (If  you  are  using a C++ scanner, then only yywrap and yyFlexLexer are affected.)
              Within your scanner itself, you  can  still  refer  to  the  global  variables  and
              functions  using  either  version  of  their  name;  but  externally, they have the
              modified name.

              This option lets you easily link together multiple  flex  programs  into  the  same
              executable.  Note, though, that using this option also renames yywrap(), so you now
              must either provide your own (appropriately-named) version of the routine for  your
              scanner,  or  use  %option noyywrap, as linking with -ll no longer provides one for
              you by default.

       -Sskeleton_file, --skel=FILE
              overrides the default skeleton  file  from  which  flex  constructs  its  scanners.
              You'll never need this option unless you are doing flex maintenance or development.

       -X, --posix-compat
              maximal compatibility with POSIX lex.

              track line count in yylineno.

              name of C++ class.

              create a C header file in addition to the scanner.

              write tables to FILE.

              #define macro defn (default defn is '1').

       -R, --reentrant
              generate a reentrant C scanner

              scanner for bison pure parser.

              include yylloc support.

              initialize yyin/yyout to stdin/stdout.

       --noansi-definitions old-style function definitions.

              empty parameter list in prototypes.

              do not include <unistd.h>.

              do not generate a particular FUNCTION.

       flex  also  provides  a mechanism for controlling options within the scanner specification
       itself, rather than from the  flex  command-line.   This  is  done  by  including  %option
       directives  in  the  first section of the scanner specification.  You can specify multiple
       options with a single %option directive, and multiple directives in the first  section  of
       your flex input file.

       Most  options  are  given  simply  as names, optionally preceded by the word "no" (with no
       intervening whitespace) to negate their meaning.  A number are equivalent to flex flags or
       their negation:

           7bit            -7 option
           8bit            -8 option
           align           -Ca option
           backup          -b option
           batch           -B option
           c++             -+ option

           caseful or
           case-sensitive  opposite of -i (default)

           case-insensitive or
           caseless        -i option

           debug           -d option
           default         opposite of -s option
           ecs             -Ce option
           fast            -F option
           full            -f option
           interactive     -I option
           lex-compat      -l option
           meta-ecs        -Cm option
           perf-report     -p option
           read            -Cr option
           stdout          -t option
           verbose         -v option
           warn            opposite of -w option
                           (use "%option nowarn" for -w)

           array           equivalent to "%array"
           pointer         equivalent to "%pointer" (default)

       Some %option's provide features otherwise not available:

              instructs   flex   to   generate   a  scanner  which  always  considers  its  input
              "interactive".  Normally, on each new input file the scanner calls isatty()  in  an
              attempt  to  determine  whether  the scanner's input source is interactive and thus
              should be read a character at a time.  When this option is used, however,  then  no
              such call is made.

       main   directs  flex  to  provide  a  default main() program for the scanner, which simply
              calls yylex().  This option implies noyywrap (see below).

              instructs flex to generate a scanner which never considers its input  "interactive"
              (again, no call made to isatty()).  This is the opposite of always-interactive.

       stack  enables the use of start condition stacks (see Start Conditions above).

              if  set  (i.e.,  %option  stdinit)  initializes yyin and yyout to stdin and stdout,
              instead of the default of nil.  Some existing lex programs depend on this behavior,
              even  though  it  is  not  compliant  with ANSI C, which does not require stdin and
              stdout to be compile-time constant.

              directs flex to generate a scanner that maintains the number of  the  current  line
              read  from  its  input  in the global variable yylineno.  This option is implied by
              %option lex-compat.

       yywrap if unset (i.e., %option noyywrap), makes the scanner not call yywrap() upon an end-
              of-file,  but  simply  assume  that there are no more files to scan (until the user
              points yyin at a new file and calls yylex() again).

       flex scans your rule actions to determine whether you use the REJECT or yymore() features.
       The reject and yymore options are available to override its decision as to whether you use
       the options, either by setting them (e.g., %option reject)  to  indicate  the  feature  is
       indeed  used,  or  unsetting  them  to  indicate  it  actually  is not used (e.g., %option

       Three options take string-delimited values, offset with '=':

