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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | CAVEATS | SEE ALSO | COLOPHON |
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memcmp(3) Library Functions Manual memcmp(3)
memcmp - compare memory areas
Standard C library (libc, -lc)
#include <string.h>
int memcmp(const void s1[.n], const void s2[.n], size_t n);
The memcmp() function compares the first n bytes (each interpreted
as unsigned char) of the memory areas s1 and s2.
The memcmp() function returns an integer less than, equal to, or
greater than zero if the first n bytes of s1 is found,
respectively, to be less than, to match, or be greater than the
first n bytes of s2.
For a nonzero return value, the sign is determined by the sign of
the difference between the first pair of bytes (interpreted as
unsigned char) that differ in s1 and s2.
If n is zero, the return value is zero.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ memcmp() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
POSIX.1-2001, C89, SVr4, 4.3BSD.
Do not use memcmp() to compare confidential data, such as
cryptographic secrets, because the CPU time required for the
comparison depends on the contents of the addresses compared, this
function is subject to timing-based side-channel attacks. In such
cases, a function that performs comparisons in deterministic time,
depending only on n (the quantity of bytes compared) is required.
Some operating systems provide such a function (e.g., NetBSD's
consttime_memequal()), but no such function is specified in POSIX.
On Linux, you may need to implement such a function yourself.
bstring(3), strcasecmp(3), strcmp(3), strcoll(3), strncasecmp(3),
strncmp(3), wmemcmp(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2024-07-23 memcmp(3)
Pages that refer to this page: bcmp(3), bstring(3), size_t(3type), strcasecmp(3), strcmp(3), strcoll(3), strxfrm(3), void(3type), wmemcmp(3), signal-safety(7)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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