c++中vector数据拷贝提速

如果想要在C++程序中用vector传递一个大内存，用swap是比较快的方法，不过传递之后，原始数据就不存在了。

如果后续不再使用原数据，用swap会比较好。

#include <iostream>
#include <ctime>
#include <vector>

using namespace std;

int main()
{
    int length = 10000000;

    vector<double> vecsrc;
    vector<double> vecdst1, vecdst2, vecdst3;
    for (int i = 0; i < length; i++)
    {
        vecsrc.emplace_back(rand());
    }

    clock_t t1 = clock();
    vecdst1 = vecsrc;
    clock_t t2 = clock();
    cout << "t1:" << t2 - t1 << endl <<"size: " << vecsrc.size()<<"  "<< vecdst1.size() << endl;
    
    vecdst2.resize(vecsrc.size());
    copy(vecsrc.begin(), vecsrc.end(), vecdst2.begin());
    clock_t t3 = clock();
    cout << "t2:" << t3 - t2 << endl << "size: " << vecsrc.size()<<"  "<< vecdst2.size() << endl;

    vecsrc.swap(vecdst3);
    clock_t t4 = clock();
    cout << "t3:" << t4 - t3 << endl << "size: " << vecsrc.size()<<"  "<< vecdst3.size() << endl;

    return 0;
}