431 lines
10 KiB
Groff
431 lines
10 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)scanf.3 8.2 (Berkeley) 12/11/93
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.\"
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.Dd December 11, 1993
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.Dt SCANF 3
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.Os
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.Sh NAME
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.Nm scanf ,
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.Nm fscanf ,
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.Nm sscanf ,
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.Nm vscanf ,
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.Nm vsscanf ,
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.Nm vfscanf
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.Nd input format conversion
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.Sh SYNOPSIS
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.Fd #include <stdio.h>
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.Ft int
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.Fn scanf "const char *format" ...
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.Ft int
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.Fn fscanf "FILE *stream" "const char *format" ...
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.Ft int
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.Fn sscanf "const char *str" "const char *format" ...
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.Fd #include <stdarg.h>
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.Ft int
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.Fn vscanf "const char *format" "va_list ap"
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.Ft int
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.Fn vsscanf "const char *str" "const char *format" "va_list ap"
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.Ft int
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.Fn vfscanf "FILE *stream" "const char *format" "va_list ap"
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.Sh DESCRIPTION
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The
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.Fn scanf
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family of functions scans input according to a
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.Fa format
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as described below.
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This format may contain
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.Em conversion specifiers ;
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the results from such conversions, if any,
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are stored through the
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.Em pointer
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arguments.
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The
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.Fn scanf
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function
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reads input from the standard input stream
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.Em stdin ,
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.Fn fscanf
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reads input from the stream pointer
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.Fa stream ,
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and
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.Fn sscanf
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reads its input from the character string pointed to by
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.Fa str .
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The
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.Fn vfscanf
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function
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is analogous to
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.Xr vfprintf 3
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and reads input from the stream pointer
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.Fa stream
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using a variable argument list of pointers (see
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.Xr stdarg 3 ) .
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The
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.Fn vscanf
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function scans a variable argument list from the standard input and
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the
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.Fn vsscanf
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function scans it from a string;
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these are analogous to
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the
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.Fn vprintf
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and
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.Fn vsprintf
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functions respectively.
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Each successive
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.Em pointer
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argument must correspond properly with
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each successive conversion specifier
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(but see `suppression' below).
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All conversions are introduced by the
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.Cm %
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(percent sign) character.
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The
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.Fa format
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string
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may also contain other characters.
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White space (such as blanks, tabs, or newlines) in the
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.Fa format
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string match any amount of white space, including none, in the input.
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Everything else
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matches only itself.
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Scanning stops
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when an input character does not match such a format character.
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Scanning also stops
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when an input conversion cannot be made (see below).
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.Sh CONVERSIONS
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Following the
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.Cm %
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character introducing a conversion
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there may be a number of
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.Em flag
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characters, as follows:
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.Bl -tag -width indent
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.It Cm *
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Suppresses assignment.
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The conversion that follows occurs as usual, but no pointer is used;
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the result of the conversion is simply discarded.
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.It Cm h
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Indicates that the conversion will be one of
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.Cm dioux
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or
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.Cm n
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and the next pointer is a pointer to a
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.Em short int
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(rather than
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.Em int ) .
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.It Cm l
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Indicates either that the conversion will be one of
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.Cm dioux
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or
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.Cm n
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and the next pointer is a pointer to a
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.Em long int
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(rather than
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.Em int ) ,
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or that the conversion will be one of
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.Cm efg
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and the next pointer is a pointer to
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.Em double
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(rather than
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.Em float ) .
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.It Cm L
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Indicates that the conversion will be
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.Cm efg
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and the next pointer is a pointer to
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.Em long double .
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(This type is not implemented; the
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.Cm L
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flag is currently ignored.)
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.El
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.Pp
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In addition to these flags,
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there may be an optional maximum field width,
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expressed as a decimal integer,
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between the
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.Cm %
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and the conversion.
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If no width is given,
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a default of `infinity' is used (with one exception, below);
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otherwise at most this many characters are scanned
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in processing the conversion.
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Before conversion begins,
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most conversions skip white space;
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this white space is not counted against the field width.
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.Pp
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The following conversions are available:
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.Bl -tag -width XXXX
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.It Cm %
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Matches a literal `%'.
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That is, `%\&%' in the format string
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matches a single input `%' character.
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No conversion is done, and assignment does not occur.
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.It Cm d
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Matches an optionally signed decimal integer;
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the next pointer must be a pointer to
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.Em int .
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.It Cm D
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Equivalent to
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.Cm ld ;
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this exists only for backwards compatibility.
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.It Cm i
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Matches an optionally signed integer;
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the next pointer must be a pointer to
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.Em int .
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The integer is read in base 16 if it begins
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with
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.Ql 0x
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or
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.Ql 0X ,
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in base 8 if it begins with
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.Ql 0 ,
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and in base 10 otherwise.
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Only characters that correspond to the base are used.
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.It Cm o
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Matches an octal integer;
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the next pointer must be a pointer to
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.Em unsigned int .
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.It Cm O
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Equivalent to
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.Cm lo ;
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this exists for backwards compatibility.
