Question

I want to create one so that I could check whether a certain word is in the set using set::find

However, C-strings are pointers, so the set would compare them by the pointer values by default. To function correctly, it would have to dereference them and compare the strings.

I could just pass the constructor a pointer to the strcmp() function as a comparator, but this is not exactly how I want it to work. The word I might want to check could be part of a longer string, and I don’t want to create a new string due to performance concerns. If there weren’t for the set, I would use strncmp(a1, a2, 3) to check the first 3 letters. In fact, 3 is probably the longest it could go, so I’m fine with having the third argument constant.

Is there a way to construct a set that would compare its elements by calling strncmp()? Code samples would be greatly appreciated.

Here’s pseudocode for what I want to do:

bool WordInSet (string, set, length)
{
   for (each word in set)
    {
       if strncmp(string, word, length) == 0
            return true;
    }
    return false;
}

But I’d prefer to implement it using the standard library functions.

Answer 1

Make a wrapper function:

bool myCompare(const char * lhs, const char * rhs)
{
    return strncmp(lhs, rhs, 3) < 0;
}