memchr

MEMCHR(3)                  Linux Programmer's Manual                 MEMCHR(3)



NAME
       memchr, memrchr, rawmemchr - scan memory for a character

SYNOPSIS
       #include <string.h>

       void *memchr(const void *s, int c, size_t n);

       void *memrchr(const void *s, int c, size_t n);

       void *rawmemchr(const void *s, int c);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       memrchr(), rawmemchr(): _GNU_SOURCE

DESCRIPTION
       The memchr() function scans the initial n bytes of the memory area
       pointed to by s for the first instance of c.  Both c and the bytes of
       the memory area pointed to by s are interpreted as unsigned char.

       The memrchr() function is like the memchr() function, except that it
       searches backward from the end of the n bytes pointed to by s instead
       of forward from the beginning.

       The rawmemchr() function is similar to memchr(): it assumes (i.e., the
       programmer knows for certain) that an instance of c lies somewhere in
       the memory area starting at the location pointed to by s, and so
       performs an optimized search for c (i.e., no use of a count argument to
       limit the range of the search).  If an instance of c is not found, the
       results are unpredictable.  The following call is a fast means of
       locating a string's terminating null byte:

           char *p = rawmemchr(s, '\0');

RETURN VALUE
       The memchr() and memrchr() functions return a pointer to the matching
       byte or NULL if the character does not occur in the given memory area.

       The rawmemchr() function returns a pointer to the matching byte, if one
       is found.  If no matching byte is found, the result is unspecified.

VERSIONS
       rawmemchr() first appeared in glibc in version 2.1.

       memrchr() first appeared in glibc in version 2.2.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       ┌─────────────────────────────────┬───────────────┬─────────┐
       │Interface                        Attribute     Value   │
       ├─────────────────────────────────┼───────────────┼─────────┤
       │memchr(), memrchr(), rawmemchr() │ Thread safety │ MT-Safe │
       └─────────────────────────────────┴───────────────┴─────────┘
CONFORMING TO
       memchr(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

       The memrchr() function is a GNU extension, available since glibc
       2.1.91.

       The rawmemchr() function is a GNU extension, available since glibc 2.1.

SEE ALSO
       bstring(3), ffs(3), index(3), memmem(3), rindex(3), strchr(3),
       strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wmemchr(3)

COLOPHON
       This page is part of release 5.06 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



                                  2019-03-06                         MEMCHR(3)