           %option outfile="ABC"

       is equivalent to -oABC, and

           %option prefix="XYZ"

       is equivalent to -PXYZ.  Finally,

           %option yyclass="foo"

       only applies when generating a C++ scanner ( -+ option).  It informs flex  that  you  have
       derived  foo  as  a subclass of yyFlexLexer, so flex will place your actions in the member
       function  foo::yylex()   instead   of   yyFlexLexer::yylex().    It   also   generates   a
       yyFlexLexer::yylex()   member   function   that   emits  a  run-time  error  (by  invoking
       yyFlexLexer::LexerError()) if called.  See Generating C++ Scanners, below, for  additional

       A  number of options are available for lint purists who want to suppress the appearance of
       unneeded routines in the generated scanner.   Each  of  the  following,  if  unset  (e.g.,
       %option  nounput  ),  results  in the corresponding routine not appearing in the generated

           input, unput
           yy_push_state, yy_pop_state, yy_top_state
           yy_scan_buffer, yy_scan_bytes, yy_scan_string

       (though yy_push_state() and friends won't appear anyway unless you use %option stack).


       The main design goal of flex is that it generate high-performance scanners.  It  has  been
       optimized  for  dealing  well with large sets of rules.  Aside from the effects on scanner
       speed of the  table  compression  -C  options  outlined  above,  there  are  a  number  of
       options/actions which degrade performance.  These are, from most expensive to least:

           %option yylineno
           arbitrary trailing context

           pattern sets that require backing up
           %option interactive
           %option always-interactive

           '^' beginning-of-line operator

       with  the  first three all being quite expensive and the last two being quite cheap.  Note
       also that unput() is implemented as a routine call that potentially does quite  a  bit  of
       work,  while yyless() is a quite-cheap macro; so if just putting back some excess text you
       scanned, use yyless().

       REJECT should be avoided at all costs when performance is important.  It is a particularly
       expensive option.

       Getting  rid  of  backing  up  is  messy and often may be an enormous amount of work for a
       complicated scanner.  In principal, one  begins  by  using  the  -b  flag  to  generate  a
       lex.backup file.  For example, on the input

           foo        return TOK_KEYWORD;
           foobar     return TOK_KEYWORD;

       the file looks like:

           State #6 is non-accepting -
            associated rule line numbers:
                  2       3
            out-transitions: [ o ]
            jam-transitions: EOF [ \001-n  p-\177 ]

           State #8 is non-accepting -
            associated rule line numbers:
            out-transitions: [ a ]
            jam-transitions: EOF [ \001-`  b-\177 ]

           State #9 is non-accepting -
            associated rule line numbers:
            out-transitions: [ r ]
            jam-transitions: EOF [ \001-q  s-\177 ]

           Compressed tables always back up.

       The first few lines tell us that there's a scanner state in which it can make a transition
       on an 'o' but not on any other character, and that in that  state  the  currently  scanned
       text  does  not  match any rule.  The state occurs when trying to match the rules found at
       lines 2 and 3 in the input file.  If the scanner is in that state and then reads something
       other than an 'o', it will have to back up to find a rule which is matched.  With a bit of
       headscratching one can see that this must be the state it's in  when  it  has  seen  "fo".
       When  this has happened, if anything other than another 'o' is seen, the scanner will have
       to back up to simply match the 'f' (by the default rule).

       The comment regarding State #8 indicates there's a problem when "foob" has  been  scanned.
       Indeed,  on  any  character  other than an 'a', the scanner will have to back up to accept
       "foo".  Similarly, the comment for State #9 concerns when "fooba" has been scanned and  an
       'r' does not follow.

       The  final  comment  reminds us that there's no point going to all the trouble of removing
       backing up from the rules unless we're using -Cf or -CF, since there's no performance gain
       doing so with compressed scanners.

       The way to remove the backing up is to add "error" rules:

           foo         return TOK_KEYWORD;
           foobar      return TOK_KEYWORD;

           fooba       |
           foob        |
           fo          {
                       /* false alarm, not really a keyword */
                       return TOK_ID;

       Eliminating backing up among a list of keywords can also be done using a "catch-all" rule:

           foo         return TOK_KEYWORD;
           foobar      return TOK_KEYWORD;

           [a-z]+      return TOK_ID;

       This is usually the best solution when appropriate.

       Backing up messages tend to cascade.  With a complicated set of rules it's not uncommon to
       get hundreds of messages.  If one can decipher them, though, it often only takes  a  dozen
       or  so  rules  to eliminate the backing up (though it's easy to make a mistake and have an
       error rule accidentally match a valid token.  A possible future flex feature  will  be  to
       automatically add rules to eliminate backing up).

