c++ 满足条件拷贝，容器扩容（copy_if）

#include <iostream>     // cout
#include <algorithm>    // copy_if, distance
#include <vector>       // vector
using namespace std;
int main () {
    vector<int> foo = {25,15,5,-5,-15};
    vector<int> bar (foo.size());
    
    // copy only positive numbers:
    auto it = copy_if (foo.begin(), foo.end(), bar.begin(), [](int i){return !(i<0);} );
    bar.resize(distance(bar.begin(),it));  // shrink container to new size
    
    cout << "bar contains:";
    for (int& x: bar) cout << ' ' << x;
    cout << '
';
    
    return 0;
}