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NAME

       scanf,   fscanf,  sscanf,  vscanf,  vsscanf,  vfscanf  -  input  format
       conversion

SYNOPSIS

       #include <stdio.h>

       int scanf(const char *format, ...);
       int fscanf(FILE *stream, const char *format, ...);
       int sscanf(const char *str, const char *format, ...);

       #include <stdarg.h>

       int vscanf(const char *format, va_list ap);
       int vsscanf(const char *str, const char *format, va_list ap);
       int vfscanf(FILE *stream, const char *format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       vscanf(), vsscanf(), vfscanf():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

DESCRIPTION

       The  scanf()  family  of  functions  scans input according to format as
       described below.  This format may  contain  conversion  specifications;
       the  results from such conversions, if any, are stored in the locations
       pointed to by the pointer arguments that follow format.   Each  pointer
       argument  must  be of a type that is appropriate for the value returned
       by the corresponding conversion specification.

       If the number of conversion specifications in format exceeds the number
       of  pointer  arguments,  the  results  are undefined.  If the number of
       pointer arguments exceeds the number of conversion specifications, then
       the excess pointer arguments are evaluated, but are otherwise ignored.

       The  scanf() function reads input from the standard input stream stdin,
       fscanf() reads input from the stream pointer stream, and sscanf() reads
       its input from the character string pointed to by str.

       The vfscanf() function is analogous to vfprintf(3) and reads input from
       the stream pointer stream using a variable argument  list  of  pointers
       (see  stdarg(3).   The vscanf() function scans a variable argument list
       from the standard input and the vsscanf()  function  scans  it  from  a
       string; these are analogous to the vprintf(3) and vsprintf(3) functions
       respectively.

       The format string consists of a sequence of directives  which  describe
       how  to  process  the sequence of input characters.  If processing of a
       directive fails, no further input is  read,  and  scanf()  returns.   A
       "failure"  can  be either of the following: input failure, meaning that
       input characters were unavailable, or matching  failure,  meaning  that
       the input was inappropriate (see below).

       A directive is one of the following:

       o      A sequence of white-space characters (space, tab, newline, etc.;
              see isspace(3)).  This directive matches  any  amount  of  white
              space, including none, in the input.

       o      An ordinary character (i.e., one other than white space or '%').
              This character must exactly match the next character of input.

       o      A conversion specification, which commences with a '%' (percent)
              character.  A sequence of characters from the input is converted
              according to this specification, and the result is placed in the
              corresponding  pointer argument.  If the next item of input does
              not match the conversion specification, the conversion fails  --
              this is a matching failure.

       Each   conversion  specification  in  format  begins  with  either  the
       character '%' or the  character  sequence  "%n$"  (see  below  for  the
       distinction) followed by:

       o      An  optional '*' assignment-suppression character: scanf() reads
              input as directed by the conversion specification, but  discards
              the  input.   No corresponding pointer argument is required, and
              this specification is not included in the  count  of  successful
              assignments returned by scanf().

       o      An   optional   'a'   character.    This  is  used  with  string
              conversions, and relieves the caller of the need to  allocate  a
              corresponding   buffer  to  hold  the  input:  instead,  scanf()
              allocates a buffer of sufficient size, and assigns  the  address
              of  this  buffer  to  the  corresponding pointer argument, which
              should be a pointer to a char * variable (this variable does not
              need  to  be  initialized  before  the call).  The caller should
              subsequently free(3) this buffer when it is no longer  required.
              This  is  a  GNU  extension;  C99 employs the 'a' character as a
              conversion specifier (and it can also be used as such in the GNU
              implementation).

       o      An  optional  decimal  integer which specifies the maximum field
              width.  Reading of characters stops either when this maximum  is
              reached  or  when  a  nonmatching  character is found, whichever
              happens first.  Most conversions  discard  initial  white  space
              characters (the exceptions are noted below), and these discarded
              characters don't count towards the maximum field width.   String
              input conversions store a null terminator ('\0') to mark the end
              of the input; the maximum field  width  does  not  include  this
              terminator.

       o      An  optional  type  modifier character.  For example, the l type
              modifier is used with integer conversions such as %d to  specify
              that  the  corresponding  pointer  argument refers to a long int
              rather than a pointer to an int.

       o      A  conversion  specifier  that  specifies  the  type  of   input
              conversion to be performed.

       The  conversion  specifications  in  format  are  of  two forms, either
       beginning with '%' or beginning with "%n$".  The two forms  should  not
       be  mixed  in  the  same format string, except that a string containing
       "%n$" specifications can include %% and %*.   If  format  contains  '%'
       specifications  then  these correspond in order with successive pointer
       arguments.  In the "%n$" form (which is specified in POSIX.1-2001,  but
       not  C99),  n  is  a  decimal integer that specifies that the converted
       input should be placed in the location referred to by the n-th  pointer
       argument following format.

