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FSCANF(3P)                 POSIX Programmer's Manual                FSCANF(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       fscanf, scanf, sscanf - convert formatted input
SYNOPSIS
       #include <stdio.h>
       int fscanf(FILE *restrict stream, const char *restrict format, ... );
       int scanf(const char *restrict format, ... );
       int sscanf(const char *restrict s, const char *restrict format, ... );

DESCRIPTION
       The fscanf() function shall read from  the  named  input  stream.   The
       scanf()  function  shall read from the standard input stream stdin. The
       sscanf() function shall read from the string  s.  Each  function  reads
       bytes, interprets them according to a format, and stores the results in
       its arguments. Each expects, as  arguments,  a  control  string  format
       described  below,  and  a set of pointer arguments indicating where the
       converted input should be stored. The result is undefined if there  are
       insufficient  arguments  for  the  format.   If the format is exhausted
       while arguments remain, the excess arguments  shall  be  evaluated  but
       otherwise ignored.
       Conversions  can be applied to the nth argument after the format in the
       argument list, rather than to the next unused argument. In  this  case,
       the  conversion  specifier  character  % (see below) is replaced by the
       sequence  "%n$",  where  n  is  a  decimal   integer   in   the   range
       [1,{NL_ARGMAX}].  This  feature  provides  for the definition of format
       strings that select arguments in an order appropriate to specific  lan-
       guages. In format strings containing the "%n$" form of conversion spec-
       ifications, it is unspecified whether numbered arguments in  the  argu-
       ment list can be referenced from the format string more than once.
       The  format  can contain either form of a conversion specification-that
       is, % or "%n$"-but the two forms cannot be mixed within a single format
       string.  The  only exception to this is that %% or %* can be mixed with
       the "%n$" form. When numbered argument specifications are used,  speci-
       fying  the  Nth  argument requires that all the leading arguments, from
       the first to the ( N-1)th, are pointers.
       The fscanf() function in all its forms shall allow detection of a  lan-
       guage-dependent  radix character in the input string. The radix charac-
       ter is defined in the program's locale (category LC_NUMERIC ).  In  the
       POSIX  locale, or in a locale where the radix character is not defined,
       the radix character shall default to a period ( '.' ).
       The format is a character string, beginning and ending in  its  initial
       shift  state, if any, composed of zero or more directives.  Each direc-
       tive is composed of one of the following: one or more white-space char-
       acters  (  <space>s,  <tab>s,  <newline>s,  <vertical-tab>s,  or <form-
       feed>s); an ordinary character (neither '%' nor a  white-space  charac-
       ter);  or  a conversion specification. Each conversion specification is
       introduced by the character '%'  or the character sequence "%n$", after
       which the following appear in sequence:
        * An optional assignment-suppressing character '*' .
        * An  optional  non-zero  decimal  integer  that specifies the maximum
          field width.
        * An option length modifier that specifies the size of  the  receiving
          object.
        * A  conversion specifier character that specifies the type of conver-
          sion to be applied. The valid conversion  specifiers  are  described
          below.
       The  fscanf()  functions  shall execute each directive of the format in
       turn. If a directive fails,  as  detailed  below,  the  function  shall
       return.  Failures  are described as input failures (due to the unavail-
       ability of input bytes) or  matching  failures  (due  to  inappropriate
       input).
       A  directive  composed  of  one or more white-space characters shall be
       executed by reading input until no more valid input can be read, or  up
       to  the  first byte which is not a white-space character, which remains
       unread.
       A directive that is an ordinary character shall be executed as follows:
       the  next  byte shall be read from the input and compared with the byte
       that comprises the directive; if the comparison shows that they are not
       equivalent,  the directive shall fail, and the differing and subsequent
       bytes shall remain  unread.  Similarly,  if  end-of-file,  an  encoding
       error, or a read error prevents a character from being read, the direc-
       tive shall fail.
       A directive that is a conversion specification defines a set of  match-
       ing  input sequences, as described below for each conversion character.
       A conversion specification shall be executed in the following steps.
       Input white-space characters  (as  specified  by  isspace())  shall  be
       skipped,  unless  the conversion specification includes a [, c, C, or n
       conversion specifier.
       An item shall be read from the input, unless the conversion  specifica-
       tion includes an n conversion specifier. An input item shall be defined
       as the longest sequence of input bytes (up  to  any  specified  maximum
       field  width, which may be measured in characters or bytes dependent on
       the conversion specifier) which is an initial subsequence of a matching
       sequence.  The  first  byte,  if any, after the input item shall remain
       unread. If the length of the input item is 0, the execution of the con-
       version specification shall fail; this condition is a matching failure,
       unless end-of-file, an encoding error, or a read error prevented  input
       from the stream, in which case it is an input failure.
       Except  in the case of a % conversion specifier, the input item (or, in
       the case of a %n conversion specification, the count  of  input  bytes)
       shall  be  converted to a type appropriate to the conversion character.
       If the input item is not a matching sequence, the execution of the con-
       version  specification  fails;  this  condition  is a matching failure.
       Unless assignment suppression was indicated by a '*', the result of the
       conversion  shall be placed in the object pointed to by the first argu-
       ment following the format argument that has not already received a con-
       version  result if the conversion specification is introduced by %,  or
       in the nth argument if introduced by the character sequence "%n$".   If
       this  object does not have an appropriate type, or if the result of the
       conversion cannot be represented in the space provided, the behavior is
       undefined.
       The length modifiers and their meanings are:
       hh     Specifies  that  a  following  d, i, o, u, x, X, or n conversion
              specifier applies to an argument with  type  pointer  to  signed
              char or unsigned char.
       h      Specifies  that  a  following  d, i, o, u, x, X, or n conversion
              specifier applies to an argument with type pointer to  short  or
              unsigned short.
       l (ell)
              Specifies  that  a  following  d, i, o, u, x, X, or n conversion
              specifier applies to an argument with type pointer  to  long  or
              unsigned  long;  that a following a, A, e, E, f, F, g, or G con-
              version specifier applies to an argument with  type  pointer  to
              double;  or  that  a  following  c, s, or [ conversion specifier
              applies to an argument with type pointer to wchar_t.
       ll (ell-ell)
              Specifies that a following d, i, o, u, x,  X,  or  n  conversion
              specifier  applies to an argument with type pointer to long long
              or unsigned long long.
       j      Specifies that a following d, i, o, u, x,  X,  or  n  conversion
              specifier  applies  to an argument with type pointer to intmax_t
              or uintmax_t.
       z      Specifies that a following d, i, o, u, x,  X,  or  n  conversion
              specifier  applies to an argument with type pointer to size_t or
              the corresponding signed integer type.
       t      Specifies that a following d, i, o, u, x,  X,  or  n  conversion
              specifier  applies to an argument with type pointer to ptrdiff_t
              or the corresponding unsigned type.
       L      Specifies that a following a, A, e, E, f, F, g, or G  conversion
              specifier  applies to an argument with type pointer to long dou-
              ble.

