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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 toward the maximum field  width.   String
              input  conversions  store a terminating null byte ('\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  backward  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 byte ('\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 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.