C strings

#include <stdio.h>
#include <string.h>

// This fails if str isn't correctly terminated
int nums1(const char *str, size_t unused) {
    char *a;
    a = (char *)str;
    int num = 0;

    printf("%x: ", a);
    if(!str) return num;
    while(*a) {
        if(*a == ',') num++;
        printf("%x ", a);
        a++;
    }
    printf("\n");

    return num;
}

// This fails if str isn't correctly terminated
int nums2(const char *str, size_t unused) {
    int i;
    int num = 0;
    printf("%x: ", str);
    if(!str) return num;
    for(i = 0; i < strlen(str); i++) {
        printf("%x ", &str[i]);
        if(str[i] == ',') num++;
    }
    printf("\n");

    return num;
}

// likely the safest assuming a correct len is passed in
int nums3(const char *str, size_t len) {
    int i;
    int num = 0;

    printf("%x: ", str);

    if(!str) return num;

    for(i = 0; i < strnlen(str, len); i++) {
        printf("%x ", &str[i]);
        if(str[i] == ',') num++;
    }
    printf("\n");

    return num;
}

#define nums(x, y) nums1(x, y)

int main(int argc, char *argv[]) {
    printf("%d\n", nums("", 0));
    printf("%d\n", nums("5, 10", 6));

    char str1[] = "5, 10";
    printf("%d\n", nums(str1, strlen(str1)));

    char *str2 = "5, 10";
    printf("%d\n", nums(str2, strlen(str2)));

    char str3[9] = "5, 10";
    // Overflow str3 by 1
    int i;
    for(i = 0; i <= 9; i++)
        str3[i] = 0x7F;
    printf("%d\n", nums(str3, 9));

    printf("%d\n", nums(NULL, 0));

    return 0;
}