speed reference vs by value

i have following question. I tried assignment by value and by reference and as stated here assignment ba value should be faster although when I tried my code it gave me a rather mixed results, as sometimes assign1 is faster, sometimes assign2. ``` class MyAddress{ char *name; long int number; char *street; char *town; char state[2]; long zip; std::vector<int> v_int; public: MyAddress(int i){ v_int.resize(1000000); std::fill(v_int.begin(),v_int.end(),i); } MyAddress& assign1(MyAddress const& x) { MyAddress tmp(x); // copy construction of tmp does the hard work std::swap(*this, tmp); // trade our resources for tmp's return *this; // our (old) resources get destroyed with tmp } MyAddress& assign2(MyAddress x)//x is a copy of the source; hard work already done { std::swap(*this, x); // trade our resources for x's return *this; // our (old) resources get destroyed with x } }; ``` main: ``` for(int i=0;i<10;i++){ { MyAddress a1(1); MyAddress a2(2); MyAddress a3(3); clock_t tstart=std::clock(); a1.assign1(a2); a1.assign1(a3); clock_t tend=std::clock(); float time_elapsed=((float)tend-(float)tstart); std::cout<<std::fixed<<"\nassign1 time elapsed : "<<time_elapsed/CLOCKS_PER_SEC; } { MyAddress a1(1); MyAddress a2(2); MyAddress a3(3); clock_t tstart=std::clock(); a1.assign2(a2); a1.assign2(a3); clock_t tend=std::clock(); float time_elapsed=((float)tend-(float)tstart); std::cout<<"\nassign2 time elapsed : "<<time_elapsed/CLOCKS_PER_SEC; } std::cout<<std::endl; } ``` assign1 time elapsed : 0.093000 assign2 time elapsed : 0.094000 assign1 time elapsed : 0.095000 assign2 time elapsed : 0.092000 assign1 time elapsed : 0.109000 assign2 time elapsed : 0.093000 assign1 time elapsed : 0.099000 assign2 time elapsed : 0.094000 assign1 time elapsed : 0.099000 assign2 time elapsed : 0.101000 assign1 time elapsed : 0.096000 assign2 time elapsed : 0.120000 assign1 time elapsed : 0.098000 assign2 time elapsed : 0.105000 assign1 time elapsed : 0.113000 assign2 time elapsed : 0.108000 assign1 time elapsed : 0.111000 assign2 time elapsed : 0.103000 assign1 time elapsed : 0.106000 assign2 time elapsed : 0.106000 I made some changes to the testing code: now I perform 1000 iterations instead of 10. the results are still mixed: what is specially strange for me is that sometimes first assign is faster but sometimes second: ``` 1) assign1 time elapsed : 111.228996 assign2 time elapsed : 112.097000 2) assign1 time elapsed : 127.087997 assign2 time elapsed : 126.691002 ``` how do you explain this? for me it looks like the result is independent of the value or reference method in this case. finally I have used something like this as I think this is the method suggested here if I understand it correct ``` MyAddress get_names(MyAddress& ref){return ref;} ``` and now in assign2 it is done this way: ``` a1.assign2(get_names(a2)); a1.assign2(get_names(a3)); ``` in fact the performance is slightly better with assign2, at least each time, not interchangeably as before. but is this the difference that I was supposed to see? ``` assign1 time elapsed : 127.087997 assign2 time elapsed : 126.691002 assign1 time elapsed : 137.634995 assign2 time elapsed : 136.054993 ``` finally: ``` assign1 time elapsed : 1404.224976 assign2 time elapsed : 1395.886963 ```