mirror of https://github.com/mkerrisk/man-pages
587 lines
16 KiB
Groff
587 lines
16 KiB
Groff
.\" Copyright (c) 1990, 1991 The Regents of the University of California.
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.\" 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 6.14 (Berkeley) 1/8/93
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.\"
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.\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
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.\" modified to resemble the GNU libio setup used in the Linux libc
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.\" used in versions 4.x (x>4) and 5 Helmut.Geyer@iwr.uni-heidelberg.de
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.\" Modified, aeb, 970121
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.\" 2005-07-14, mtk, added description of %n$ form; various text
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.\" incorporated from the GNU C library documentation ((C) The
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.\" Free Software Foundation); other parts substantially rewritten.
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.\"
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.TH SCANF 3 1995-11-01 "LINUX MANPAGE" "Linux Programmer's Manual"
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.SH NAME
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scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf \- input format conversion
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.SH SYNOPSIS
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.nf
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.B #include <stdio.h>
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.na
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.BI "int scanf(const char *" format ", ..." );
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.br
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.BI "int fscanf(FILE *" stream ", const char *" format ", ..." );
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.br
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.BI "int sscanf(const char *" str ", const char *" format ", ..." );
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.sp
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.B #include <stdarg.h>
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.BI "int vscanf(const char *" format ", va_list " ap );
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.br
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.BI "int vsscanf(const char *" str ", const char *" format ", va_list " ap );
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.br
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.BI "int vfscanf(FILE *" stream ", const char *" format ", va_list " ap );
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.ad
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.SH DESCRIPTION
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The
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.BR scanf ()
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family of functions scans input according to
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.I format
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as described below. This format may contain
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.IR "conversion specifications" ;
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the results from such conversions, if any,
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are stored in the locations pointed to by the
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.I pointer
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arguments that follow
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.IR format .
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Each
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.I pointer
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argument must be of a type that is appropriate for the value returned
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by the corresponding conversion specification.
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If the number of conversion specifications in
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.I format
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exceeds the number of
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.I pointer
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arguments, the results are undefined.
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If the number of
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.I pointer
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arguments exceeds the number of conversion specifications, then the excess
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.I pointer
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arguments are evaluated, but are otherwise ignored.
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The
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.BR scanf ()
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function reads input from the standard input stream
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.IR stdin ,
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.BR fscanf ()
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reads input from the stream pointer
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.IR stream ,
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and
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.BR sscanf ()
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reads its input from the character string pointed to by
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.IR str .
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.PP
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The
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.BR vfscanf ()
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function is analogous to
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.BR vfprintf (3)
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and reads input from the stream pointer
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.I stream
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using a variable argument list of pointers (see
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.BR stdarg (3).
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The
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.BR vscanf ()
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function scans a variable argument list from the standard input and the
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.BR vsscanf ()
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function scans it from a string; these are analogous to the
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.BR vprintf ()
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and
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.BR vsprintf ()
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functions respectively.
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.PP
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The
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.I format
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string consists of a sequence of
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.IR directives
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which describe how to process the sequence of input characters.
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If processing of a directive fails, no further input is read, and
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.BR scanf ()
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returns.
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A "failure" can be either of the following:
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.IR "input failure" ,
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meaning that input characters were unavailable, or
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.IR "matching failure" ,
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meaning that the input was inappropriate (see below).
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A directive is one of the following:
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.TP
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\(bu
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A sequence of white-space characters (space, tab, newline, etc; see
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.BR isspace (3)).
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This directive matches any amount of white space,
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including none, in the input.
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.TP
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\(bu
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An ordinary character (i.e., one other than white space or '%').
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This character must exactly match the next character of input.
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.TP
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\(bu
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A conversion specification, which commences with a '%' (percent) character.
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A sequence of characters from the input is converted according to
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this specification, and the result is placed in the corresponding
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.I pointer
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argument.
