Question

I’d like to implement search using C generics

int lsearchGeneric(void *key, void *base, int n, int elemSize)
{
    int i =0;

    for(; i < n; i++)   {
        void *elemAddr = (char*) base + i * elemSize;           
        if(memcmp(key, elemAddr , elemSize) == 0) {
            return i;
        }
    }

    return -1;
}

This function is called with

char *key = strdup("w");
char *base = strdup("two");

int result = lsearchGeneric (&key, base, 3, sizeof(char));
printf("Position: %d\n", result); // prints -1

I wonder what am i missing here. Instead of -1, i would expect 1, as “w” is the second letter in “two”

For those (you know who you are) who wonder whether this is homework – the answer is “no it is not. I am following Programming paradigms lecture from iTunesU”

Answer 1

Looks like you have an extra & in your function call:

int result = lsearchGeneric (&key, base, 3, sizeof(char));
                             ^
                        does not belong here!

You’re passing the address of the pointer rather than the pointer itself. The giveaway here is that you weren’t consistent with the two operands: You passed &key and base, one with and the other without the &.

Small Note:

This “generic” might not work properly with structs that have padding. As the padding values are unspecified and may be different with otherwise identical structs.