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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
commit3d08cd331c1adcf0d917392f7e527b3f00511748 (patch)
tree312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man3/sscanf.3
parentAdding debian version 6.7-2. (diff)
downloadmanpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz
manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.zip
Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-'\" t
-.\" Copyright (c) 1990, 1991 The Regents of the University of California.
-.\" All rights reserved.
-.\"
-.\" This code is derived from software contributed to Berkeley by
-.\" Chris Torek and the American National Standards Committee X3,
-.\" on Information Processing Systems.
-.\"
-.\" SPDX-License-Identifier: BSD-4-Clause-UC
-.\"
-.\" @(#)scanf.3 6.14 (Berkeley) 1/8/93
-.\"
-.\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
-.\" modified to resemble the GNU libio setup used in the Linux libc
-.\" used in versions 4.x (x>4) and 5 Helmut.Geyer@iwr.uni-heidelberg.de
-.\" Modified, aeb, 970121
-.\" 2005-07-14, mtk, added description of %n$ form; various text
-.\" incorporated from the GNU C library documentation ((C) The
-.\" Free Software Foundation); other parts substantially rewritten.
-.\"
-.\" 2008-06-23, mtk
-.\" Add ERRORS section.
-.\" Document the 'a' and 'm' modifiers for dynamic string allocation.
-.\"
-.TH sscanf 3 2023-12-09 "Linux man-pages 6.7"
-.SH NAME
-sscanf, vsscanf \- input string format conversion
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.B #include <stdio.h>
-.P
-.BI "int sscanf(const char *restrict " str ,
-.BI " const char *restrict " format ", ...);"
-.P
-.B #include <stdarg.h>
-.P
-.BI "int vsscanf(const char *restrict " str ,
-.BI " const char *restrict " format ", va_list " ap );
-.fi
-.P
-.RS -4
-Feature Test Macro Requirements for glibc (see
-.BR feature_test_macros (7)):
-.RE
-.P
-.BR vsscanf ():
-.nf
- _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
-.fi
-.SH DESCRIPTION
-The
-.BR sscanf ()
-family of functions scans formatted input according to
-.I format
-as described below.
-This format may contain
-.IR "conversion specifications" ;
-the results from such conversions, if any,
-are stored in the locations pointed to by the
-.I pointer
-arguments that follow
-.IR format .
-Each
-.I pointer
-argument must be of a type that is appropriate for the value returned
-by the corresponding conversion specification.
-.P
-If the number of conversion specifications in
-.I format
-exceeds the number of
-.I pointer
-arguments, the results are undefined.
-If the number of
-.I pointer
-arguments exceeds the number of conversion specifications, then the excess
-.I pointer
-arguments are evaluated, but are otherwise ignored.
-.P
-.BR sscanf ()
-These functions
-read their input from the string pointed to by
-.IR str .
-.P
-The
-.BR vsscanf ()
-function is analogous to
-.BR vsprintf (3).
-.P
-The
-.I format
-string consists of a sequence of
-.I directives
-which describe how to process the sequence of input characters.
-If processing of a directive fails, no further input is read, and
-.BR sscanf ()
-returns.
-A "failure" can be either of the following:
-.IR "input failure" ,
-meaning that input characters were unavailable, or
-.IR "matching failure" ,
-meaning that the input was inappropriate (see below).
-.P
-A directive is one of the following:
-.TP
-\[bu]
-A sequence of white-space characters (space, tab, newline, etc.; see
-.BR isspace (3)).
-This directive matches any amount of white space,
-including none, in the input.
-.TP
-\[bu]
-An ordinary character (i.e., one other than white space or \[aq]%\[aq]).
-This character must exactly match the next character of input.
-.TP
-\[bu]
-A conversion specification,
-which commences with a \[aq]%\[aq] (percent) character.
-A sequence of characters from the input is converted according to
-this specification, and the result is placed in the corresponding
-.I pointer
-argument.
-If the next item of input does not match the conversion specification,
-the conversion fails\[em]this is a
-.IR "matching failure" .
