1MEMCHR(3)                  Linux Programmer's Manual                 MEMCHR(3)
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NAME

6       memchr, memrchr, rawmemchr - scan memory for a character
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SYNOPSIS

9       #include <string.h>
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11       void *memchr(const void *s, int c, size_t n);
12       void *memrchr(const void *s, int c, size_t n);
13       void *rawmemchr(const void *s, int c);
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15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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17       memrchr(), rawmemchr():
18           _GNU_SOURCE
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DESCRIPTION

21       The  memchr()  function  scans  the  initial n bytes of the memory area
22       pointed to by s for the first instance of c.  Both c and the  bytes  of
23       the memory area pointed to by s are interpreted as unsigned char.
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25       The  memrchr()  function  is like the memchr() function, except that it
26       searches backward from the end of the n bytes pointed to by  s  instead
27       of forward from the beginning.
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29       The  rawmemchr() function is similar to memchr(): it assumes (i.e., the
30       programmer knows for certain) that an instance of c lies  somewhere  in
31       the  memory  area starting at the location pointed to by s, and so per‐
32       forms an optimized search for c (i.e., no use of a  count  argument  to
33       limit  the range of the search).  If an instance of c is not found, the
34       results are unpredictable.  The following call is a fast means  of  lo‐
35       cating a string's terminating null byte:
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37           char *p = rawmemchr(s, '\0');
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RETURN VALUE

40       The  memchr()  and memrchr() functions return a pointer to the matching
41       byte or NULL if the character does not occur in the given memory area.
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43       The rawmemchr() function returns a pointer to the matching byte, if one
44       is found.  If no matching byte is found, the result is unspecified.
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VERSIONS

47       rawmemchr() first appeared in glibc in version 2.1.
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49       memrchr() first appeared in glibc in version 2.2.
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ATTRIBUTES

52       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
53       tributes(7).
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55       ┌────────────────────────────────────────────┬───────────────┬─────────┐
56       │Interface                                   │ Attribute     │ Value   │
57       ├────────────────────────────────────────────┼───────────────┼─────────┤
58       │memchr(), memrchr(), rawmemchr()            │ Thread safety │ MT-Safe │
59       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

62       memchr(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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64       The memrchr() function  is  a  GNU  extension,  available  since  glibc
65       2.1.91.
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67       The rawmemchr() function is a GNU extension, available since glibc 2.1.
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SEE ALSO

70       bstring(3),  ffs(3),  index(3),  memmem(3), rindex(3), strchr(3), strp‐
71       brk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wmemchr(3)
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COLOPHON

74       This page is part of release 5.12 of the Linux  man-pages  project.   A
75       description  of  the project, information about reporting bugs, and the
76       latest    version    of    this    page,    can     be     found     at
77       https://www.kernel.org/doc/man-pages/.
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81                                  2021-03-22                         MEMCHR(3)
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