       If a length modifier appears with any conversion specifier  other  than
       as specified above, the behavior is undefined.
       The following conversion specifiers are valid:
       d      Matches  an  optionally  signed decimal integer, whose format is
              the same as expected for the subject sequence of  strtol()  with
              the  value  10  for  the base argument. In the absence of a size
              modifier, the application shall ensure  that  the  corresponding
              argument is a pointer to int.
       i      Matches  an  optionally signed integer, whose format is the same
              as expected for the subject sequence of strtol() with 0 for  the
              base  argument.  In the absence of a size modifier, the applica-
              tion shall ensure that the corresponding argument is  a  pointer
              to int.
       o      Matches  an optionally signed octal integer, whose format is the
              same as expected for the subject sequence of strtoul() with  the
              value  8  for  the base argument. In the absence of a size modi-
              fier, the application shall ensure that the corresponding  argu-
              ment is a pointer to unsigned.
       u      Matches  an  optionally  signed decimal integer, whose format is
              the same as expected for the subject sequence of strtoul()  with
              the  value  10  for  the base argument. In the absence of a size
              modifier, the application shall ensure  that  the  corresponding
              argument is a pointer to unsigned.
       x      Matches  an  optionally signed hexadecimal integer, whose format
              is the same as expected for the subject  sequence  of  strtoul()
              with  the  value  16  for the base argument. In the absence of a
              size modifier, the application shall ensure that the correspond-
              ing argument is a pointer to unsigned.
       a, e, f, g
              Matches an optionally signed floating-point number, infinity, or
              NaN, whose format is  the  same  as  expected  for  the  subject
              sequence  of  strtod().  In  the absence of a size modifier, the
              application shall ensure that the corresponding  argument  is  a
              pointer to float.
       If  the fprintf() family of functions generates character string repre-
       sentations for infinity and NaN (a symbolic entity encoded in floating-
       point  format)  to  support  IEEE Std 754-1985,  the fscanf() family of
       functions shall recognize them as input.
       s      Matches a sequence of bytes that are not white-space characters.
              The  application shall ensure that the corresponding argument is
              a pointer to the initial byte of an array of char, signed  char,
              or  unsigned char large enough to accept the sequence and a ter-
              minating null character code, which  shall  be  added  automati-
              cally.
       If  an l (ell) qualifier is present, the input is a sequence of charac-
       ters that begins in the initial shift state. Each  character  shall  be
       converted  to  a  wide character as if by a call to the mbrtowc() func-
       tion, with the conversion state described by an mbstate_t  object  ini-
       tialized  to zero before the first character is converted. The applica-
       tion shall ensure that the corresponding argument is a  pointer  to  an
       array  of wchar_t large enough to accept the sequence and the terminat-
       ing null wide character, which shall be added automatically.
       [      Matches a non-empty sequence of bytes from  a  set  of  expected
              bytes (the scanset). The normal skip over white-space characters
              shall be suppressed in this case. The application  shall  ensure
              that the corresponding argument is a pointer to the initial byte
              of an array of char, signed char, or unsigned char large  enough
              to  accept the sequence and a terminating null byte, which shall
              be added automatically.
       If an l (ell) qualifier is present, the input is a sequence of  charac-
       ters  that  begins  in  the  initial shift state. Each character in the
       sequence shall be converted to a wide character as if by a call to  the
       mbrtowc() function, with the conversion state described by an mbstate_t
       object initialized to zero before the first character is converted. The
       application  shall  ensure that the corresponding argument is a pointer
       to an array of wchar_t large enough to accept the sequence and the ter-
       minating null wide character, which shall be added automatically.
       The  conversion specification includes all subsequent bytes in the for-
       mat string up to and including the matching right square bracket (  ']'
       ).  The  bytes  between the square brackets (the scanlist) comprise the
       scanset, unless the byte after the left square bracket is a  circumflex
       (  '^'  ),  in  which  case  the scanset contains all bytes that do not
       appear in the scanlist between the  circumflex  and  the  right  square
       bracket.   If  the  conversion specification begins with "[]" or "[^]",
       the right square bracket is included in the scanlist and the next right
       square  bracket is the matching right square bracket that ends the con-
       version specification; otherwise, the first right square bracket is the
       one that ends the conversion specification. If a '-' is in the scanlist
       and is not the first character, nor the second where the first  charac-
       ter  is  a '^', nor the last character, the behavior is implementation-
       defined.
       c      Matches a sequence of bytes of the number specified by the field
              width (1 if no field width is present in the conversion specifi-
              cation). The application shall  ensure  that  the  corresponding
              argument  is  a pointer to the initial byte of an array of char,
              signed char,  or  unsigned  char  large  enough  to  accept  the
              sequence.  No  null  byte  is added. The normal skip over white-
              space characters shall be suppressed in this case.
       If an l (ell) qualifier is present, the input shall be  a  sequence  of
       characters  that  begins in the initial shift state.  Each character in
       the sequence is converted to a wide character as if by a  call  to  the
       mbrtowc() function, with the conversion state described by an mbstate_t
       object initialized to zero before the first character is converted. The
       application  shall  ensure that the corresponding argument is a pointer
       to an array of wchar_t large enough to accept the resulting sequence of
       wide characters. No null wide character is added.
       p      Matches  an implementation-defined set of sequences, which shall
              be the same as the set of sequences that is produced by  the  %p
              conversion  specification  of  the corresponding fprintf() func-
              tions. The application shall ensure that the corresponding argu-
              ment  is  a  pointer to a pointer to void. The interpretation of
              the input item is implementation-defined. If the input item is a
              value  converted  earlier during the same program execution, the
              pointer that results shall compare equal to that  value;  other-
              wise,  the  behavior of the %p conversion specification is unde-
              fined.
       n      No input is consumed. The application shall ensure that the cor-
              responding argument is a pointer to the integer into which shall
              be written the number of bytes read from the  input  so  far  by
              this  call  to the fscanf() functions. Execution of a %n conver-
              sion specification shall  not  increment  the  assignment  count
              returned  at  the  completion  of  execution of the function. No
              argument shall be converted, but one shall be consumed.  If  the
              conversion   specification  includes  an  assignment-suppressing
              character or a field width, the behavior is undefined.
       C      Equivalent to lc .
       S      Equivalent to ls .
       %      Matches a single '%'  character;  no  conversion  or  assignment
              occurs. The complete conversion specification shall be %% .