-.P
-Each
-.I conversion specification
-in
-.I format
-begins with either the character \[aq]%\[aq] or the character sequence
-"\fB%\fP\fIn\fP\fB$\fP"
-(see below for the distinction) followed by:
-.TP
-\[bu]
-An optional \[aq]*\[aq] assignment-suppression character:
-.BR sscanf ()
-reads input as directed by the conversion specification,
-but discards the input.
-No corresponding
-.I pointer
-argument is required, and this specification is not
-included in the count of successful assignments returned by
-.BR scanf ().
-.TP
-\[bu]
-For decimal conversions, an optional quote character (\[aq]).
-This specifies that the input number may include thousands'
-separators as defined by the
-.B LC_NUMERIC
-category of the current locale.
-(See
-.BR setlocale (3).)
-The quote character may precede or follow the \[aq]*\[aq]
-assignment-suppression character.
-.TP
-\[bu]
-An optional \[aq]m\[aq] character.
-This is used with string conversions
-.RI ( %s ,
-.IR %c ,
-.IR %[ ),
-and relieves the caller of the
-need to allocate a corresponding buffer to hold the input: instead,
-.BR sscanf ()
-allocates a buffer of sufficient size,
-and assigns the address of this buffer to the corresponding
-.I pointer
-argument, which should be a pointer to a
-.I "char\ *"
-variable (this variable does not need to be initialized before the call).
-The caller should subsequently
-.BR free (3)
-this buffer when it is no longer required.
-.TP
-\[bu]
-An optional decimal integer which specifies the
-.IR "maximum field width" .
-Reading of characters stops either when this maximum is reached or
-when a nonmatching character is found, whichever happens first.
-Most conversions discard initial white space characters (the exceptions
-are noted below),
-and these discarded characters don't count toward the maximum field width.
-String input conversions store a terminating null byte (\[aq]\e0\[aq])
-to mark the end of the input;
-the maximum field width does not include this terminator.
-.TP
-\[bu]
-An optional
-.IR "type modifier character" .
-For example, the
-.B l
-type modifier is used with integer conversions such as
-.B %d
-to specify that the corresponding
-.I pointer
-argument refers to a
-.I "long"
-rather than a pointer to an
-.IR int .
-.TP
-\[bu]
-A
-.I "conversion specifier"
-that specifies the type of input conversion to be performed.
-.P
-The conversion specifications in
-.I format
-are of two forms, either beginning with \[aq]%\[aq] or beginning with
-"\fB%\fP\fIn\fP\fB$\fP".
-The two forms should not be mixed in the same
-.I format
-string, except that a string containing
-"\fB%\fP\fIn\fP\fB$\fP"
-specifications can include
-.B %%
-and
-.BR %* .
-If
-.I format
-contains \[aq]%\[aq]
-specifications, then these correspond in order with successive
-.I pointer
-arguments.
-In the
-"\fB%\fP\fIn\fP\fB$\fP"
-form (which is specified in POSIX.1-2001, but not C99),
-.I n
-is a decimal integer that specifies that the converted input should
-be placed in the location referred to by the
-.IR n -th
-.I pointer
-argument following
-.IR format .
-.SS Conversions
-The following
-.I "type modifier characters"
-can appear in a conversion specification:
-.TP
-.B h
-Indicates that the conversion will be one of
-\fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, \fBX\fP, or \fBn\fP
-and the next pointer is a pointer to a
-.I short
-or
-.I unsigned short
-(rather than
-.IR int ).
-.TP
-.B hh
-As for
-.BR h ,
-but the next pointer is a pointer to a
-.I signed char
-or
-.IR "unsigned char" .
-.TP
-.B j
-As for
-.BR h ,
-but the next pointer is a pointer to an
-.I intmax_t
-or a
-.IR uintmax_t .
-This modifier was introduced in C99.
