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EXPLICIT_MEMSET(3)         Library Functions Manual         EXPLICIT_MEMSET(3)

NAME
     explicit_memset memset_explicit - guarantee writing a byte to a byte
     string

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <string.h>

     void *
     explicit_memset(void *b, int c, size_t len);

     void *
     memset_explicit(void *b, int c, size_t len);

DESCRIPTION
     The explicit_memset() and memset_explicit() functions write len bytes of
     value c (converted to an unsigned char) to the string b.  They are
     guaranteed not to be optimized away by the compiler even if b is no
     longer used and is about to be freed or go out of scope.

RETURN VALUES
     The explicit_memset() function returns the original value of b.

EXAMPLES
     Create a buffer on the stack for a secret key, use it, and then zero it
     in memory before throwing it away.

           void
           f(void)
           {
                   uint8_t key[32];

                   crypto_random(key, sizeof(key));
                   do_crypto_stuff(key, sizeof(key));
                   ...

                   explicit_memset(key, 0, sizeof(key));
           }

SEE ALSO
     consttime_memequal(3), memset(3)

STANDARDS
     The memset_explicit() function conforms to ISO/IEC 9899:2024 ("ISO C23").

HISTORY
     The explicit_memset() function appeared in NetBSD 7.0.  The
     memset_explicit() alias was added in NetBSD 11.0.

NetBSD 11.99                   November 1, 2024                   NetBSD 11.99