How to declare friend operator<< and operator>> in a class template

Question

It seems like I was unable to declare and implement the insertion (<<) and extraction (>>) operators for a class properly (note that both of them worked fine before I made the class a class template by adding a type template parameter to it).

I have this class template:

template < class Allocator = std::allocator<char> >
class CharMatrix
{
// ...
};

Inside the class in the header file:

template <class Allocator>
friend std::ofstream& operator<<( std::ofstream& ofs, const CharMatrix<Allocator>& char_matrix );

template <class Allocator>
friend std::ifstream& operator>>( std::ifstream& ifs, CharMatrix<Allocator>& char_matrix );

And in the source file:

template <class Allocator>
std::ofstream& operator<<( std::ofstream& ofs, const CharMatrix<Allocator>& char_matrix )
{
// ...
}

template <class Allocator>
std::ifstream& operator>>( std::ifstream& ifs, CharMatrix<Allocator>& char_matrix )
{
// ...
}

I'm getting this error:

CharMatrix.h:99:19: error: declaration of template parameter ‘Allocator’ shadows template parameter
   99 |         template <class Allocator>
      |                   ^~~~~
CharMatrix.h:35:12: note: template parameter ‘Allocator’ declared here
   35 | template < class Allocator = std::allocator<char> >
      |            ^~~~~

What is the proper syntax for this?

How to declare friend operator<< and operator>> in a class template

0 Answers0