-.TP
-.B l
-Indicates either that the conversion will be one of
-\fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, \fBX\fP, or \fBn\fP
-and the next pointer is a pointer to a
-.I long
-or
-.I unsigned long
-(rather than
-.IR int ),
-or that the conversion will be one of
-\fBe\fP, \fBf\fP, or \fBg\fP
-and the next pointer is a pointer to
-.I double
-(rather than
-.IR float ).
-If used with
-.B %c
-or
-.BR %s ,
-the corresponding parameter is considered
-as a pointer to a wide character or wide-character string respectively.
-.\" This use of l was introduced in Amendment 1 to ISO C90.
-.TP
-.B ll
-(ell-ell)
-Indicates that the conversion will be one of
-.BR b ,
-.BR d ,
-.BR i ,
-.BR o ,
-.BR u ,
-.BR x ,
-.BR X ,
-or
-.B n
-and the next pointer is a pointer to a
-.I long long
-or
-.I unsigned long long
-(rather than
-.IR int ).
-.TP
-.B L
-Indicates that the conversion will be either
-\fBe\fP, \fBf\fP, or \fBg\fP
-and the next pointer is a pointer to
-.I "long double"
-or
-(as a GNU extension)
-the conversion will be
-\fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, or \fBx\fP
-and the next pointer is a pointer to
-.IR "long long" .
-.\" MTK, Jul 05: The following is no longer true for modern
-.\" ANSI C (i.e., C99):
-.\" (Note that long long is not an
-.\" ANSI C
-.\" type. Any program using this will not be portable to all
-.\" architectures).
-.TP
-.B q
-equivalent to
-.BR L .
-This specifier does not exist in ANSI C.
-.TP
-.B t
-As for
-.BR h ,
-but the next pointer is a pointer to a
-.IR ptrdiff_t .
-This modifier was introduced in C99.
-.TP
-.B z
-As for
-.BR h ,
-but the next pointer is a pointer to a
-.IR size_t .
-This modifier was introduced in C99.
-.P
-The following
-.I "conversion specifiers"
-are available:
-.TP
-.B %
-Matches a literal \[aq]%\[aq].
-That is,
-.B %\&%
-in the format string matches a
-single input \[aq]%\[aq] character.
-No conversion is done (but initial white space characters are discarded),
-and assignment does not occur.
-.TP
-.B d
-Matches an optionally signed decimal integer;
-the next pointer must be a pointer to
-.IR int .
-.\" .TP
-.\" .B D
-.\" Equivalent to
-.\" .IR ld ;
-.\" this exists only for backward compatibility.
-.\" (Note: thus only in libc4
-.\" In libc5 and glibc the
-.\" .B %D
-.\" is silently ignored, causing old programs to fail mysteriously.)
-.TP
-.B i
-Matches an optionally signed integer; the next pointer must be a pointer to
-.IR int .
-The integer is read in base 16 if it begins with
-.I 0x
-or
-.IR 0X ,
-in base 8 if it begins with
-.IR 0 ,
-and in base 10 otherwise.
-Only characters that correspond to the base are used.
-.TP
-.B o
-Matches an unsigned octal integer; the next pointer must be a pointer to
-.IR "unsigned int" .
-.TP
-.B u
-Matches an unsigned decimal integer; the next pointer must be a
-pointer to
-.IR "unsigned int" .
-.TP
-.B x
-Matches an unsigned hexadecimal integer
-(that may optionally begin with a prefix of
-.I 0x
-or
-.IR 0X ,
-which is discarded); the next pointer must
-be a pointer to
-.IR "unsigned int" .
-.TP
-.B X
-Equivalent to
-.BR x .
-.TP
-.B f
-Matches an optionally signed floating-point number; the next pointer must
-be a pointer to
-.IR float .
-.TP
-.B e
-Equivalent to
-.BR f .
-.TP
-.B g
-Equivalent to
-.BR f .
-.TP
-.B E
-Equivalent to
-.BR f .
-.TP
-.B a
-(C99) Equivalent to
-.BR f .