       It's  important  to keep in mind that you gain the benefits of eliminating backing up only
       if you eliminate every instance of backing up.  Leaving just one means you gain nothing.

       Variable trailing context (where both the leading and trailing parts do not have  a  fixed
       length)  entails  almost the same performance loss as REJECT (i.e., substantial).  So when
       possible a rule like:

           mouse|rat/(cat|dog)   run();

       is better written:

           mouse/cat|dog         run();
           rat/cat|dog           run();

       or as

           mouse|rat/cat         run();
           mouse|rat/dog         run();

       Note that here the special '|' action does not provide any  savings,  and  can  even  make
       things worse (see Deficiencies / Bugs below).

       Another area where the user can increase a scanner's performance (and one that's easier to
       implement) arises from the fact that the longer the tokens matched, the faster the scanner
       will  run.  This is because with long tokens the processing of most input characters takes
       place in the (short) inner scanning loop, and does  not  often  have  to  go  through  the
       additional  work  of  setting  up  the scanning environment (e.g., yytext) for the action.
       Recall the scanner for C comments:

           %x comment
                   int line_num = 1;

           "/*"         BEGIN(comment);

           <comment>\n             ++line_num;
           <comment>"*"+"/"        BEGIN(INITIAL);

       This could be sped up by writing it as:

           %x comment
                   int line_num = 1;

           "/*"         BEGIN(comment);

           <comment>[^*\n]*\n      ++line_num;
           <comment>"*"+[^*/\n]*\n ++line_num;
           <comment>"*"+"/"        BEGIN(INITIAL);

       Now instead of each newline requiring the processing of another  action,  recognizing  the
       newlines  is  "distributed"  over  the  other  rules  to  keep the matched text as long as
       possible.  Note that adding rules does not slow  down  the  scanner!   The  speed  of  the
       scanner  is  independent of the number of rules or (modulo the considerations given at the
       beginning of this section) how complicated the rules are with regard to operators such  as
       '*' and '|'.

       A  final  example  in  speeding  up  a  scanner:  suppose  you want to scan through a file
       containing identifiers and keywords, one per line and with no other extraneous characters,
       and recognize all the keywords.  A natural first approach is:

           asm      |
           auto     |
           break    |
           ... etc ...
           volatile |
           while    /* it's a keyword */

           .|\n     /* it's not a keyword */

       To eliminate the back-tracking, introduce a catch-all rule:

           asm      |
           auto     |
           break    |
           ... etc ...
           volatile |
           while    /* it's a keyword */

           [a-z]+   |
           .|\n     /* it's not a keyword */

       Now,  if  it's  guaranteed  that there's exactly one word per line, then we can reduce the
       total number of matches by a half by merging in the recognition of newlines with  that  of
       the other tokens:

           asm\n    |
           auto\n   |
           break\n  |
           ... etc ...
           volatile\n |
           while\n  /* it's a keyword */

           [a-z]+\n |
           .|\n     /* it's not a keyword */

       One  has  to be careful here, as we have now reintroduced backing up into the scanner.  In
       particular, while we know that there will never be any  characters  in  the  input  stream
       other  than letters or newlines, flex can't figure this out, and it will plan for possibly
       needing to back up when it has scanned a token like "auto" and then the next character  is
       something  other  than  a  newline  or  a letter.  Previously it would then just match the
       "auto" rule and be done, but now it has  no  "auto"  rule,  only  an  "auto\n"  rule.   To
       eliminate  the  possibility of backing up, we could either duplicate all rules but without
       final newlines, or, since we never expect to encounter such an input and  therefore  don't
       how  it's  classified,  we  can  introduce one more catch-all rule, this one which doesn't
       include a newline:

           asm\n    |
           auto\n   |
           break\n  |
           ... etc ...
           volatile\n |
           while\n  /* it's a keyword */

           [a-z]+\n |
           [a-z]+   |
           .|\n     /* it's not a keyword */

       Compiled with -Cf, this is about as fast as one can get a flex  scanner  to  go  for  this
       particular problem.

       A  final  note:  flex  is  slow  when  matching  NUL's, particularly when a token contains
       multiple NUL's.  It's best to write rules which  match  short  amounts  of  text  if  it's
       anticipated that the text will often include NUL's.

