Determine if a string is a valid IPv4 address in C

Question

What would be a good way to determine if a string contains an IPv4 address? Should I use isdigit()?

Answer 1

int validateIP4Dotted(const char *s)
{
    int len = strlen(s);

    if (len < 7 || len > 15)
        return 0;

    char tail[16];
    tail[0] = 0;

    unsigned int d[4];
    int c = sscanf(s, "%3u.%3u.%3u.%3u%s", &d[0], &d[1], &d[2], &d[3], tail);

    if (c != 4 || tail[0])
        return 0;

    for (int i = 0; i < 4; i++)
        if (d[i] > 255)
            return 0;

    return 1;
}