Differential D47286 Diff 146474 lib/libc/string/memset.3

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lib/libc/string/memset.3

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	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL			.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS			.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)			.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT			.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY			.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF			.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	.\" SUCH DAMAGE.			.\" SUCH DAMAGE.
	.\"			.\"
	.Dd August 19, 2018			.Dd October 24, 2024
	.Dt MEMSET 3			.Dt MEMSET 3
	.Os			.Os
	.Sh NAME			.Sh NAME
	.Nm memset			.Nm memset
	.Nd write a byte to byte string			.Nd write a byte to byte string
	.Sh LIBRARY			.Sh LIBRARY
	.Lb libc			.Lb libc
	.Sh SYNOPSIS			.Sh SYNOPSIS
	.In string.h			.In string.h
	.Ft void *			.Ft void *
	.Fn memset "void *dest" "int c" "size_t len"			.Fn memset "void *dest" "int c" "size_t len"
				.Ft void *
				.Fn memset_explicit "void *dest" "int c" "size_t len"
	.Fd #define __STDC_WANT_LIB_EXT1__ 1			.Fd #define __STDC_WANT_LIB_EXT1__ 1
	.Ft errno_t			.Ft errno_t
	.Fn memset_s "void *dest" "rsize_t destsz" "int c" "rsize_t len"			.Fn memset_s "void *dest" "rsize_t destsz" "int c" "rsize_t len"
	.Sh DESCRIPTION			.Sh DESCRIPTION
	The			The
	.Fn memset			.Fn memset
	function			function
	writes			writes
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	is greater than the length of the			is greater than the length of the
	.Fa dest			.Fa dest
	buffer.			buffer.
	The behaviour is also undefined if			The behaviour is also undefined if
	.Fa dest			.Fa dest
	is an invalid pointer.			is an invalid pointer.
	.Pp			.Pp
	The			The
				.Fn memset_explicit
				function behaves the same as
				.Fn memset, but will not be removed by a compiler's dead store
				optimization pass, making it useful for clearing sensitive memory
				such as a password.
				.Pp
				The
	.Fn memset_s			.Fn memset_s
	function behaves the same as			function behaves the same as
	.Fn memset			.Fn memset
	except that an error is returned and the currently registered			except that an error is returned and the currently registered
	runtime-constraint handler is called if			runtime-constraint handler is called if
	.Fa dest			.Fa dest
	is a null pointer,			is a null pointer,
	.Fa destsz			.Fa destsz
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	.Fn memset .			.Fn memset .
	For instance, a buffer containing a password should be cleared with			For instance, a buffer containing a password should be cleared with
	.Fn memset_s			.Fn memset_s
	before			before
	.Xr free 3 .			.Xr free 3 .
	.Sh RETURN VALUES			.Sh RETURN VALUES
	The			The
	.Fn memset			.Fn memset
	function returns its first argument.			and
				.Fn memset_explicit
				functions return their first argument.
	The			The
	.Fn memset_s			.Fn memset_s
	function returns zero on success, non-zero on error.			function returns zero on success, non-zero on error.
	.Sh SEE ALSO			.Sh SEE ALSO
	.Xr bzero 3 ,			.Xr bzero 3 ,
	.Xr explicit_bzero 3 ,			.Xr explicit_bzero 3 ,
	.Xr set_constraint_handler_s 3 ,			.Xr set_constraint_handler_s 3 ,
	.Xr swab 3 ,			.Xr swab 3 ,
	.Xr wmemset 3			.Xr wmemset 3
	.Sh STANDARDS			.Sh STANDARDS
	The			The
	.Fn memset			.Fn memset
	function			function
	conforms to			conforms to
	.St -isoC .			.St -isoC .
	.Fn memset_s			.Fn memset_s
	conforms to			conforms to
	.St -isoC-2011			.St -isoC-2011
	K.3.7.4.1.			K.3.7.4.1.
				.Fn memset_explicit
				conforms to
				.St -isoC-2024 .