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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 0000000000..cc65fcbd1f --- /dev/null +++ b/man/man3/memcmp.3 @@ -0,0 +1,84 @@ +.\" 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 2021-03-22 "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> +.PP +.BI "int memcmp(const void *" s1 ", const void *" s2 ", 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. +.PP +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 . +.PP +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). +.ad l +.nh +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.BR memcmp () +T} Thread safety MT-Safe +.TE +.hy +.ad +.sp 1 +.SH STANDARDS +POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. +.SH NOTES +Do not use +.BR memcmp () +to compare security critical data, such as cryptographic secrets, +because the required CPU time depends on the number of equal bytes. +Instead, a function that performs comparisons in constant time 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, it may be necessary to implement such a function oneself. +.SH SEE ALSO +.BR bcmp (3), +.BR bstring (3), +.BR strcasecmp (3), +.BR strcmp (3), +.BR strcoll (3), +.BR strncasecmp (3), +.BR strncmp (3), +.BR wmemcmp (3) |