-.TP
-.B s
-Matches a sequence of non-white-space characters;
-the next pointer must be a pointer to the initial element of a
-character array that is long enough to hold the input sequence and
-the terminating null byte (\[aq]\e0\[aq]), which is added automatically.
-The input string stops at white space or at the maximum field
-width, whichever occurs first.
-.TP
-.B c
-Matches a sequence of characters whose length is specified by the
-.I maximum field width
-(default 1); the next pointer must be a pointer to
-.IR char ,
-and there must be enough room for all the characters
-(no terminating null byte is added).
-The usual skip of leading white space is suppressed.
-To skip white space first, use an explicit space in the format.
-.TP
-.B \&[
-Matches a nonempty sequence of characters from the specified set of
-accepted characters; the next pointer must be a pointer to
-.IR char ,
-and there must be enough room for all the characters in the string, plus a
-terminating null byte.
-The usual skip of leading white space is suppressed.
-The string is to be made up of characters in (or not in) a particular set;
-the set is defined by the characters between the open bracket
-.B [
-character and a close bracket
-.B ]
-character.
-The set
-.I excludes
-those characters if the first character after the open bracket is a
-circumflex
-.RB ( \[ha] ).
-To include a close bracket in the set, make it the first character after
-the open bracket or the circumflex; any other position will end the set.
-The hyphen character
-.B \-
-is also special; when placed between two other characters, it adds all
-intervening characters to the set.
-To include a hyphen, make it the last
-character before the final close bracket.
-For instance,
-.B [\[ha]]0\-9\-]
-means
-the set "everything except close bracket, zero through nine, and hyphen".
-The string ends with the appearance of a character not in the (or, with a
-circumflex, in) set or when the field width runs out.
-.TP
-.B p
-Matches a pointer value (as printed by
-.B %p
-in
-.BR printf (3));
-the next pointer must be a pointer to a pointer to
-.IR void .
-.TP
-.B n
-Nothing is expected; instead, the number of characters consumed thus far
-from the input is stored through the next pointer, which must be a pointer
-to
-.IR int ,
-or variant whose size matches the (optionally)
-supplied integer length modifier.
-This is
-.I not
-a conversion and does
-.I not
-increase the count returned by the function.
-The assignment can be suppressed with the
-.B *
-assignment-suppression character, but the effect on the
-return value is undefined.
-Therefore
-.B %*n
-conversions should not be used.
-.SH RETURN VALUE
-On success, these functions return the number of input items
-successfully matched and assigned;
-this can be fewer than provided for,
-or even zero, in the event of an early matching failure.
-.P
-The value
-.B EOF
-is returned if the end of input is reached before either the first
-successful conversion or a matching failure occurs.
-.SH ERRORS
-.TP
-.B EILSEQ
-Input byte sequence does not form a valid character.
-.TP
-.B EINVAL
-Not enough arguments; or
-.I format
-is NULL.
-.TP
-.B ENOMEM
-Out of memory.
-.SH ATTRIBUTES
-For an explanation of the terms used in this section, see
-.BR attributes (7).
-.TS
-allbox;
-lbx lb lb
-l l l.
-Interface Attribute Value
-T{
-.na
-.nh
-.BR sscanf (),
-.BR vsscanf ()
-T} Thread safety MT-Safe locale
-.TE
-.SH STANDARDS
-C11, POSIX.1-2008.
-.SH HISTORY
-C89, POSIX.1-2001.
-.P
-The
-.B q
-specifier is the 4.4BSD notation for
-.IR "long long" ,
-while
-.B ll
-or the usage of
-.B L
-in integer conversions is the GNU notation.
-.P
-The Linux version of these functions is based on the
-.I GNU
-.I libio
-library.
-Take a look at the
-.I info
-documentation of
-.I GNU
-.I libc (glibc-1.08)
-for a more concise description.
-.SH NOTES
-.SS The 'a' assignment-allocation modifier
-Originally, the GNU C library supported dynamic allocation for string inputs
-(as a nonstandard extension) via the
-.B a
-character.
