I have a vector of vectors, and I want to connect them one by one to form a long vector. This could be done by inserting at the end. Inspired by this question, I was thinking that using make_move_iterator would replace copy with move and thus would be more efficient. But the following test demonstrates that make_move_iterator will cause a larger time consumption.
#include <iostream>
#include <string>
#include <vector>
#include <chrono>
using namespace std;
int main()
{
string a = "veryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongstring";
vector<string> b(10,a);
vector<vector<string> > c(1000,b);
vector<string> d,e;
auto t1 = chrono::system_clock::now();
for(auto& item : c)
{
d.insert(d.end(),item.begin(),item.end());
}
cout << c[0][0].length() << endl;
auto t2 = chrono::system_clock::now();
for(auto& item:c)
{
e.insert(e.end(), std::make_move_iterator(item.begin()),std::make_move_iterator(item.end()));
}
auto t3 = chrono::system_clock::now();
cout << chrono::duration_cast<chrono::nanoseconds>(t2-t1).count() << endl;
cout << chrono::duration_cast<chrono::nanoseconds>(t3-t2).count() << endl;
cout << c[0][0].length() << endl;
cout << "To check that c has been moved from." <<endl;
}
//Output:
//122
//1212000
//1630000
//0
//To check that c has been moved from.
Thus I'm wondering, does this approach really help improve efficiency?
