Performance issue for vector::size() in a loop in C++

Question

In the following code:

std::vector var;
for (int i = 0; i < var.size(); i++);

Is the

Answer 1

The size() member function is called each time, but it would be a really bad implementation that wouldn't inline it, and a strange one where it wouldn't be a simple access of a fixed datum or a subtraction of two pointers.
Anyway, you shouldn't worry yourself with such trivialities until you have profiled your application and found out that this is a bottleneck.

However, what you should pay attention to is:

1. The correct type for a vector's index is std::vector::size_type.
2. There are types (some iterators, for example) where i++ might be slower than ++i.

Therefore, the loop should be:

for(vector::size_type i=0; i