       Another  final note regarding performance: as mentioned above in the section How the Input
       is Matched, dynamically resizing yytext to accommodate  huge  tokens  is  a  slow  process
       because it presently requires that the (huge) token be rescanned from the beginning.  Thus
       if performance is vital, you should attempt to match "large" quantities of  text  but  not
       "huge" quantities, where the cutoff between the two is at about 8K characters/token.


       flex  provides two different ways to generate scanners for use with C++.  The first way is
       to simply compile a scanner generated by  flex  using  a  C++  compiler  instead  of  a  C
       compiler.  You should not encounter any compilations errors (please report any you find to
       the email address given in the Author section below).  You can then use C++ code  in  your
       rule  actions  instead  of  C  code.   Note that the default input source for your scanner
       remains yyin, and default echoing is still done to yyout.  Both of  these  remain  FILE  *
       variables and not C++ streams.

       You  can  also  use  flex  to  generate  a  C++  scanner  class,  using the -+ option (or,
       equivalently, %option c++), which is automatically specified  if  the  name  of  the  flex
       executable  ends  in  a  '+',  such  as  flex++.  When using this option, flex defaults to
       generating the scanner to the file instead of lex.yy.c.  The  generated  scanner
       includes the header file FlexLexer.h, which defines the interface to two C++ classes.

       The  first  class, FlexLexer, provides an abstract base class defining the general scanner
       class interface.  It provides the following member functions:

       const char* YYText()
              returns the text of the most recently matched token, the equivalent of yytext.

       int YYLeng()
              returns the length of the most recently matched token, the equivalent of yyleng.

       int lineno() const
              returns the current input line number (see  %option  yylineno),  or  1  if  %option
              yylineno was not used.

       void set_debug( int flag )
              sets  the  debugging flag for the scanner, equivalent to assigning to yy_flex_debug
              (see the Options section above).  Note  that  you  must  build  the  scanner  using
              %option debug to include debugging information in it.

       int debug() const
              returns the current setting of the debugging flag.

       Also provided are member functions equivalent to yy_switch_to_buffer(), yy_create_buffer()
       (though the  first  argument  is  an  std::istream*  object  pointer  and  not  a  FILE*),
       yy_flush_buffer(),  yy_delete_buffer(),  and  yyrestart()  (again, the first argument is a
       std::istream* object pointer).

       The second class defined in FlexLexer.h is yyFlexLexer, which is derived  from  FlexLexer.
       It defines the following additional member functions:

       yyFlexLexer( std::istream* arg_yyin = 0, std::ostream* arg_yyout = 0 )
              constructs  a  yyFlexLexer object using the given streams for input and output.  If
              not specified, the streams default to cin and cout, respectively.

       virtual int yylex()
              performs the same role is yylex() does for ordinary flex  scanners:  it  scans  the
              input  stream,  consuming  tokens,  until  a rule's action returns a value.  If you
              derive a subclass S from yyFlexLexer and want to access the  member  functions  and
              variables  of  S inside yylex(), then you need to use %option yyclass="S" to inform
              flex that you will be using that subclass instead of yyFlexLexer.   In  this  case,
              rather  than  generating  yyFlexLexer::yylex(), flex generates S::yylex() (and also
              generates a dummy  yyFlexLexer::yylex()  that  calls  yyFlexLexer::LexerError()  if

       virtual void switch_streams(std::istream* new_in = 0,
              std::ostream*  new_out  =  0)  reassigns  yyin  to new_in (if non-nil) and yyout to
              new_out (ditto), deleting the previous input buffer if yyin is reassigned.

       int yylex( std::istream* new_in, std::ostream* new_out = 0 )
              first switches the input streams via switch_streams( new_in,  new_out  )  and  then
              returns the value of yylex().

       In  addition,  yyFlexLexer defines the following protected virtual functions which you can
       redefine in derived classes to tailor the scanner:

       virtual int LexerInput( char* buf, int max_size )
              reads up to max_size characters into buf and returns the number of characters read.
              To  indicate  end-of-input,  return 0 characters.  Note that "interactive" scanners
              (see the -B and -I  flags)  define  the  macro  YY_INTERACTIVE.   If  you  redefine
              LexerInput()  and  need  to  take different actions depending on whether or not the
              scanner might be scanning an  interactive  input  source,  you  can  test  for  the
              presence of this name via #ifdef.

       virtual void LexerOutput( const char* buf, int size )
              writes  out  size  characters from the buffer buf, which, while NUL-terminated, may
              also contain "internal" NUL's if the scanner's rules can match text with  NUL's  in

       virtual void LexerError( const char* msg )
              reports  a  fatal  error  message.  The default version of this function writes the
              message to the stream cerr and exits.