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If the next item of input does not match the the conversion specification,
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the conversion fails \(em this is a
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.IR "matching failure" .
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.PP
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Each
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.I conversion specification
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in
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.I format
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begins with either the character '%' or the character sequence
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"\fB%\fP\fIn\fP\fB$\fP"
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(see below for the distinction) followed by:
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.TP
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\(bu
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An optional '*' assignment-suppression character:
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.BR scanf ()
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reads input as directed by the conversion specification,
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but discards the input.
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No corresponding
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.I pointer
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argument is required, and this specification is not
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included in the count of successful assignments returned by
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.BR scanf ().
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.TP
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\(bu
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An optional 'a' character.
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This is used with string conversions, and relieves the caller of the
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need to allocate a corresponding buffer to hold the input: instead,
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.BR scanf ()
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allocates a buffer of sufficient size,
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and assigns the address of this buffer to the corresponding
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.I pointer
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argument, which should be a pointer to a
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.I "char *"
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variable (this variable does not need to be initialised before the call).
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The caller should subsequently
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.BR free (3)
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this buffer when it is no longer required.
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This is a GNU extension;
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C99 employs the 'a' character as a conversion specifier (and
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it can also be used as such in the GNU implementation).
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.TP
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\(bu
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An optional decimal integer which specifies the
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.IR "maximum field width" .
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Reading of characters stops either when this maximum is reached or
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when a non-matching character is found, whichever happens first.
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Most conversions discard initial whitespace characters (the exceptions
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are noted below),
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and these discarded characters don't count towards the maximum field width.
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String input conversions store a null terminator ('\\0')
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to mark the end of the input;
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the maximum field width does not include this terminator.
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.TP
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\(bu
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An optional
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.IR "type modifier character" .
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For example, the
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.B l
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type modifier is used with integer conversions such as
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.I %d
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to specify that the corresponding
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.I pointer
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argument refers to a
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.I "long int"
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rather than a pointer to an
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.IR int .
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.TP
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\(bu
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A
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.I "conversion specifier"
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that specifies the type of input conversion to be performed.
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.PP
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The conversion specifications in
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.I format
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are of two forms, either beginning with '%' or beginning with
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"\fB%\fP\fIn\fP\fB$\fP".
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The two forms should not be mixed in the same
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.I format
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string, except that a string containing
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"\fB%\fP\fIn\fP\fB$\fP"
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specifications can include
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.I %%
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and
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.IR %* .
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If
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.I format
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contains '%'
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specifications then these correspond in order with successive
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.I pointer
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arguments.
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In the
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"\fB%\fP\fIn\fP\fB$\fP"
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form (which is specified in SUSv3, but not C99),
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.I n
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is a decimal integer that specifies that the converted input should
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be placed in the location referred to by the
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.IR n -th
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.I pointer
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argument following
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.IR format .
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.SH CONVERSIONS
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The following
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.IR "type modifier characters"
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can appear in a conversion specification:
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.TP
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.B h
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Indicates that the conversion will be one of
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.B diouxX
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or
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.B n
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and the next pointer is a pointer to a
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.I short int
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or
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.I unsigned short int
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(rather than
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.IR int ).
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.TP
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.B hh
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As for
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.BR h ,
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but the next pointer is a pointer to a
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.I signed char
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or
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.IR "unsigned char" .
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.TP
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.B j
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As for
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.BR h ,
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but the next pointer is a pointer to a
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.I intmax_t
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or
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.IR uintmax_t .
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This modifier was introduced in C99.
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.TP
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.B l
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Indicates either that the conversion will be one of
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.B diouxX
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or
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.B n
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and the next pointer is a pointer to a
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.I long int
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or
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.I unsigned long int
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(rather than
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.IR int ),
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or that the conversion will be one of
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.B efg
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and the next pointer is a pointer to
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.I double
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(rather than
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.IR float ).
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Specifying two
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.B l
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characters is equivalent to
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.BR L .
