strlcpy实现

#include <stdio.h>

/*
 * Copy src to string dst of size siz.  At most siz-1 characters
 * will be copied.  Always NUL terminates (unless siz == 0).
 * Returns strlen(src); if retval >= siz, truncation occurred.
 */
int strlcpy(char *dst, const char *src, int siz)
{
	register char *d = dst;
	register const char *s = src;
	register size_t n = siz;

	/* Copy as many bytes as will fit */
	if (n != 0 && --n != 0) {
		do {
			if ((*d++ = *s++) == 0)
				break;
		} while (--n != 0);
	}

	/* Not enough room in dst, add NUL and traverse rest of src */
	if (n == 0) {
		if (siz != 0)
			*d = '\0';		/* NUL-terminate dst */
		while (*s++)
			;
	}

	return (s - src - 1);	/* count does not include NUL */
}

int main()
{
    char buf[5];
    char *s[] = {"abc", "abcd", "abcde", "abcdef"};
    int i, len, size = sizeof(buf);

    for (i = 0; i < 5; i++) {
        buf[i] = '#';
    }

    printf("size = %d\n", size);

    for (i = 0; i < 4; i++) {
        len = strlcpy(buf, s[i], size);
        printf("src = %s, len = %d, buf = %s", s[i], len, buf);
        if (size <= len) {
            printf(", truncation occurred\n");
        } else {
            printf("\n");
        }
    }

    return 0;
}