       Note that a yyFlexLexer object contains its entire scanning state.  Thus you can use  such
       objects  to create reentrant scanners.  You can instantiate multiple instances of the same
       yyFlexLexer class, and you can also combine multiple C++ scanner classes together  in  the
       same program using the -P option discussed above.

       Finally,  note  that  the %array feature is not available to C++ scanner classes; you must
       use %pointer (the default).

       Here is an example of a simple C++ scanner:

               // An example of using the flex C++ scanner class.

           int mylineno = 0;

           string  \"[^\n"]+\"

           ws      [ \t]+

           alpha   [A-Za-z]
           dig     [0-9]
           name    ({alpha}|{dig}|\$)({alpha}|{dig}|[_.\-/$])*
           num1    [-+]?{dig}+\.?([eE][-+]?{dig}+)?
           num2    [-+]?{dig}*\.{dig}+([eE][-+]?{dig}+)?
           number  {num1}|{num2}


           {ws}    /* skip blanks and tabs */

           "/*"    {
                   int c;

                   while((c = yyinput()) != 0)
                       if(c == '\n')

                       else if(c == '*')
                           if((c = yyinput()) == '/')

           {number}  cout << "number " << YYText() << '\n';

           \n        mylineno++;

           {name}    cout << "name " << YYText() << '\n';

           {string}  cout << "string " << YYText() << '\n';


           int main( int /* argc */, char** /* argv */ )
               FlexLexer* lexer = new yyFlexLexer;
               while(lexer->yylex() != 0)
               return 0;
       If you want to create multiple (different) lexer classes, you use  the  -P  flag  (or  the
       prefix=  option)  to  rename  each  yyFlexLexer  to  some other xxFlexLexer.  You then can
       include <FlexLexer.h>  in  your  other  sources  once  per  lexer  class,  first  renaming
       yyFlexLexer as follows:

           #undef yyFlexLexer
           #define yyFlexLexer xxFlexLexer
           #include <FlexLexer.h>

           #undef yyFlexLexer
           #define yyFlexLexer zzFlexLexer
           #include <FlexLexer.h>

       if,  for  example,  you  used  %option  prefix="xx"  for  one of your scanners and %option
       prefix="zz" for the other.

       IMPORTANT: the present  form  of  the  scanning  class  is  experimental  and  may  change
       considerably between major releases.


       flex  is  a  rewrite  of  the AT&T Unix lex tool (the two implementations do not share any
       code, though), with some extensions and incompatibilities, both of which are of concern to
       those  who  wish  to  write  scanners  acceptable to either implementation.  Flex is fully
       compliant with the POSIX lex specification, except that when using %pointer (the default),
       a  call  to  unput()  destroys  the  contents  of  yytext,  which  is counter to the POSIX

       In this section we discuss all of the known areas of incompatibility  between  flex,  AT&T
       lex, and the POSIX specification.

       flex's -l option turns on maximum compatibility with the original AT&T lex implementation,
       at the cost of a major loss in the generated scanner's performance.  We note  below  which
       incompatibilities can be overcome using the -l option.

       flex is fully compatible with lex with the following exceptions:

       -      The  undocumented lex scanner internal variable yylineno is not supported unless -l
              or %option yylineno is used.

              yylineno should be maintained on a per-buffer  basis,  rather  than  a  per-scanner
              (single global variable) basis.

              yylineno is not part of the POSIX specification.

       -      The  input() routine is not redefinable, though it may be called to read characters
              following whatever has been matched by a rule.  If input()  encounters  an  end-of-
              file the normal yywrap() processing is done.  A ``real'' end-of-file is returned by
              input() as EOF.

              Input is instead controlled by defining the YY_INPUT macro.

              The flex restriction that input() cannot be redefined is  in  accordance  with  the
              POSIX  specification,  which  simply  does  not  specify any way of controlling the
              scanner's input other than by making an initial assignment to yyin.

       -      The unput() routine is not redefinable.  This restriction  is  in  accordance  with

       -      flex  scanners are not as reentrant as lex scanners.  In particular, if you have an
              interactive scanner and an interrupt handler which long-jumps out of  the  scanner,
              and the scanner is subsequently called again, you may get the following message:

                  fatal flex scanner internal error--end of buffer missed

              To reenter the scanner, first use

                  yyrestart( yyin );

              Note  that  this  call  will  throw  away  any buffered input; usually this isn't a
              problem with an interactive scanner.

