STL: how to overload operator= for <vector> ?

Question

There's simple example:

#include <vector>

int main() {
 vector<int> veci;
 vector<double> vecd;

 for(int i = 0;i<10;++i){
  veci.push_back(i);
  vecd.push_back(i);
 }
 vecd = veci; // <- THE PROBLEM
}

The thing I need to know is how to overload operator = so that I could make assignment like this:

vector<double> = vector<int>;

I've just tried a lot of ways, but always compiler has been returning errors...

Is there any option to make this code work without changing it? I can write some additional lines, but can't edit or delete the existing ones. Ty.

Answer 1

You can't. The assignment operator must be a member function, which means it must be a member of the std::vector template which you are not allowed to modify (or so the C++ Standard says). So instead, write a free function:

void Assign( vector <double> & vd, const vector <int> & vi ) {
  // your stuff here
}

Answer 2

Why not do it in a easier way:

vector<double> vecd( veci.begin(), veci.end() );

Or:

vecd.assign( veci.begin(), veci.end() );

Both are supported out of the box :)

Answer 3

OK, I see. I'll ask You in another way.. Is there any option to make this code work without changing it? I can write some additional lines, but can't edit or delete the existing ones. Ty.

Answer 4

If it's a puzzle, this will work...

#include <vector>

int main() 
{
    vector<int> veci;

    {
        vector<double> vecd;
    }

    vector<int> vecd;

    for (int i = 0; i < 10; ++i)
    {
        veci.push_back(i);
        vecd.push_back(i);
    }

    vecd = veci; // voila! ;)
}