1MEMCHR(3) Linux Programmer's Manual MEMCHR(3)
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6 memchr, memrchr, rawmemchr - scan memory for a character
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9 #include <string.h>
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11 void *memchr(const void *s, int c, size_t n);
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13 void *memrchr(const void *s, int c, size_t n);
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15 void *rawmemchr(const void *s, int c);
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17 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19 memrchr(), rawmemchr(): _GNU_SOURCE
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22 The memchr() function scans the initial n bytes of the memory area
23 pointed to by s for the first instance of c. Both c and the bytes of
24 the memory area pointed to by s are interpreted as unsigned char.
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26 The memrchr() function is like the memchr() function, except that it
27 searches backward from the end of the n bytes pointed to by s instead
28 of forward from the beginning.
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30 The rawmemchr() function is similar to memchr(): it assumes (i.e., the
31 programmer knows for certain) that an instance of c lies somewhere in
32 the memory area starting at the location pointed to by s, and so per‐
33 forms an optimized search for c (i.e., no use of a count argument to
34 limit the range of the search). If an instance of c is not found, the
35 results are unpredictable. The following call is a fast means of
36 locating a string's terminating null byte:
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38 char *p = rawmemchr(s, '\0');
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41 The memchr() and memrchr() functions return a pointer to the matching
42 byte or NULL if the character does not occur in the given memory area.
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44 The rawmemchr() function returns a pointer to the matching byte, if one
45 is found. If no matching byte is found, the result is unspecified.
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48 rawmemchr() first appeared in glibc in version 2.1.
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50 memrchr() first appeared in glibc in version 2.2.
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53 For an explanation of the terms used in this section, see
54 attributes(7).
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56 ┌─────────────────────────────────┬───────────────┬─────────┐
57 │Interface │ Attribute │ Value │
58 ├─────────────────────────────────┼───────────────┼─────────┤
59 │memchr(), memrchr(), rawmemchr() │ Thread safety │ MT-Safe │
60 └─────────────────────────────────┴───────────────┴─────────┘
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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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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74 This page is part of release 5.04 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 2019-03-06 MEMCHR(3)