   Conversions
       The  following  type  modifier  characters  can  appear in a conversion
       specification:

       h      Indicates that the conversion will be one of d, i, o, u,  x,  X,
              or  n  and  the  next  pointer  is  a  pointer to a short int or
              unsigned short int (rather than int).

       hh     As for h, but the next pointer is a pointer to a signed char  or
              unsigned char.

       j      As  for h, but the next pointer is a pointer to an intmax_t or a
              uintmax_t.  This modifier was introduced in C99.

       l      Indicates either that the conversion will be one of d, i, o,  u,
              x,  X,  or  n and the next pointer is a pointer to a long int or
              unsigned long int (rather than int), or that the conversion will
              be one of e, f, or g and the next pointer is a pointer to double
              (rather than float).  Specifying two l characters is  equivalent
              to  L.   If  used  with  %c or %s the corresponding parameter is
              considered as a pointer to a wide  character  or  wide-character
              string respectively.

       L      Indicates  that the conversion will be either e, f, or g and the
              next pointer is a pointer to long double or the conversion  will
              be  d,  i,  o, u, or x and the next pointer is a pointer to long
              long.

       q      equivalent to L.  This specifier does not exist in ANSI C.

       t      As for h, but the next pointer is  a  pointer  to  a  ptrdiff_t.
              This modifier was introduced in C99.

       z      As  for  h, but the next pointer is a pointer to a size_t.  This
              modifier was introduced in C99.

       The following conversion specifiers are available:

       %      Matches a literal '%'.  That is, %% in the format string matches
              a  single  input  '%'  character.   No  conversion  is done (but
              initial white space characters are  discarded),  and  assignment
              does not occur.

       d      Matches  an  optionally signed decimal integer; the next pointer
              must be a pointer to int.

       D      Equivalent to ld; this exists only for backwards  compatibility.
              (Note:  thus  only  in  libc4.   In  libc5  and  glibc the %D is
              silently ignored, causing old programs to fail mysteriously.)

       i      Matches an optionally signed integer; the next pointer must be a
              pointer  to  int.   The  integer is read in base 16 if it begins
              with 0x or 0X, in base 8 if it begins with 0,  and  in  base  10
              otherwise.   Only  characters  that  correspond  to the base are
              used.

       o      Matches an unsigned octal integer; the next pointer  must  be  a
              pointer to unsigned int.

       u      Matches  an unsigned decimal integer; the next pointer must be a
              pointer to unsigned int.

       x      Matches an unsigned hexadecimal integer; the next  pointer  must
              be a pointer to unsigned int.

       X      Equivalent to x.

       f      Matches  an  optionally  signed  floating-point number; the next
              pointer must be a pointer to float.

       e      Equivalent to f.

       g      Equivalent to f.

       E      Equivalent to f.

       a      (C99) Equivalent to f.

       s      Matches a  sequence  of  non-white-space  characters;  the  next
              pointer must be a pointer to character array that is long enough
              to hold the input sequence and the  terminating  null  character
              ('\0'), which is added automatically.  The input string stops at
              white space or at the  maximum  field  width,  whichever  occurs
              first.

       c      Matches  a  sequence  of characters whose length is specified by
              the maximum field width (default 1); the next pointer must be  a
              pointer  to  char,  and  there  must  be enough room for all the
              characters (no terminating null byte is added).  The usual  skip
              of  leading  white  space  is  suppressed.   To skip white space
              first, use an explicit space in the format.

       [      Matches a nonempty sequence of characters from the specified set
              of  accepted  characters;  the next pointer must be a pointer to
              char, and there must be enough room for all  the  characters  in
              the  string,  plus  a  terminating null byte.  The usual skip of
              leading white space is suppressed.  The string is to be made  up
              of  characters  in  (or  not  in)  a  particular set; the set is
              defined by the characters between the open bracket  [  character
              and  a  close  bracket  ]  character.   The  set  excludes those
              characters if the first character after the open  bracket  is  a
              circumflex  (^).  To include a close bracket in the set, make it
              the first character after the open bracket  or  the  circumflex;
              any  other position will end the set.  The hyphen character - is
              also special; when placed between two other characters, it  adds
              all  intervening  characters  to  the set.  To include a hyphen,
              make it the last character before the final close bracket.   For
              instance,  [^]0-9-]  means  the  set  "everything  except  close
              bracket, zero through nine, and hyphen".  The string  ends  with
              the appearance of a character not in the (or, with a circumflex,
              in) set or when the field width runs out.

