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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():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

       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:

       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  charac-
       ter '%' or the character 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 successful
	      assignments returned by scanf().

       o      For decimal conversions, an optional quote character (').	  This
	      specifies	 that  the input number may include thousands' separa-
	      tors as defined  by  the	LC_NUMERIC  category  of  the  current
	      locale.  (See setlocale(3).)  The quote character may precede or
	      follow the '*' assignment-suppression character.

       o      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.

       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 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.

       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  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 the initial element of a 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 and
	      does not increase the  count  returned  by  the  function.   The
	      assignment  can  be suppressed with the * assignment-suppression
	      character, but the effect on  the	 return	 value	is  undefined.
	      Therefore %*n conversions should not be used.

       On  success,  these functions return the number of input items success-
       fully matched and assigned; this 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 to 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.

       For  an	explanation  of	 the  terms  used   in	 this	section,   see

       |Interface	     | Attribute     | Value	      |
       |scanf(), fscanf(),   | Thread safety | MT-Safe locale |
       |sscanf(), vscanf(),  |		     |		      |
       |vsscanf(), vfscanf() |		     |		      |

       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)

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GNU				  2017-03-13			      SCANF(3)