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

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

       #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

       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 '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() allo‐
	      cates 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 subse‐
	      quently 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 hap‐
	      pens  first.  Most conversions discard initial white space char‐
	      acters (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 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
	      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

       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 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

       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 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 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 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 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.

       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.

   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 follow‐
       ing 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.).

       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.

       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\n", p);
	   } else if (errno != 0) {
	   } else {
	       fprintf(stderr, "No matching characters\n");

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

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

       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

GNU				  2014-01-11			      SCANF(3)

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