       If a conversion specification is invalid, the behavior is undefined.
       The conversion specifiers A, E, F, G, and X are also valid and shall be
       equivalent to a, e, f, g, and x, respectively.
       If end-of-file is encountered during input, conversion shall be  termi-
       nated.   If  end-of-file  occurs  before any bytes matching the current
       conversion specification (except for %n ) have been  read  (other  than
       leading white-space characters, where permitted), execution of the cur-
       rent conversion specification shall terminate with  an  input  failure.
       Otherwise,  unless execution of the current conversion specification is
       terminated with a matching failure, execution of the following  conver-
       sion specification (if any) shall be terminated with an input failure.
       Reaching  the  end  of  the  string  in sscanf() shall be equivalent to
       encountering end-of-file for fscanf().
       If conversion terminates on a conflicting input, the offending input is
       left  unread  in  the  input. Any trailing white space (including <new-
       line>s) shall be left unread unless matched by a conversion  specifica-
       tion. The success of literal matches and suppressed assignments is only
       directly determinable via the %n conversion specification.
       The fscanf() and scanf() functions may mark the st_atime field  of  the
       file  associated  with  stream  for update. The st_atime field shall be
       marked for  update  by  the  first  successful  execution  of  fgetc(),
       fgets(),  fread(),  getc(),  getchar(),  gets(),  fscanf(), or fscanf()
       using stream that  returns  data  not  supplied  by  a  prior  call  to
       ungetc().
RETURN VALUE
       Upon  successful completion, these functions shall return the number of
       successfully matched and assigned input items; this number can be  zero
       in the event of an early matching failure. If the input ends before the
       first matching failure or conversion, EOF shall be returned. If a  read
       error  occurs,  the error indicator for the stream is set, EOF shall be
       returned,  and errno shall be set to indicate the error.
ERRORS
       For the conditions under which the  fscanf()  functions  fail  and  may
       fail, refer to fgetc() or fgetwc().
       In addition, fscanf() may fail if:
       EILSEQ Input byte sequence does not form a valid character.
       EINVAL There are insufficient arguments.

