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BZERO(3) Library Functions Manual BZERO(3)

bzero, explicit_bzero
write zeroes to a byte string

#include <strings.h>
bzero(void *b, size_t len);
#include <string.h>
explicit_bzero(void *b, size_t len);

The bzero() function writes len zero bytes to the string b. If len is zero, bzero() does nothing.
The explicit_bzero() variant behaves the same, but will not be removed by a compiler's dead store optimization pass, making it useful for clearing sensitive memory such as a password.

memset(3), swab(3)

The bzero() function first appeared in 4.2BSD. The explicit_bzero() function first appeared in OpenBSD 5.5.
November 24, 2015 OpenBSD-6.1