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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)
2021-03-22 MEMCHR(3)