DragonFly On-Line Manual Pages
MEMSET(3) DragonFly Library Functions Manual MEMSET(3)
memset, memset_s - write a byte to byte string
Standard C Library (libc, -lc)
memset(void *dest, int c, size_t len);
memset_s(void *dest, rsize_t destsz, int c, rsize_t len);
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
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).
The memset() function returns its first argument. The memset_s()
function returns zero on success, non-zero on error.
bzero(3), explicit_bzero(3), set_constraint_handler_s(3), swab(3),
The memset() function conforms to ISO/IEC 9899:1990 ("ISO C90").
memset_s() conforms to ISO/IEC 9899:2011 ("ISO C11") K.184.108.40.206.
DragonFly 5.7-DEVELOPMENT September 14, 2019 DragonFly 5.7-DEVELOPMENT