compare function for upper_bound / lower_bound

Question

I want to find the first item in a sorted vector that has a field less than some value x.
I need to supply a compare function that compares \'x\' with the internal value

Answer 1

What function did you pass to the sort algorithm? You should be able to use the same one for upper_bound and lower_bound.

The easiest way to make the comparison work is to create a dummy object with the key field set to your search value. Then the comparison will always be between like objects.

Edit: If for some reason you can't obtain a dummy object with the proper comparison value, then you can create a comparison functor. The functor can provide three overloads for operator() :

struct MyClassLessThan
{
    bool operator() (const MyClass & left, const MyClass & right)
    {
        return left.key < right.key;
    }
    bool operator() (const MyClass & left, float right)
    {
        return left.key < right;
    }
    bool operator() (float left, const MyClass & right)
    {
        return left < right.key;
    }
};

As you can see, that's the long way to go about it.