CODEWITHSUNDEEP
cpointersmalloc
Jackson
Jackson

Reputation: 13

Having trouble comparing two strings in C

I am trying to take in two strings via command line arguments in C and then compare them. I know that malloc returns a void pointer although I do not understand how to pass this to my compare function because it is looking for a const void pointer. I assume I will have to cast the pointers that point to the memory on the heap where the strings will be allocated (?) although I'm not sure how to go about this, any help is appreciated.

int cmpstringp(const void *arg1, const void *arg2);

int main(int argc, char **argv) {
    char *strOne;
    char *strTwo;
    int n = 10;
    strOne = (char *)malloc((n + 1) * sizeof(char));
    strTwo = (char *)malloc((n + 1) * sizeof(char));
    strOne = argv[1];
    strTwo - argv[2];
    cmpstringp(strOne, strTwo);
}

int cmpstringp(const void *arg1, const void *arg2) {
    const char * const * ptr1 = (const char **)arg1;
    const char * const * ptr2 = (const char **)arg2;

    const char *str1 = *ptr1; 
    const char *str2 = *ptr2;

    return strcmp(str1, str2);
}

Upvotes: 1

Views: 161

Answers (1)

Saucy Goat
Saucy Goat

Reputation: 1675

Just take a look at the return value of applying strcmp directly to argv:

int main(int argc, char * argv[])
{
    int ret;

    ret = strcmp(argv[1], argv[2]);
    if (ret == 0)
        printf("Equal strings.\n");

    return 0;
}

By the way, if you're looking to have a function with generic arguments that compares two strings (i.e. to use in qsort()), here's how you could go about it:

int string_cmp(const void * a, const void * b)
{
     return strcmp((const char*)a, (const char*)b);
}

Upvotes: 5

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