Generic Programming in C

[nammae]

Now I am learning Generic Programming in C.

My homework is writing two function:
- Generic copy function (whose functionality is same as memcpy())
- Generic compare function (which can compare two data of any type such as int, float, double, ... ) (not using template or something which is not exist in C)

Here is my first fuction:

void* myMemcpy (void* Destination, const void* Source, int num)
{
	char* first = (char*)Source;
	char* last = (char*)Source + num;
	char* result = (char*)Destination;
	while (first != last)
		*result++ = *first++;
		
	return Destination;
}

But I get a problem with second function. Can you give me some advices?
Thanks for your help.

[Seraphimsan]

post the code for your second function, as well as the problem your having with it.

[mackabee]

Can we see what you have done?

[Duthomhas]

The second function should look very much like the first, except for line 7, which should compare the two values instead of copy one to the other. If the comparision is 'not equal' then your function should terminate with the appropriate 'not equal' code. Otherwise it will eventually find its way to line 9, where it should terminate with the 'equal' code (which in the case of memcmp() is zero).

By the way, you are casting away the constness of your Source, which is a Bad Thing. Don't do that. Finally, take care that your users don't give you a negative num.

void* myMemcpy (void* Destination, const void* Source, int num)
{
	const char* first = (const char*)Source;	// Stays const!
	const char* last = first + num;			// Stays const!
	char* result = (char*)Destination;
	while (first < last)			// No negative num allowed!
		*result++ = *first++;

	return Destination;
}

Hope this helps.

[edit] BTW, your professor should not be calling this "Generic Programming". It is not.

[guestgulkan]

A comparison function for equality only would be straight forward - but I can see less-than and greater-than
test being very messy.

[moorecm]

Unless I'm reading into the question a bit too far, it almost sounds as if the second one should take variable arguments and then compare the memory they occupy.

EDIT: Ah, nevermind, void* would handle the variable argument part.

[nammae]

@everyone: thank you very much.
Here is my function after consulting your ideas:

int GenericCompare (const void* ptr1, const void* ptr2, int num)
{
    const char* first = (const char*)ptr2;
    const char* last = (const char*)ptr2 + num;
    const char* result = (const char*)ptr1;
    while (first < last)
        if (result != first)
            return 0;               // not equal
        else
        {
            ++first;
            ++result;
        }
    return 1;                       // equal
}