-(This feature is present at least as far back as glibc 2.0.)
-Thus, one could write the following to have
-.BR sscanf ()
-allocate a buffer for a string,
-with a pointer to that buffer being returned in
-.IR *buf :
-.P
-.in +4n
-.EX
-char *buf;
-sscanf(str, "%as", &buf);
-.EE
-.in
-.P
-The use of the letter
-.B a
-for this purpose was problematic, since
-.B a
-is also specified by the ISO C standard as a synonym for
-.B f
-(floating-point input).
-POSIX.1-2008 instead specifies the
-.B m
-modifier for assignment allocation (as documented in DESCRIPTION, above).
-.P
-Note that the
-.B a
-modifier is not available if the program is compiled with
-.I gcc\~\-std=c99
-or
-.I gcc\~\-D_ISOC99_SOURCE
-(unless
-.B _GNU_SOURCE
-is also specified), in which case the
-.B a
-is interpreted as a specifier for floating-point numbers (see above).
-.P
-Support for the
-.B m
-modifier was added to glibc 2.7,
-and new programs should use that modifier instead of
-.BR a .
-.P
-As well as being standardized by POSIX, the
-.B m
-modifier has the following further advantages over
-the use of
-.BR a :
-.IP \[bu] 3
-It may also be applied to
-.B %c
-conversion specifiers (e.g.,
-.BR %3mc ).
-.IP \[bu]
-It avoids ambiguity with respect to the
-.B %a
-floating-point conversion specifier (and is unaffected by
-.I gcc\~\-std=c99
-etc.).
-.SH BUGS
-.SS Numeric conversion specifiers
-Use of the numeric conversion specifiers produces Undefined Behavior
-for invalid input.
-See
-.UR https://port70.net/\:%7Ensz/\:c/\:c11/\:n1570.html\:#7.21.6.2p10
-C11 7.21.6.2/10
-.UE .
-This is a bug in the ISO C standard,
-and not an inherent design issue with the API.
-However,
-current implementations are not safe from that bug,
-so it is not recommended to use them.
-Instead,
-programs should use functions such as
-.BR strtol (3)
-to parse numeric input.
-Alternatively,
-mitigate it by specifying a maximum field width.
-.SS Nonstandard modifiers
-These functions are fully C99 conformant, but provide the
-additional modifiers
-.B q
-and
-.B a
-as well as an additional behavior of the
-.B L
-and
-.B ll
-modifiers.
-The latter may be considered to be a bug, as it changes the
-behavior of modifiers defined in C99.
-.P
-Some combinations of the type modifiers and conversion
-specifiers defined by C99 do not make sense
-(e.g.,
-.BR "%Ld" ).
-While they may have a well-defined behavior on Linux, this need not
-to be so on other architectures.
-Therefore it usually is better to use
-modifiers that are not defined by C99 at all, that is, use
-.B q
-instead of
-.B L
-in combination with
-\fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, and \fBX\fP
-conversions or
-.BR ll .
-.P
-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 .
-.SH EXAMPLES
-To use the dynamic allocation conversion specifier, specify
-.B m
-as a length modifier (thus
-.B %ms
-or
-\fB%m[\fP\fIrange\fP\fB]\fP).
-The caller must
-.BR free (3)
-the returned string, as in the following example:
-.P
-.in +4n
-.EX
-char *p;
-int n;
-\&
-errno = 0;
-n = sscanf(str, "%m[a\-z]", &p);
-if (n == 1) {
- printf("read: %s\en", p);
- free(p);
-} else if (errno != 0) {
- perror("sscanf");
-} else {
- fprintf(stderr, "No matching characters\en");
-}
-.EE
-.in
-.P
-As shown in the above example, it is necessary to call
-.BR free (3)
-only if the
-.BR sscanf ()
-call successfully read a string.
-.SH SEE ALSO
-.BR getc (3),
-.BR printf (3),
-.BR setlocale (3),
-.BR strtod (3),
-.BR strtol (3),
-.BR strtoul (3)