       p      Matches a pointer value (as printed by %p in printf(3); the next
              pointer must be a pointer to a pointer to void.

       n      Nothing  is expected; instead, the number of characters consumed
              thus far from the input is  stored  through  the  next  pointer,
              which  must  be  a  pointer  to  int.  This is not a conversion,
              although it can be suppressed with the *  assignment-suppression
              character.   The  C  standard says: "Execution of a %n directive
              does  not  increment  the  assignment  count  returned  at   the
              completion of execution" but the Corrigendum seems to contradict
              this.  Probably it is wise not to make any  assumptions  on  the
              effect of %n conversions on the return value.

RETURN VALUE

       These  functions  return the number of input items successfully matched
       and assigned, which can be fewer than provided for, or even zero in the
       event of an early matching failure.

       The  value EOF is returned if the end of input is reached before either
       the first successful conversion or a matching failure occurs.   EOF  is
       also returned if a read error occurs, in which case the error indicator
       for the stream (see ferror(3)) is set, and errno is  set  indicate  the
       error.

ERRORS

       EAGAIN The file descriptor underlying stream is marked nonblocking, and
              the read operation would block.

       EBADF  The file descriptor underlying stream is invalid,  or  not  open
              for reading.

       EILSEQ Input byte sequence does not form a valid character.

       EINTR  The read operation was interrupted by a signal; see signal(7).

       EINVAL Not enough arguments; or format is NULL.

       ENOMEM Out of memory.

       ERANGE The  result  of an integer conversion would exceed the size that
              can be stored in the corresponding integer type.

CONFORMING TO

       The functions fscanf(), scanf(), and sscanf() conform to  C89  and  C99
       and POSIX.1-2001.  These standards do not specify the ERANGE error.

       The  q  specifier is the 4.4BSD notation for long long, while ll or the
       usage of L in integer conversions is the GNU notation.

       The Linux version of these functions is based on the GNU libio library.
       Take  a  look  at the info documentation of GNU libc (glibc-1.08) for a
       more concise description.

NOTES

       The GNU C library supports a  nonstandard  extension  that  causes  the
       library  to  dynamically allocate a string of sufficient size for input
       strings for the %s and %a[range] conversion specifiers.  To make use of
       this  feature,  specify a as a length modifier (thus %as or %a[range]).
       The caller must free(3)  the  returned  string,  as  in  the  following
       example:

           char *p;
           int n;

           errno = 0;
           n = scanf("%a[a-z]", &p);
           if (n == 1) {
               printf("read: %s\n", p);
               free(p);
           } else if (errno != 0) {
               perror("scanf");
           } else {
               fprintf(stderr, "No matching characters\n"):
           }

       As  shown in the above example, it is only necessary to call free(3) if
       the scanf() call successfully read a string.

       The a modifier is not available if the program  is  compiled  with  gcc
       -std=c99   or   gcc   -D_ISOC99_SOURCE   (unless  _GNU_SOURCE  is  also
       specified), in which case the a  is  interpreted  as  a  specifier  for
       floating-point numbers (see above).

       Since  version  2.7,  glibc  also  provides the m modifier for the same
       purpose  as  the  a  modifier.   The  m  modifier  has  the   following
       advantages:

       * It may also be applied to %c conversion specifiers (e.g., %3mc).

       * It  avoids ambiguity with respect to the %a floating-point conversion
         specifier (and is unaffected by gcc -std=c99 etc.)

       * It is specified in the upcoming revision of the POSIX.1 standard.

BUGS

       All functions are fully C89  conformant,  but  provide  the  additional
       specifiers  q  and  a  as well as an additional behavior of the L and l
       specifiers.  The latter may be considered to be a bug,  as  it  changes
       the behavior of specifiers defined in C89.

       Some  combinations  of  the  type  modifiers  and conversion specifiers
       defined by ANSI C do not make sense (e.g.  %Ld).  While they may have a
       well-defined  behavior  on  Linux,  this  need  not  to  be so on other
       architectures.  Therefore it usually is better to  use  modifiers  that
       are  not  defined  by  ANSI  C  at  all, that is, use q instead of L in
       combination with d, i, o, u, x, and X conversions or ll.

       The usage of q is not the same as on 4.4BSD, as it may be used in float
       conversions equivalently to L.

SEE ALSO

       getc(3), printf(3), setlocale(3), strtod(3), strtol(3), strtoul(3)

COLOPHON

       This  page  is  part of release 3.27 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.