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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:

       ·      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.

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

       ·      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:

       ·      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().

       ·      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).

       ·      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.

       ·      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.

       ·      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/.