The
memset()
function
writes
len
bytes of value
c
(converted to an
unsigned char)
to the string
dest.
Undefined behaviour from
memset(),
resulting from storage overflow, will occur if
len
is greater than the the length of buffer
dest.
The behaviour is also undefined if
dest
is an invalid pointer.
The
memset_s()
function behaves the same as
memset()
except that an error is returned and the currently registered
runtime-constraint handler is called if
dest
is a null pointer,
destsz
or
len
is greater than
RSIZE_MAX,
or
len
is greater than
destsz
(buffer overflow would occur).
The runtime-constraint handler is called first and may not return.
If it does return, an error is returned to the caller.
Like
explicit_bzero(3),
memset_s()
is not removed through Dead Store Elimination (DSE), making it useful for
clearing sensitive data.
In contrast
memset()
function
may be optimized away if the object modified by the function is not accessed
again.
To clear memory that will not subsequently be accessed it is advised to use
memset_s()
instead of
memset().
For instance, a buffer containing a password should be cleared with
memset_s()
before
free(3).
