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Diffstat (limited to 'man/man3/memcmp.3')
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diff --git a/man/man3/memcmp.3 b/man/man3/memcmp.3 new file mode 100644 index 000000000..206ddad72 --- /dev/null +++ b/man/man3/memcmp.3 @@ -0,0 +1,91 @@ +'\" t +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" References consulted: +.\" Linux libc source code +.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) +.\" 386BSD man pages +.\" Modified Sat Jul 24 18:55:27 1993 by Rik Faith (faith@cs.unc.edu) +.TH memcmp 3 (date) "Linux man-pages (unreleased)" +.SH NAME +memcmp \- compare memory areas +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <string.h> +.P +.BI "int memcmp(const void " s1 [. n "], const void " s2 [. n "], size_t " n ); +.fi +.SH DESCRIPTION +The +.BR memcmp () +function compares the first \fIn\fP bytes (each interpreted as +.IR "unsigned char" ) +of the memory areas \fIs1\fP and \fIs2\fP. +.SH RETURN VALUE +The +.BR memcmp () +function returns an integer less than, equal to, or +greater than zero if the first \fIn\fP bytes of \fIs1\fP is found, +respectively, to be less than, to match, or be greater than the first +\fIn\fP bytes of \fIs2\fP. +.P +For a nonzero return value, the sign is determined by the sign of +the difference between the first pair of bytes (interpreted as +.IR "unsigned char" ) +that differ in +.I s1 +and +.IR s2 . +.P +If +.I n +is zero, the return value is zero. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR memcmp () +T} Thread safety MT-Safe +.TE +.SH STANDARDS +C11, POSIX.1-2008. +.SH HISTORY +POSIX.1-2001, C89, SVr4, 4.3BSD. +.SH CAVEATS +Do not use +.BR 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 +.I n +(the quantity of bytes compared) +is required. +Some operating systems provide such a function (e.g., NetBSD's +.BR consttime_memequal ()), +but no such function is specified in POSIX. +On Linux, you may need to implement such a function yourself. +.SH SEE ALSO +.BR bstring (3), +.BR strcasecmp (3), +.BR strcmp (3), +.BR strcoll (3), +.BR strncasecmp (3), +.BR strncmp (3), +.BR wmemcmp (3) |