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SCANF(3)			    Linux Programmer's Manual				 SCANF(3)

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; 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  cor-
       responding conversion specification.

       If  the	number of conversion specifications in format exceeds the number of pointer argu-
       ments, 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 respec-
       tively.

       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  char-
       acter 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 suc-
	      cessful 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 buf-
	      fer  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  charac-
	      ter  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 intro-
	      duced 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 dis-
	      carded), 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 char-
	      acters; 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  char-
	      acters  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 charac-
	      ter - is also special; when placed between two other characters, it adds all inter-
	      vening  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 success-
       ful 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 inte-
       ger 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  inter-
       preted 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 modi-
       fier.  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 equiv-
       alently to L.

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A  description  of  the
       project,   and	information  about  reporting  bugs,  can  be  found  at  http://www.ker-
       nel.org/doc/man-pages/.

GNU					    2008-07-12					 SCANF(3)
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