c++ - Would Iterator loop call end() for many times? - 


#include <vector> #include <iostream>  class range {     typedef typename std::vector<int> vec;     typedef typename vec::iterator iterator; public:     range(vec& vec, const int start_id, const int size)             : vec_{vec},               it_begin_{vec_.begin() + start_id},               it_end_  {vec_.begin() + start_id + size}     {}     iterator& begin() {return it_begin_;}     iterator& end()   {return it_end_;} private:     vec& vec_;     iterator it_begin_;     iterator it_end_; };  int main() {     std::vector<int> a;     a.resize(100);     range range(a,0,10);     (auto = range.begin(); != range.end(); ++it) { // line         std::cout << - range.begin() << "\n"; // line b     } }

assembly here

suppose use optimization (like g++ -ofast).

in line a, program call range.end() many times, instead of saving value of range.end() , compare value in every iteration of loop?

in line b, program call range.begin() many times, instead of saving value of range.begin() whole loop , subtract value in every iteration of loop?

in code, optimizer can see implementations of begin() , end(). can inline them, , hoist invariants out of loop.

the answer different if begin() , end() in different translation unit main(), link-time late such optimizations.


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