Compiler not finding my function

Hello All

Strange problem, I just do not understand what is going on... basically, I have a series of template functions and template classes. I am trying to use the template functions within template classes to help me with some of the basic nitty gritty stuff like copying vectors.

I have a template class called state, the real version has many more members, but the one here has a vector<T> member. I am trying to write an assignment operator that can copy the from another state with a different template parameter. This assignment operator calls a template<class T,class U> copyVector function. Yet, when I compile it seems that the compiler cannot find the copyVector function. I don't know what I need to do to get this to bind.

Here is some sample code:

Code:

---

#include <vector>

template<class T,class U>
void copyVector(std::vector<T, std::allocator<T> > &vct, std::vector<U, std::allocator<U> > &asg)
{
        vct.resize(asg.size());
        for(unsigned long i;i<asg.size();i++)
                vct[i]=asg[i];
        return;
}

template<class T>
struct state
{
        std::vector<T> data;

        template<class U> state<T>& operator=(const state<U> &asg)
        {
                copyVector<T,U>(this->data,asg.data);
                return *this;
        }
};

struct cont
{
        double value;
        cont& operator=(const cont &asg)
        {
                this->value=asg.value;
                return *this;
        }
};

int main()
{
        state<double> base;
        state<cont> copy;

        copy=base;
}

---

These are the error messages I get:

Code:

---

test.cpp: In member function ‘state<T>& state<T>::operator=(const state<U>&) [with U = double, T = cont]’:
test.cpp:35:  instantiated from here
test.cpp:20: error: no matching function for call to ‘copyVector(std::vector<cont, std::allocator<cont> >&, const std::vector<double, std::allocator<double> >&)’

---

The compiler is trying to find a match with a const second argument. Making the second argument const allows you to move forward, where you get a new error (specifically you try to copy a double to a cont, but you don't have a operator= that does that).

asg in your assignment operator is const, so asg.data is also (as a consequence) const. The second argument of your copyVector() therefore needs to be const.

Your next problem will be that there is no way of converting a cont to a double, which I assume is self-explanatory.

Uuuuuhhhhhh

Ok light bulb on!!!!

const-correctness

gets me every time

With all the crazy templates every where I though it had something to do with that. Name binding in templates does not always give expected results. Yet that is another post.

Thanks guys, I have every thing working. Even have all the correct const and operator= it all compiles past those errors. On to the next set....