memchr(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON

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

NAME         top

       memchr, memrchr, rawmemchr - scan memory for a character

SYNOPSIS         top

       #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         top

       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         top

       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         top

       rawmemchr() first appeared in glibc in version 2.1.

       memrchr() first appeared in glibc in version 2.2.

ATTRIBUTES         top

       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         top

       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         top

       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         top

       This page is part of release 5.11 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/.

                               2021-03-22                      MEMCHR(3)

Pages that refer to this page: bstring(3)ffs(3)index(3)strchr(3)strpbrk(3)strsep(3)strspn(3)strstr(3)strtok(3)wmemchr(3)signal-safety(7)