MEMSET(3)              FreeBSD Library Functions Manual              MEMSET(3)

NAME
     memset - write a byte to byte string

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <string.h>

     void *
     memset(void *dest, int c, size_t len);

     #define __STDC_WANT_LIB_EXT1__ 1

     errno_t
     memset_s(void *dest, rsize_t destsz, int c, rsize_t len);

DESCRIPTION
     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
     length of the dest buffer.  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).

RETURN VALUES
     The memset() function returns its first argument.  The memset_s()
     function returns zero on success, non-zero on error.

SEE ALSO
     bzero(3), explicit_bzero(3), set_constraint_handler_s(3), swab(3),
     wmemset(3)

STANDARDS
     The memset() function conforms to ISO/IEC 9899:1990 ("ISO C90").
     memset_s() conforms to ISO/IEC 9899:2011 ("ISO C11") K.3.7.4.1.

FreeBSD 13.1-RELEASE-p6         August 19, 2018        FreeBSD 13.1-RELEASE-p6