              Also note that flex C++ scanner classes are reentrant, so if using C++ is an option
              for  you,  you  should  use  them instead.  See "Generating C++ Scanners" above for

       -      output() is not supported.  Output from the ECHO macro is done to the  file-pointer
              yyout (default stdout).

              output() is not part of the POSIX specification.

       -      lex  does not support exclusive start conditions (%x), though they are in the POSIX

       -      When definitions are expanded, flex encloses them in parentheses.   With  lex,  the

                  NAME    [A-Z][A-Z0-9]*
                  foo{NAME}?      printf( "Found it\n" );

              will  not  match  the  string  "foo" because when the macro is expanded the rule is
              equivalent to "foo[A-Z][A-Z0-9]*?"  and the precedence is  such  that  the  '?'  is
              associated with "[A-Z0-9]*".  With flex, the rule will be expanded to "foo([A-Z][A-
              Z0-9]*)?" and so the string "foo" will match.

              Note that if the definition begins with ^ or ends with $ then it  is  not  expanded
              with  parentheses, to allow these operators to appear in definitions without losing
              their special meanings.  But the <s>, /, and <<EOF>> operators cannot be used in  a
              flex definition.

              Using -l results in the lex behavior of no parentheses around the definition.

              The POSIX specification is that the definition be enclosed in parentheses.

       -      Some  implementations  of lex allow a rule's action to begin on a separate line, if
              the rule's pattern has trailing whitespace:

                  foo|bar<space here>
                    { foobar_action(); }

              flex does not support this feature.

       -      The lex %r (generate a Ratfor scanner) option is not supported.  It is not part  of
              the POSIX specification.

       -      After  a  call  to  unput(),  yytext  is undefined until the next token is matched,
              unless the scanner was built using %array.  This is not the case with  lex  or  the
              POSIX specification.  The -l option does away with this incompatibility.

       -      The  precedence  of  the  {} (numeric range) operator is different.  lex interprets
              "abc{1,3}" as "match one,  two,  or  three  occurrences  of  'abc'",  whereas  flex
              interprets  it  as  "match 'ab' followed by one, two, or three occurrences of 'c'".
              The latter is in agreement with the POSIX specification.

       -      The precedence of the ^ operator is different.  lex interprets "^foo|bar" as "match
              either  'foo'  at  the  beginning  of  a  line,  or  'bar'  anywhere", whereas flex
              interprets it as "match either 'foo' or 'bar' if they come at the  beginning  of  a
              line".  The latter is in agreement with the POSIX specification.

       -      The special table-size declarations such as %a supported by lex are not required by
              flex scanners; flex ignores them.

       -      The name FLEX_SCANNER is #define'd so scanners may be written for use  with  either
              flex or lex.  Scanners also include YY_FLEX_MAJOR_VERSION and YY_FLEX_MINOR_VERSION
              indicating which version of flex generated the scanner (for example,  for  the  2.5
              release, these defines would be 2 and 5 respectively).

       The following flex features are not included in lex or the POSIX specification:

           C++ scanners
           start condition scopes
           start condition stacks
           interactive/non-interactive scanners
           yy_scan_string() and friends
           #line directives
           %{}'s around actions
           multiple actions on a line

       plus  almost  all of the flex flags.  The last feature in the list refers to the fact that
       with flex you can put multiple actions on the same line, separated with semi-colons, while
       with lex, the following

           foo    handle_foo(); ++num_foos_seen;

       is (rather surprisingly) truncated to

           foo    handle_foo();

       flex  does  not  truncate  the action.  Actions that are not enclosed in braces are simply
       terminated at the end of the line.


       warning, rule cannot be matched indicates that the given rule cannot be matched because it
       follows  other  rules  that  will  always  match the same text as it.  For example, in the
       following "foo" cannot be matched because it comes after an identifier "catch-all" rule:

           [a-z]+    got_identifier();
           foo       got_foo();

       Using REJECT in a scanner suppresses this warning.

       warning, -s option given but default rule  can  be  matched  means  that  it  is  possible
       (perhaps  only  in  a  particular start condition) that the default rule (match any single
       character) is the only one that will match  a  particular  input.   Since  -s  was  given,
       presumably this is not intended.

