comparing version numbers in c

Question

I am seeing a lot of answers for this problem in other languages but I am trying to find out a way to compare 2 version numbers given as strings. For example

str1 = "141.1.23"
str2 = "141.1.22"

I am trying to find a way to compare the integer values in the strings to see which one is larger. (In this case str1 would be larger). I thought about using sometime of combination with atoi and strtok but I know I wont be able to tokenize 2 strings at once. Any advice?

Answer 1

I really wonder why people strive for such complicated solutions when there is sscanf in C. Here is a very simple solution to that problem that will work for 99% of all use cases:

int compVersions ( const char * version1, const char * version2 ) {
    unsigned major1 = 0, minor1 = 0, bugfix1 = 0;
    unsigned major2 = 0, minor2 = 0, bugfix2 = 0;
    sscanf(version1, "%u.%u.%u", &major1, &minor1, &bugfix1);
    sscanf(version2, "%u.%u.%u", &major2, &minor2, &bugfix2);
    if (major1 < major2) return -1;
    if (major1 > major2) return 1;
    if (minor1 < minor2) return -1;
    if (minor1 > minor2) return 1;
    if (bugfix1 < bugfix2) return -1;
    if (bugfix1 > bugfix2) return 1;
    return 0;
}

Here, give it a try: https://ideone.com/bxCjsb

Answer 2

I know I wont be able to tokenize 2 strings at once.

Fortunately, you do not need to: make a function that takes a string, and parses it for three integer numbers using strtok_r (use a reentrant version, it's a lot safer).

strunct version_t {
    int major;
    int minor;
    int build;
};

version_t parse_ver(const char* version_str) {
    version_t res;
    // Use strtok_r to split the string, and atoi to convert tokens to ints
    return res;
}

Now you can call parse_ver twice, get two version_t values, and compare them side-by-side.

P.S. If you adopt a convention to always pad the numbers with leading zeros to a specific length, i.e. make sure that you write "141.1.03" and not "141.1.3", you could substitute integer comparison with lexicographic one.