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.Dd November 20, 2024
.Dt MEMCMP 3
.Os
.Sh NAME
.Nm memcmp
.Nd compare bytes in memory
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft int
.Fn memcmp "const void *b1" "const void *b2" "size_t len"
.Sh DESCRIPTION
The
.Fn memcmp
function
compares byte object
.Fa b1
against byte object
.Fa b2 .
Both objects are assumed to be
.Fa len
bytes long.
.Sh RETURN VALUES
The
.Fn memcmp
function returns zero if the two objects are identical.
Zero-length objects are considered identical.
The
.Fn memcmp
function returns a negative value if the first differing byte has a lower
value in
.Fa b1
and a positive value if the first differing byte has a higher value in
.Fa b1 .
.Sh SEE ALSO
.Xr bcmp 3 ,
.Xr strcasecmp 3 ,
.Xr strcmp 3 ,
.Xr strcoll 3 ,
.Xr strxfrm 3 ,
.Xr timingsafe_memcmp 3 ,
.Xr wmemcmp 3
.Sh STANDARDS
The
.Fn memcmp
function
conforms to
.St -isoC .
.Sh CAVEATS
If the objects differ, the C library
.Fn memcmp
implementation returns the difference between the first two differing bytes
.Po treated as
.Vt "unsigned char"
values
.Pc .
This behavior is not specified by
.St -isoC ,
is not portable, and may not occur in light of compiler optimizations.