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.\" Copyright (c) 2012 The NetBSD Foundation, Inc.
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.\" by Alan Barrett
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.Dd February 21, 2012
.Dt MEMSET_S 3
.Os
.Sh NAME
.Nm memset_s
.Nd copy a value to all bytes of a memory buffer
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd "#define __STDC_WANT_LIB_EXT1__ 1
.In string.h
.Ft errno_t
.Fn memset_s "void *s" "rsize_t smax" "int c" "rsize_t n"
.Sh DESCRIPTION
The
.Fn memset_s
function copies the value
.Fa c
(converted to an unsigned char)
into each of the first
.Fa n
bytes of the memory buffer whose starting address is given by
.Fa s .
.Pp
It is a runtime-constraints violation if
.Fa s
is a null pointer,
or if either of
.Fa smax
or
.Fa n
is larger than
.Dv RSIZE_MAX ,
or if
.Fa smax
is smaller than
.Fa n .
If there is a runtime-constraints violation, and if
.Fa s
is not a null pointer,
and if
.Fa smax
is not larger than
.Dv RSIZE_MAX ,
then, before reporting the runtime-constraints violation,
.Fn memset_s
copies
.Fa smax
bytes to the destination.
.Pp
In contrast to the
.Xr memset 3
function,
calls to
.Fn memset_s
will never be
.Dq optimised away
by a compiler.
This property is required by the following sentences in
section K.3.7.4.1 of
.St -isoC-2011 :
.Bd -filled -offset indent
Unlike
.Fn memset ,
any call to the
.Fn memset_s
function shall be evaluated strictly according to the rules of
the abstract machine as described in (5.1.2.3).
That is, any call to the
.Fn memset_s
function shall assume that the memory indicated by
.Fa s
and
.Fa n
may be accessible in the future and thus must contain
the values indicated by
.Fa c .
.Ed
.Sh RETURN VALUES
The
.Fn memset_s
function returns zero for success, or a non-zero error code
if there was a runtime-constraints violation.
.Sh ERRORS
.Fn memset_s
returns the following error codes.
It does not store the error code in the global
.Va errno
variable:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa s
argument was a null pointer.
.It Bq Er E2BIG
One or both of
.Fa smax
or
.Fa n
was larger than
.Dv RSIZE_MAX .
.It Bq Er EOVERFLOW
.Fa n
was larger than
.Fa smax .
.El
.
.Sh SEE ALSO
.Xr memset 3 .
.Sh STANDARDS
The
.Fn memset_s
function conforms to
.St -isoC-2011 ,
except that the
.Fn set_constraint_handler_s
interface is not supported.