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Faraz Vahedi
d08296c7ab
Several standard library functions are specified to return an unqualified pointer while accepting a pointer to a potentially const-qualified object. N3020 addresses this behaviour, discarding qualifiers due to incompatible pointer types, by introducing qualifier-preserving macros for the affected set of standard library functions. Add `__qualsel()` helper to `<sys/cdefs.h>`, implemented using the generic selection, and define qualifier-preserving macros for that set of functions in `<string.h>`, `<wchar.h>`, and `<stdlib.h>`. Macros are gated on `_STDC_VERSION__ >= 202311L && !__cplusplus`, therefore there is no behavioural change for earlier C modes or C++ translation units. The kernel is likewise unaffected, as it does not include userland headers. As function-like macros, they are transparent except at a call site where the address-of operator is applied, the macro is suppressed via `#undef`, or the identifier appears in parenthesised form; all of which cause the underlying function designator to be used instead. Reviewed by: fuz Approved by: fuz (mentor) MFC after: 1 month Pull Request: https://github.com/freebsd/freebsd-src/pull/2288
131 lines
3.4 KiB
Plaintext
131 lines
3.4 KiB
Plaintext
.\" 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. 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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.Dd June 21, 2026
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.Dt STRCHR 3
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.Os
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.Sh NAME
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.Nm strchr , strrchr , strchrnul
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.Nd locate character in string
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft "char *"
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.Fn strchr "const char *s" "int c"
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.Ft "char *"
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.Fn strrchr "const char *s" "int c"
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.Ft "char *"
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.Fn strchrnul "const char *s" "int c"
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.Sh DESCRIPTION
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The
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.Fn strchr
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function locates the first occurrence of
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.Fa c
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(converted to a
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.Vt char )
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in the string pointed to by
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.Fa s .
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The terminating null character is considered part of the string;
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therefore if
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.Fa c
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is
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.Ql \e0 ,
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the functions locate the terminating
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.Ql \e0 .
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.Pp
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The
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.Fn strrchr
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function is identical to
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.Fn strchr
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except it locates the last occurrence of
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.Fa c .
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.Pp
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The
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.Fn strchrnul
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function is identical to
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.Fn strchr
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except that if
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.Fa c
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is not found in
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.Fa s
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a pointer to the terminating
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.Ql \e0
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is returned.
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.Sh RETURN VALUES
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The functions
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.Fn strchr
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and
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.Fn strrchr
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return a pointer to the located character, or
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.Dv NULL
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if the character does not appear in the string.
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.Pp
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.Fn strchrnul
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returns a pointer to the terminating
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.Ql \e0
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if the character does not appear in the string.
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.Sh SEE ALSO
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.Xr memchr 3 ,
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.Xr memmem 3 ,
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.Xr strcspn 3 ,
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.Xr strpbrk 3 ,
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.Xr strsep 3 ,
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.Xr strspn 3 ,
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.Xr strstr 3 ,
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.Xr strtok 3 ,
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.Xr wcschr 3
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.Sh STANDARDS
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The functions
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.Fn strchr
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and
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.Fn strrchr
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conform to
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.St -isoC-2023 ,
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where they are specified as qualifier-preserving functions.
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.Pp
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The function
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.Fn strchrnul
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is a
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.Tn GNU
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extension.
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Like the qualifier-preserving functions in
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.St -isoC-2023 ,
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.Fx
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implements
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.Fn strchrnul
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as qualifier-preserving as well.
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.Sh HISTORY
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The
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.Fn strchrnul
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function first appeared in glibc 2.1.1 and was added in
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.Fx 10.0 .
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