How can I use function objects in C++ STL?

What are function objects in C++ STL?

Function objects, or functors, are objects that can be called as if they were functions. They are used in STL algorithms.

Can you give me an example of a function object?

Sure! A simple example is a struct that overloads the operator(). For instance:

struct Add {
    int operator()(int a, int b) { return a + b; }
};

You can then use it with STL algorithms.

How do I use this function object with std::sort?

You can use it like this:

std::vector<int> vec = {5, 2, 3};
std::sort(vec.begin(), vec.end(), Add());

This will sort the vector using the Add functor.

Are there any built-in function objects in STL?

Yes, STL provides several built-in function objects like std::plus, std::minus, std::greater, and std::less, which can be used directly.