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SCANF(3)		   Linux Programmers Manual		     SCANF(3)

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


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


       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

       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

       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  charac
       ter '%' 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  conver
	      sions,  and relieves the caller of the need to allocate a corre
	      sponding 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 implemen

	     An optional decimal integer which specifies  the  maximum	field
	      width.   Reading of characters stops either when this maximum is
	      reached or when a non-matching  character  is  found,  whichever
	      happens  first.	Most  conversions  discard initial white space
	      characters (the exceptions are noted below), and these discarded
	      characters  dont 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 ter

	     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 conver
	      sion to be performed.

       The conversion specifications in format are of two forms, either begin
       ning  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 '%' specifi
       cations then these correspond in order with  successive	pointer  argu
       ments.	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 argu
       ment following format.

       The following type modifier characters can appear in a conversion spec

       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 con
	      sidered  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

       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  ini
	      tial  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

       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

       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 char
	      acters  (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  non-empty  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 charac
	      ters  if the first character after the open bracket is a circum
	      flex (^).  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 comple
	      tion 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.

       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

       EAGAIN The file descriptor underlying stream  is  marked  non-blocking,
       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.

       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.

       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	archi
       tectures.  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.

       The GNU C library supports a non-standard  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  exam

	   char *p;
	   int n;

	   errno = 0;
	   n = scanf("%a[a-z]", &p);
	   if (n == 1) {
	       printf("read: %s\n", p);
	   } else if (errno != 0) {
	   } 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 speci
       fied), 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 pur
       pose 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.

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

       This  page  is  part of release 3.05 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/.

GNU				  2008-07-12			      SCANF(3)

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