function template partial specialization 'swap' is not allowed

Question

I'm struggling with templates. The following compiles for me just fine:

//foo.h
class foo {
public:
    template <typename T>
    void swap(T* values, uint8_t offset)
    {
        T swp = values[offset];
        values[offset] = values[offset + 1];
        values[offset + 1] = swp;
    }
};

This does not:

//foo.h
class foo {
public:
    template <typename T>
    void swap(T* values, uint8_t offset);
};

//foo.cpp
template <typename T>
void foo::swap<T>(T* values, uint8_t offset)
{
    T swp = values[offset];
    values[offset] = values[offset + 1];
    values[offset + 1] = swp;
}

I get the error message

error: function template partial specialization 'swap<T>' is not allowed

I don't know what that means so I'm unclear on how to proceed. Thanx in advance.

Answer 1

Remove the <T>:

template <typename T>
void foo::swap(T* values, uint8_t offset)
{
    // …
}

That syntax is for template specialization.

Also, you will most likely want your template definitions in the header file, see Why can templates only be implemented in the header file?.