What type of value should it be returned by getters that return size of vector?

Question

What type of value should be returned by getters that return size of vector?

For example I have many getters in my project of the following type and I need the (int) cast to remove the compile warnings:

int getNumberOfBuildings() const { return (int)buildings.size(); }

Answer 1

The C++03 way:

std::vector<Building>::size_type getNumberOfBuildings() const
{ return buildings.size(); }

The C++11 way:

auto getNumberOfBuildings() const -> decltype(buildings.size())
{ return buildings.size(); }

The C++14 way:

auto getNumberOfBuildings() const
{ return buildings.size(); }

Answer 2

You should return a std::size_t. std::size_t is the return type of vector<T>::size() when you use the default allocator. vector<T>::size() returns vector<T>::size_type which is just a typedef for std::size_t when you use the default allocator (which you are most likely using).