       The following sections are informative.
EXAMPLES
       The call:

              int i, n; float x; char name[50];
              n = scanf("%d%f%s", &i, &x, name);
       with the input line:

              25 54.32E-1 Hamster
       assigns  to n the value 3, to i the value 25, to x the value 5.432, and
       name contains the string "Hamster" .
       The call:

              int i; float x; char name[50];
              (void) scanf("%2d%f%*d %[0123456789]", &i, &x, name);
       with input:

              56789 0123 56a72
       assigns 56 to i, 789.0 to x, skips 0123, and places the  string  "56\0"
       in name. The next call to getchar() shall return the character 'a' .
   Reading Data into an Array
       The  following  call uses fscanf() to read three floating-point numbers
       from standard input into the input array.

              float input[3]; fscanf (stdin, "%f %f %f", input, input+1, input+2);
APPLICATION USAGE
       If the application calling fscanf() has any objects of type  wint_t  or
       wchar_t,  it  must  also  include  the  <wchar.h>  header to have these
       objects defined.
RATIONALE
       This function is aligned with the ISO/IEC 9899:1999  standard,  and  in
       doing  so  a few "obvious" things were not included.  Specifically, the
       set of characters allowed in a scanset is limited to single-byte  char-
       acters.  In  other similar places, multi-byte characters have been per-
       mitted, but for alignment with the ISO/IEC 9899:1999 standard,  it  has
       not been done here. Applications needing this could use the correspond-
       ing wide-character functions to achieve the desired results.
FUTURE DIRECTIONS
       None.
SEE ALSO
       getc(), printf(),  setlocale(),  strtod(),  strtol(),  strtoul(),  wcr-
       tomb(), the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 7,
       Locale, <langinfo.h>, <stdio.h>, <wchar.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the  referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                           FSCANF(3P)