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

Tested it for 900k iterations Its taking time 43 seconds for pre-calculated size and 42 seconds for using the size() call.

If you guaranteed vector size doesn't change in the loop, better to use pre-calculated size otherwise there is no choice and must use size().

#include 
#include 

using namespace std;

int main() {
vector v;

for (int i = 0; i < 30000; i++)
        v.push_back(i);

const size_t v_size = v.size();
for(int i = 0; i < v_size; i++)
        for(int j = 0; j < v_size; j++)
                cout << "";

//for(int i = 0; i < v.size(); i++)
//      for(int j = 0; j < v.size(); j++)
//              cout << "";
}