我有一个矢量矢量，我想逐个连接它们以形成一个长矢量。这可以通过最后插入来完成。灵感来自this question，我认为使用make_move_iterator会将copy替换为move，从而效率更高。但是以下测试表明make_move_iterator会导致更长的时间消耗。
#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.
因此，我想知道，这种方法真的有助于提高效率吗？