comparing version numbers in c

Question 1

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.

Question 2

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

Question 3

The following routine compares version-number strings that are made up of genuine numbers. The advantage is that the delimiter does not matter; it will work with, for example, 141.01.03, 141:1:3, or even 141A1P3. It also handles mismatched tails so that 141.1.3 will come before 141.1.3.1.

#include <assert.h>
#include <stdlib.h>

int versionCmp( char *pc1, char *pc2)
{
    int result = 0;
    /* loop through each level of the version string */
    while (result == 0) {
        /* extract leading version numbers */
        char* tail1;
        char* tail2;
        unsigned long ver1 = strtoul( pc1, &tail1, 10 );
        unsigned long ver2 = strtoul( pc2, &tail2, 10 );
        /* if numbers differ, then set the result */
        if (ver1 < ver2)
            result = -1;
        else if (ver1 > ver2)
            result = +1;
        else {
            /* if numbers are the same, go to next level */
            pc1 = tail1;
            pc2 = tail2;
            /* if we reach the end of both, then they are identical */
            if (*pc1 == '\0' && *pc2 == '\0')
                break;
            /* if we reach the end of one only, it is the smaller */
            else if (*pc1 == '\0')
                result = -1;
            else if (*pc2 == '\0')
                result = +1;
            /*  not at end ... so far they match so keep going */
            else {
                pc1++;
                pc2++;
            }
        }
    }
    return result;
}

int main( void )
{
    assert(versionCmp("1.2.3" , "1.2.3" ) == 0);
    assert(versionCmp("1.2.3" , "1.2.4" )  < 0);
    assert(versionCmp("1.2.4" , "1.2.3" )  > 0);
    assert(versionCmp("10.2.4", "9.2.3" )  > 0);
    assert(versionCmp("9.2.4",  "10.2.3")  < 0);
    /* Trailing 0 ignored. */
    assert(versionCmp("01", "1") == 0);
    /* Any single space delimiter is OK. */
    assert(versionCmp("1a2", "1b2") == 0);
    return EXIT_SUCCESS;
}

Replace the strtouls with strcspns and a strncmp, and you can use it to compare non-numeric version "numbers" -- but the delimiter must be a dot. For example, 141.3A.1 sorts before 141.3B.

...
while (result == 0) {
    /* ignore leading zeroes */
    pc1 += strspn( pc1, "0" );
    pc2 += strspn( pc2, "0" );
    /* extract leading version strings */
    int len1 = strcspn( pc1, "." );
    int len2 = strcspn( pc2, "." );
    /* if one is shorter than the other, it is the smaller version */
    result = len1 - len2;
    /* if the same length then compare as strings */
    if (result == 0)
        result = strncmp( pc1, pc2, len1 );
    if (result == 0) {
        pc1 += len1;
        pc2 += len2;
        if (*pc1 == '\0' && *pc == '\0')
            ...

Question 4

strverscmp glibc extension

man strverscmp
http://www.gnu.org/software/libc/manual/html_node/String_002fArray-Comparison.html

Example:

#define _GNU_SOURCE
#include <assert.h>
#include <stdlib.h>
#include <string.h>

int main(void) {
    assert(strverscmp("1.2.3" , "1.2.3" ) == 0);
    assert(strverscmp("1.2.3" , "1.2.4" )  < 0);
    assert(strverscmp("1.2.3" , "1.2.2" )  > 0);
    assert(strverscmp("9.2.3" , "10.2.3")  < 0);
    assert(strverscmp("10.2.3", "9.2.3" )  > 0);

    /* Delimiers are also compared. */
    assert(strverscmp("1a2", "1b2" ) < 0);
    assert(strverscmp("1b2", "1a2" ) > 0);

    /* Leading 0s: number gets treated as 0.X, e.g. 01 means 0.1.
     * Maybe not perfect for version strings, but sane version strings
     * should not have leading 0s. 
     */
    assert(strverscmp("01", "9" ) < 0);
    assert(strverscmp("01", "09") < 0);
    assert(strverscmp("01", "09") < 0);
    assert(strverscmp("09",  "1") < 0);

    return EXIT_SUCCESS;
}

Source: https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strverscmp.c;h=96d4227cd50090f3a7c45e7241d817d34e42f5ce;hb=cbc06bc486635347ee0da51d04a82eedf51602d5#l42

Tested on Glibc 2.21, Ubuntu 15.10.

filevercmp from gnulib

Yet another GNU implementation. Source: http://git.savannah.gnu.org/cgit/gnulib.git/tree/libfilevercmp.c?id=71be4c87c8267369f40fbfab7523ab9847154c02#n125

It is used in sort -V of Coreutils 8.23, which works like this: https://stackoverflow.com/a/4024263/895245

Question 5

We can use strtok as suggested. Take a look at this code. To ease it out, im using vector in c++, please use other containers or data structures like array initialized to max of length of the two strings to hold the tokenized elements.

vector<char*> tokenize(char *s)
{
    vector<char*> svec;

    char *stp = strtok(s,".");
    while(stp != NULL)
    {
            svec.push_back(stp);
            stp = strtok(NULL,".");
    }
    cout << endl;
    return svec;

}

int version_compare(char *s1, char *s2)
{
    vector<char*> tokens_s1 = tokenize(s1);
    vector<char*> tokens_s2 = tokenize(s2);

    int st1, st2, flag, maxf,result;
    st1 = tokens_s1.size();
    st2 = tokens_s2.size();
    flag = st1 < st2 ? st1 : st2;


    for(int i=0; i < flag ;i++)
    {

            int one = *(tokens_s1[i]);
            int two = *(tokens_s2[i]);
            if(one > two)
                     return 1;
            else if(one < two)
                    return 2;
            else
                    result = 0;

    }
}

    if((st1 == st2) && (result == 0)) return 0;
    return (st1 > st2 ? 1 : 2);



}


int main()
{
    char s1[] = "1.2.3.4";
    char s2[] = "2.2.3.3.3";
    int st;
    st = version_compare(s1,s2);
    cout<<st<<endl;

}

Question 6

A minimalist C version that only tokenizes the first non-matching component. Uses strchr() and strtoul().

int version_compare(char *s1, char *s2)
{
    char *delim = ".:-";
    while(1) {
        if (*s1 == *s2)  {
            if (!*s1)
                return 0;
            s1++; s2++;
        } else if (strchr(delim, *s1) || !*s1) {
            return -1;
        } else if (strchr(delim, *s2) || !*s2) {
            return 1;
        } else {
            int diff;
            char *end1, *end2;
            diff = strtoul(c1, &end1, 10) - strtoul(c2, &end2, 10);
            if (!diff) {
                c1 += (end1 - c1);
                c2 += (end2 - c2);
            } else {
                return diff;
            }
        }
    }
}