Question

How can i use std::swap to copy a vector to a vector in an struct? Heres an example of what i’m tying to do

#include<vector>

using namespace std;

struct test{
    vector<int> a;
    vector<int> b;
};

int main(){

    int data[] = { 1, 2, 3 };
    int data2[] = {3,4,5 };
std::vector<int> c( &data[0], &data[0]+sizeof(data)/sizeof(data[0]));
std::vector<int> d( &data2[0], &data2[0]+sizeof(data2)/sizeof(data2[0]));


    test A = test(swap(c) , swap(d) );



}

Answer 1

You can’t swap into a constructor or function argument. You can only swap into an lvalue. This is one of the reasons why C++11 introduced move semantics to begin with: to allow the user to explicitly move objects into parameters and so forth.

So you would need to give test an appropriate constructor and call it, using std::move to convert your lvalue vector objects into rvalue references.

struct test{
    test(vector<int> _a, vector<int> _b) : a(std::move(_a)), b(std::move(_b)) {}
    vector<int> a;
    vector<int> b;
};

...

test A{std::move(c), std::move(d)};

If you really want to copy the vectors, you would do this instead:

test A{c, d};