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.It Cm u
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Matches an optionally signed decimal integer;
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the next pointer must be a pointer to
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.Em unsigned int .
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.It Cm x
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Matches an optionally signed hexadecimal integer;
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the next pointer must be a pointer to
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.Em unsigned int .
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.It Cm X
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Equivalent to
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.Cm lx ;
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this violates the
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.St -ansiC ,
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but is backwards compatible with previous
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.Ux
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systems.
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.It Cm f
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Matches an optionally signed floating-point number;
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the next pointer must be a pointer to
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.Em float .
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.It Cm e
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Equivalent to
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.Cm f .
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.It Cm g
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Equivalent to
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.Cm f .
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.It Cm E
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Equivalent to
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.Cm lf ;
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this violates the
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.St -ansiC ,
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but is backwards compatible with previous
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.Ux
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systems.
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.It Cm F
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Equivalent to
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.Cm lf ;
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this exists only for backwards compatibility.
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.It Cm s
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Matches a sequence of non-white-space characters;
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the next pointer must be a pointer to
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.Em char ,
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and the array must be large enough to accept all the sequence and the
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terminating
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.Dv NUL
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character.
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The input string stops at white space
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or at the maximum field width, whichever occurs first.
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.It Cm c
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Matches a sequence of
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.Em width
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count
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characters (default 1);
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the next pointer must be a pointer to
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.Em char ,
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and there must be enough room for all the characters
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(no terminating
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.Dv NUL
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is added).
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The usual skip of leading white space is suppressed.
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To skip white space first, use an explicit space in the format.
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.It Cm \&[
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Matches a nonempty sequence of characters from the specified set
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of accepted characters;
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the next pointer must be a pointer to
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.Em char ,
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and there must be enough room for all the characters in the string,
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plus a terminating
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.Dv NUL
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character.
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The usual skip of leading white space is suppressed.
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The string is to be made up of characters in
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(or not in)
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a particular set;
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the set is defined by the characters between the open bracket
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.Cm [
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character
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and a close bracket
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.Cm ]
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character.
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The set
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.Em excludes
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those characters
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if the first character after the open bracket is a circumflex
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.Cm ^ .
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To include a close bracket in the set,
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make it the first character after the open bracket
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or the circumflex;
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any other position will end the set.
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The hyphen character
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.Cm -
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is also special;
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when placed between two other characters,
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it adds all intervening characters to the set.
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To include a hyphen,
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make it the last character before the final close bracket.
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For instance,
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.Ql [^]0-9-]
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means the set `everything except close bracket, zero through nine,
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and hyphen'.
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The string ends with the appearance of a character not in the
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(or, with a circumflex, in) set
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or when the field width runs out.
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.It Cm p
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Matches a pointer value (as printed by
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.Ql %p
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in
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.Xr printf 3 ) ;
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the next pointer must be a pointer to
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.Em void .
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.It Cm n
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Nothing is expected;
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instead, the number of characters consumed thus far from the input
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is stored through the next pointer,
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which must be a pointer to
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.Em int .
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This is
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.Em not
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a conversion, although it can be suppressed with the
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.Cm *
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flag.
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.El
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.Pp
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For backwards compatibility,
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other conversion characters (except
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.Ql \e0 )
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are taken as if they were
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.Ql %d
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or, if uppercase,
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.Ql %ld ,
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and a `conversion' of
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.Ql %\e0
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causes an immediate return of
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.Dv EOF .
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The
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.Cm F
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and
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.Cm X
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conversions will be changed in the future
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to conform to the
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.Tn ANSI
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C standard,
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after which they will act like
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.Cm f
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and
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.Cm x
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respectively.
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.Pp
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.Sh RETURN VALUES
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These
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functions
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return
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the number of input items assigned, which can be fewer than provided
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for, or even zero, in the event of a matching failure.
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Zero
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indicates that, while there was input available,
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no conversions were assigned;
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typically this is due to an invalid input character,
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such as an alphabetic character for a
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.Ql %d
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conversion.
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The value
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.Dv EOF
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is returned if an input failure occurs before any conversion such as an
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end-of-file occurs. If an error or end-of-file occurs after conversion
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has begun,
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the number of conversions which were successfully completed is returned.
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.Sh SEE ALSO
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.Xr getc 3 ,
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.Xr printf 3 ,
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.Xr strtod 3 ,
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.Xr strtol 3 ,
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.Xr strtoul 3
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.Sh STANDARDS
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The functions
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.Fn fscanf ,
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.Fn scanf ,
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and
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.Fn sscanf
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conform to
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.St -ansiC .
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.Sh HISTORY
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The functions
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.Fn vscanf ,
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.Fn vsscanf
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and
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.Fn vfscanf
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are new to this release.
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.Sh BUGS
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The current situation with
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.Cm %F
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and
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.Cm %X
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conversions is unfortunate.
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.Pp
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All of the backwards compatibility formats will be removed in the future.
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.Pp
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Numerical strings are truncated to 512 characters; for example,
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.Cm %f
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and
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.Cm %d
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are implicitly
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.Cm %512f
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and
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.Cm %512d .
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