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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 dif-
       fer (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 stan-
       dard input stream stdin. The sscanf() function shall read from the string s. Each function reads bytes,  inter-
       prets  them  according to a format, and stores the results in its arguments. Each expects, as arguments, a con-
       trol 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$", where n is a decimal integer in the range [1,{NL_ARGMAX}]. This feature provides for the  definition  of
       format  strings that select arguments in an order appropriate to specific languages. In format strings contain-
       ing the "%n$" form of conversion specifications, it is unspecified whether numbered arguments in  the  argument
       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, specifying 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 language-dependent  radix  character  in  the
       input  string.  The  radix  character  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 directive is composed of one of the following: one  or  more  white-space  characters  (
       <space>s,  <tab>s,  <newline>s,  <vertical-tab>s,  or  <form-feed>s);  an ordinary character (neither '%' nor a
       white-space character); or a conversion specification. Each conversion specification is introduced by the char-
       acter '%'  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 conversion 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 unavailability 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 equiv-
       alent, 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 directive shall fail.

       A directive that is a conversion specification defines a set of matching 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 specification 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  subse-
       quence  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 conversion 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  specifica-
       tion,  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 conversion 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 argument following  the  format  argument  that  has  not  already
       received  a  conversion  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  conversion  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 double.


       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 application 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 modifier, the
              application shall ensure that the corresponding argument 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 corresponding 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 representations for infinity and  NaN  (a  sym-
       bolic  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 terminating null character code,  which  shall  be  added
              automatically.

       If  an  l  (ell)  qualifier  is present, the input is a sequence of characters that begins in the initial shift
       state. Each character 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 con-
       verted. 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 terminating 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  corre-
              sponding  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 characters 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 char-
       acter  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 terminating null wide character, which shall be added auto-
       matically.

       The  conversion specification includes all subsequent bytes in the format string up to and including the match-
       ing 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  conver-
       sion 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  conversion  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 character 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 specification). 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 char-
       acter 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() functions. The application
              shall  ensure  that  the corresponding argument 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; otherwise, the behavior
              of the %p conversion specification is undefined.

       n      No input is consumed. The application shall ensure that the corresponding 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 conversion 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 specifica-
              tion 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 terminated.  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 current conversion specification shall terminate with an
       input failure. Otherwise, unless execution of the current conversion specification is terminated with a  match-
       ing  failure,  execution  of  the following conversion 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 <newline>s) shall be left unread unless matched by a conversion specification. The suc-
       cess of literal matches and suppressed assignments is only directly determinable via the %n conversion specifi-
       cation.

       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 characters. In
       other similar places, multi-byte characters have been permitted, but for alignment with  the  ISO/IEC 9899:1999
       standard, it has not been done here. Applications needing this could use the corresponding wide-character func-
       tions to achieve the desired results.

FUTURE DIRECTIONS
       None.

SEE ALSO
       getc(), printf(), setlocale(), strtod(),  strtol(),  strtoul(),  wcrtomb(),  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)