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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 'm' character.  This is used with string conversions
              (%s, %c, %[), 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.

       ·      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 ('')  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 (''),
              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 'a' assignment-allocation modifier
       Originally, the GNU C library supported dynamic allocation  for  string
       inputs (as a nonstandard extension) via the a character.  (This feature
       is present at least as far back as glibc 2.0.)  Thus, one  could  write
       the  following  to  have scanf() allocate a buffer for an input string,
       with a pointer to that buffer being returned in *buf:

           char *buf;
           scanf("%as", &buf);

       The use of the letter a for this purpose was problematic,  since  a  is
       also specified by the ISO C standard as a synonym for f (floating-point
       input).  POSIX.1-2008 instead specifies the m modifier  for  assignment
       allocation (as documented in DESCRIPTION, above).

       Note  that  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).

       Support for the m modifier was added to  glibc  starting  with  version
       2.7, and new programs should use that modifier instead of a.

       As  well  as  being  standardized  by  POSIX,  the  m  modifier has the
       following further advantages over the use of a:

       * 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.).

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.

EXAMPLE

       To use the dynamic allocation conversion  specifier,  specify  m  as  a
       length  modifier  (thus %ms or %m[range]).  The caller must free(3) the
       returned string, as in the following example:

           char *p;
           int n;

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

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

SEE ALSO

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

COLOPHON

       This  page  is  part of release 3.65 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/.



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