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If used with
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.I %c
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or
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.I %s
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the corresponding parameter is considered
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as a pointer to a wide character or wide character string respectively.
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.\" This use of l was introduced in Amendment 1 to ISO C90.
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.TP
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.B L
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Indicates that the conversion will be either
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.B efg
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and the next pointer is a pointer to
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.IR "long double"
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or the conversion will be
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.B dioux
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and the next pointer is a pointer to
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.IR "long long" .
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.\" MTK, Jul 05: The following is no longer true for modern
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.\" ANSI C (i.e., C99):
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.\" (Note that long long is not an
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.\" ANSI C
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.\" type. Any program using this will not be portable to all
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.\" architectures).
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.TP
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.B q
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equivalent to
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.BR L .
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This specifier does not exist in ANSI C.
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.TP
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.B t
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As for
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.BR h ,
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but the next pointer is a pointer to a
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.IR ptrdiff_t .
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This modifier was introduced in C99.
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.TP
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.B z
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As for
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.BR h ,
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but the next pointer is a pointer to a
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.IR size_t .
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This modifier was introduced in C99.
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.PP
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The following
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.I "conversion specifiers"
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are available:
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.TP
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.B %
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Matches a literal '%'. That is,
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.I %\&%
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in the format string matches a
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single input '%' character. No conversion is done, and assignment does not
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occur.
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.TP
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.B 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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.IR int .
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.TP
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.B D
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Equivalent to
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.IR ld ;
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this exists only for backwards compatibility.
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(Note: thus only in libc4. In libc5 and glibc the
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.I %D
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is silently ignored, causing old programs to fail mysteriously.)
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.TP
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.B i
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Matches an optionally signed integer; the next pointer must be a pointer to
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.IR int .
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The integer is read in base 16 if it begins with
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.I 0x
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or
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.IR 0X ,
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in base 8 if it begins with
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.IR 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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.TP
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.B o
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Matches an unsigned octal integer; the next pointer must be a pointer to
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.IR "unsigned int" .
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.TP
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.B u
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Matches an unsigned decimal integer; the next pointer must be a
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pointer to
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.IR "unsigned int" .
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.TP
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.B x
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Matches an unsigned hexadecimal integer; the next pointer must
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be a pointer to
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.IR "unsigned int" .
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.TP
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.B X
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Equivalent to
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.BR x .
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.TP
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.B f
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Matches an optionally signed floating-point number; the next pointer must
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be a pointer to
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.IR float .
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.TP
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.B e
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Equivalent to
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.BR f .
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.TP
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.B g
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Equivalent to
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.BR f .
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.TP
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.B E
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Equivalent to
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.BR f .
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.TP
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.B a
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(C99) Equivalent to
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.BR f .
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.TP
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.B 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 character array that is
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long enough to hold the input sequence and the terminating null
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character ('\\0'), which is added automatically.
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The input string stops at white space or at the maximum field
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|
width, whichever occurs first.
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.TP
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.B c
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Matches a sequence of characters whose length is specified by the
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.I maximum field width
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(default 1); the next pointer must be a pointer to
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.IR char ,
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and there must be enough room for all the characters (no terminating
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null byte
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is added). The usual skip of leading white space is suppressed. To skip
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white space first, use an explicit space in the format.
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.TP
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.B \&[
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Matches a nonempty sequence of characters from the specified set of
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accepted characters; the next pointer must be a pointer to
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.IR char ,
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|
and there must be enough room for all the characters in the string, plus a
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terminating null byte.
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The usual skip of leading white space is suppressed. The
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string is to be made up of characters in (or not in) a particular set; the
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set is defined by the characters between the open bracket
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.B [
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character and a close bracket
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.B ]
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|
character. The set
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.I excludes
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those characters if the first character after the open bracket is a
|
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circumflex
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.RB ( ^ ).
