memset

将内存中的一段空间设定一个值。返回这段内存区的指针。
一般用于对内存的初始化。如：

struct sample *p = malloc(sizeof(struct sample));
memset(p, 0, sizeof(struct sample));

void *memset (void *s, int c, register size_t n)
{
    register unsigned char  val = (unsigned char)  c;
    register unsigned char *ptr = (unsigned char*) s;

    register unsigned char *end = ptr + n;

    while (ptr < end)
        *ptr++ = val;
    return (s);
}