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           #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).
                  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-
                  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  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.
           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
           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.
           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)

    GNU 2014-01-11 SCANF(3)


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