C++ Template problem adding two data types

Question

I have a template class with an overloaded + operator. This is working fine when I am adding two ints or two doubles. How do I get it to add and int and a double and return th

Answer 1

Newer answer to an old question. For C++0x you can go with decltype as other answers have talked about. I would argue that common_type is more made for the situation than decltype.

Here is an example of common_type used in a generic add:

#include 
#include 
#include 

using namespace std;

template 
 array::type, N> // <- Gets the arithmetic promotion
 add_arrays(array u, array v)
{
    array::type, N> result; // <- Used again here
    for (unsigned long i = 0; i != N; ++i)
    {
        result[i] = u[i] + v[i];
    }
    return result;
}

int main()
{
    auto result = add_arrays( array {1, 2, 3, 4},
                              array {1.0, 4.23, 8.99, 55.31} );

    for (size_t i = 0; i != 4; ++i)
    {
        cout << result[i] << endl;
    }

    return 0;
}

it basically returns the value that different arithmetic operations would promote to. One nice thing about it is that it can take any number of template args. Note: don't forget to add the ::type at the end of it. That is what gets the actual type result that you want.

For those working pre-c++11 still, there is a boost version of common_type as well