       reject_used_but_not_detected  undefined  or yymore_used_but_not_detected undefined - These
       errors can occur at compile time.  They indicate that the scanner uses REJECT or  yymore()
       but  that flex failed to notice the fact, meaning that flex scanned the first two sections
       looking for occurrences of these actions and failed to find any,  but  somehow  you  snuck
       some  in  (via  a  #include  file,  for example).  Use %option reject or %option yymore to
       indicate to flex that you really do use these features.

       flex scanner jammed - a scanner compiled with -s has encountered  an  input  string  which
       wasn't matched by any of its rules.  This error can also occur due to internal problems.

       token  too large, exceeds YYLMAX - your scanner uses %array and one of its rules matched a
       string longer than the YYLMAX constant (8K bytes by default).  You can increase the  value
       by #define'ing YYLMAX in the definitions section of your flex input.

       scanner  requires  -8  flag to use the character 'x' - Your scanner specification includes
       recognizing the 8-bit character 'x' and you did not specify the -8 flag, and your  scanner
       defaulted  to  7-bit  because  you used the -Cf or -CF table compression options.  See the
       discussion of the -7 flag for details.

       flex scanner push-back overflow - you used unput() to push back  so  much  text  that  the
       scanner's buffer could not hold both the pushed-back text and the current token in yytext.
       Ideally the scanner should dynamically resize the buffer in this case, but at  present  it
       does not.

       input  buffer overflow, can't enlarge buffer because scanner uses REJECT - the scanner was
       working on matching an extremely large token and needed to expand the input buffer.   This
       doesn't work with scanners that use REJECT.

       fatal  flex  scanner  internal  error--end  of buffer missed - This can occur in a scanner
       which is reentered after a long-jump has jumped out (or  over)  the  scanner's  activation
       frame.  Before reentering the scanner, use:

           yyrestart( yyin );

       or, as noted above, switch to using the C++ scanner class.

       too  many  start  conditions  in  <> construct! - you listed more start conditions in a <>
       construct than exist (so you must have listed at least one of them twice).


       -ll    library with which scanners must be linked.

              generated scanner (called lexyy.c on some systems).
              generated C++ scanner class, when using -+.

              header file defining the C++ scanner base class, FlexLexer, and its derived  class,

              skeleton  scanner.   This  file  is  only  used  when  building flex, not when flex

              backing-up information for -b flag (called lex.bck on some systems).


       Some trailing context patterns cannot be properly matched and  generate  warning  messages
       ("dangerous  trailing context").  These are patterns where the ending of the first part of
       the rule matches the beginning of the second part,  such  as  "zx*/xy*",  where  the  'x*'
       matches  the  'x'  at  the  beginning of the trailing context.  (Note that the POSIX draft
       states that the text matched by such patterns is undefined.)

       For some trailing context rules, parts which are actually fixed-length are not  recognized
       as  such, leading to the above mentioned performance loss.  In particular, parts using '|'
       or {n} (such as "foo{3}") are always considered variable-length.

       Combining trailing context with the special  '|'  action  can  result  in  fixed  trailing
       context  being  turned into the more expensive variable trailing context.  For example, in
       the following:

           abc      |

       Use of unput() invalidates yytext and yyleng, unless the %array directive or the -l option
       has been used.

       Pattern-matching of NUL's is substantially slower than matching other characters.

       Dynamic  resizing  of  the  input  buffer  is  slow, as it entails rescanning all the text
       matched so far by the current (generally huge) token.

       Due to both buffering of input and read-ahead, you  cannot  intermix  calls  to  <stdio.h>
       routines,  such  as,  for example, getchar(), with flex rules and expect it to work.  Call
       input() instead.

       The total table entries listed by the -v flag excludes the number of table entries  needed
       to  determine what rule has been matched.  The number of entries is equal to the number of
       DFA states if the scanner does not use REJECT, and somewhat greater  than  the  number  of
       states if it does.

       REJECT cannot be used with the -f or -F options.

       The flex internal algorithms need documentation.


       lex(1), yacc(1), sed(1), awk(1).

       John  Levine, Tony Mason, and Doug Brown, Lex & Yacc, O'Reilly and Associates.  Be sure to
       get the 2nd edition.

       M. E. Lesk and E. Schmidt, LEX - Lexical Analyzer Generator

       Alfred Aho, Ravi Sethi and Jeffrey Ullman, Compilers: Principles,  Techniques  and  Tools,
       Addison-Wesley   (1986).    Describes   the   pattern-matching  techniques  used  by  flex
       (deterministic finite automata).


