Question

I have the following compare function that I pass to the std::sort algorithm to sort a vector of objects:

template <typename PointT>
bool myCompareLines (A<PointT>::model_struct model_a, A<PointT>::model_struct model_b) {
    return (/* some comparison code*/);
}

The compare function is declared outside the class and I am calling it like this:

template <typename PointT>
class B {
    [...]
    std::sort(lines.begin().lines.end(),::myCompareLines);
    [...]
}

When I compile I get the error: template declaration of 'bool myCompareLines'

Inside class A I declare class B as a friend class so that class B can
access the the private type model_struct. What am I missing?

Answer 1

I was missing the typename keyword in my CompareLines signature.

This fixes it:

bool myCompareLines (typename A<PointT>::model_struct model_a, typename B<PointT>::model_struct model_b)