用C语言实现ipv4地址字符串是否合法

用程序实现ipv4地址字符串是否合法，主要考察的是C字符串的操作。

搜索了下，网上没有特别好的实现，自己实现了下，见笑于大家，请指正。

#include <stdio.h>
#include <string.h>
int valid_ip_segment(const char* begin,
                     const char* end) {
    int len = end - begin;
    if (len <  || len > ) {
        return -; // unvalid_length
    }
    int sum = ;
    while (begin < end) {
        if (!isdigit(*begin)) {
            return -; // unvlaid_char
        }
        sum *= ;
        sum += *begin - '';
        ++begin;
    }
    if (sum > ) {
        return -;// unvalid_sum
    }
    return ;
}

int valid_ip_address(const char* ip_str) {
    if (!ip_str) {
        return -;
    }
    const char* begin = ip_str;
    const char* end = NULL;
    int seg_count = ;
    int ret = ;
    while ((end = strchr(begin, '.'))) {
        if ((ret = valid_ip_segment(begin, end)) < ) {
            return ret;
        }
        ++seg_count;
        begin = end + ;
    }
    if (seg_count != ) {
        return -;
    }
    end = begin;
    while(*end) {
        ++end;
    }
    return valid_ip_segment(begin, end);
}

struct TestCase {
    const char* ip_address;
    int expect_ret;
};

int main() {
    const struct TestCase test_case[] = {
        {"102.1.1.x1", -},
        {"102.1.11.11", },
        {"102.1.881.1", -},
        {"102.1.8.-1", -},
        {"102.1.8..1", -},
        {"102.1.1.-x3xx", -}
    };
    size_t len = sizeof(test_case)/sizeof(test_case[]);
    int i = ;
    int ret = ;
    for (;i < len; ++i ) {
        if ((ret = valid_ip_address(test_case[i].ip_address))
             != test_case[i].expect_ret) {
            printf("expect %d\t but return %d\n", test_case[i].expect_ret , ret);
        } else {
            printf("%s\t is with ret %d\n", test_case[i].ip_address, ret);
        }
    }
    return ;
}