       Vern Paxson, with the help of many ideas and much inspiration from Van Jacobson.  Original
       version  by Jef Poskanzer.  The fast table representation is a partial implementation of a
       design done by Van Jacobson.  The implementation was done by Kevin Gong and Vern Paxson.

       Thanks to the many flex beta-testers, feedbackers, and contributors,  especially  Francois
       Pinard, Casey Leedom, Robert Abramovitz, Stan Adermann, Terry Allen, David Barker-Plummer,
       John Basrai, Neal Becker, Nelson H.F. Beebe,, Karl Berry, Peter  A.  Bigot,
       Simon  Blanchard,  Keith Bostic, Frederic Brehm, Ian Brockbank, Kin Cho, Nick Christopher,
       Brian Clapper, J.T. Conklin, Jason Coughlin, Bill Cox, Nick Cropper,  Dave  Curtis,  Scott
       David  Daniels,  Chris  G.  Demetriou,  Theo  de  Raadt, Mike Donahue, Chuck Doucette, Tom
       Epperly, Leo Eskin, Chris Faylor, Chris Flatters, Jon Forrest, Jeffrey Friedl, Joe  Gayda,
       Kaveh  R.  Ghazi,  Wolfgang Glunz, Eric Goldman, Christopher M. Gould, Ulrich Grepel, Peer
       Griebel, Jan Hajic, Charles Hemphill, NORO Hideo, Jarkko Hietaniemi, Scott  Hofmann,  Jeff
       Honig,  Dana Hudes, Eric Hughes, John Interrante, Ceriel Jacobs, Michal Jaegermann, Sakari
       Jalovaara, Jeffrey R. Jones, Henry Juengst, Klaus Kaempf, Jonathan I. Kamens,  Terrence  O
       Kane,  Amir  Katz,, Kevin B. Kenny, Steve Kirsch, Winfried Koenig, Marq
       Kole, Ronald Lamprecht, Greg Lee, Rohan Lenard, Craig Leres, John  Levine,  Steve  Liddle,
       David  Loffredo,  Mike  Long,  Mohamed  el  Lozy, Brian Madsen, Malte, Joe Marshall, Bengt
       Martensson, Chris Metcalf, Luke Mewburn, Jim Meyering, R. Alexander Milowski, Erik Naggum,
       G.T.  Nicol, Landon Noll, James Nordby, Marc Nozell, Richard Ohnemus, Karsten Pahnke, Sven
       Panne, Roland Pesch, Walter Pelissero, Gaumond Pierre, Esmond  Pitt,  Jef  Poskanzer,  Joe
       Rahmeh,  Jarmo  Raiha, Frederic Raimbault, Pat Rankin, Rick Richardson, Kevin Rodgers, Kai
       Uwe  Rommel,  Jim  Roskind,  Alberto  Santini,  Andreas  Scherer,  Darrell  Schiebel,  Raf
       Schietekat,  Doug  Schmidt,  Philippe  Schnoebelen,  Andreas Schwab, Larry Schwimmer, Alex
       Siegel, Eckehard Stolz, Jan-Erik Strvmquist, Mike Stump, Paul Stuart,  Dave  Tallman,  Ian
       Lance  Taylor,  Chris  Thewalt,  Richard  M. Timoney, Jodi Tsai, Paul Tuinenga, Gary Weik,
       Frank Whaley, Gerhard Wilhelms, Kent Williams, Ken Yap, Ron Zellar,  Nathan  Zelle,  David
       Zuhn,  and  those  whose  names  have  slipped my marginal mail-archiving skills but whose
       contributions are appreciated all the same.

       Thanks to Keith Bostic, Jon Forrest,  Noah  Friedman,  John  Gilmore,  Craig  Leres,  John
       Levine,  Bob  Mulcahy,  G.T.   Nicol, Francois Pinard, Rich Salz, and Richard Stallman for
       help with various distribution headaches.

       Thanks to Esmond Pitt and Earle Horton for 8-bit character support;  to  Benson  Margulies
       and Fred Burke for C++ support; to Kent Williams and Tom Epperly for C++ class support; to
       Ove Ewerlid for support of NUL's; and to Eric Hughes for support of multiple buffers.

       This work was primarily done when I was with the Real Time Systems Group at  the  Lawrence
       Berkeley Laboratory in Berkeley, CA.  Many thanks to all there for the support I received.

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