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|
To include a close bracket in the set, make it the first character after
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the open bracket or the circumflex; any other position will end the set.
|
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The hyphen character
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.B \-
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is also special; when placed between two other characters, it adds all
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intervening characters to the set. To include a hyphen, make it the last
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character before the final close bracket. For instance,
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.B [^]0\-9\-]
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means
|
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the set "everything except close bracket, zero through nine, and hyphen".
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|
The string ends with the appearance of a character not in the (or, with a
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circumflex, in) set or when the field width runs out.
|
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.TP
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.B p
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|
Matches a pointer value (as printed by
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.I %p
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in
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.BR printf (3);
|
|
the next pointer must be a pointer to a pointer to
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.IR void .
|
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.TP
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.B n
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Nothing is expected; instead, the number of characters consumed thus far
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from the input is stored through the next pointer, which must be a pointer
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to
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.IR int .
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This is
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.I not
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a conversion, although it can be suppressed with the
|
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.B *
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assignment-suppression character.
|
|
The C standard says: "Execution of a
|
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.I %n
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directive does not increment
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the assignment count returned at the completion of execution"
|
|
but the Corrigendum seems to contradict this. Probably it is wise
|
|
not to make any assumptions on the effect of
|
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.I %n
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|
conversions on the return value.
|
|
.SH "RETURN VALUE"
|
|
These functions return the number of input items
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successfully matched and assigned,
|
|
which can be fewer than provided for,
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or even zero in the event of an early matching failure.
|
|
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|
The value
|
|
.B EOF
|
|
is returned if the end of input is reached before either the first
|
|
successful conversion or a matching failure occurs.
|
|
.B EOF
|
|
is also returned if a read error occurs,
|
|
in which case the error indicator for the stream (see
|
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.BR ferror (3))
|
|
is set, and
|
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.I errno
|
|
is set indicate the error.
|
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.SH "SEE ALSO"
|
|
.BR getc (3),
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.BR printf (3),
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|
.BR setlocale (3),
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|
.BR strtod (3),
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|
.BR strtol (3),
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|
.BR strtoul (3)
|
|
.SH "CONFORMING TO"
|
|
The functions
|
|
.BR fscanf (),
|
|
.BR scanf (),
|
|
and
|
|
.BR sscanf ()
|
|
conform to ANSI X3.159-1989 (``ANSI C'').
|
|
.PP
|
|
The
|
|
.B q
|
|
specifier is the 4.4BSD notation for
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|
.IR "long long" ,
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|
while
|
|
.B ll
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|
or the usage of
|
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.B L
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|
in integer conversions is the GNU notation.
|
|
.PP
|
|
The Linux version of these functions is based on the
|
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.I GNU
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|
.I libio
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|
library. Take a look at the
|
|
.I info
|
|
documentation of
|
|
.I GNU
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|
.I libc (glibc-1.08)
|
|
for a more concise description.
|
|
.SH BUGS
|
|
All functions are fully ANSI X3.159-1989 conformant, but provide the
|
|
additional specifiers
|
|
.B q
|
|
and
|
|
.B a
|
|
as well as an additional behaviour of the
|
|
.B L
|
|
and
|
|
.B l
|
|
specifiers. The latter may be considered to be a bug, as it changes the
|
|
behaviour of specifiers defined in ANSI X3.159-1989.
|
|
.PP
|
|
Some combinations of the type modifiers and conversion
|
|
specifiers defined by ANSI C do not make sense
|
|
(e.g.
|
|
.BR "%Ld" ).
|
|
While they may have a well-defined behaviour on Linux, this need not
|
|
to be so on other architectures. Therefore it usually is better to use
|
|
modifiers that are not defined by ANSI C at all, i.e. use
|
|
.B q
|
|
instead of
|
|
.B L
|
|
in combination with
|
|
.B diouxX
|
|
conversions or
|
|
.BR ll .
|
|
.PP
|
|
The usage of
|
|
.B q
|
|
is not the same as on 4.4BSD,
|
|
as it may be used in float conversions equivalently to
|
|
.BR L .
|