Separate Template Definition I wrote class Data in header. The C++ Compiler compiled without errors. I decided to move all member functions into source code because they are for implementation. I do not like that they are placed in class body.

    I wrote class Data in header. The C++ Compiler compiled without
errors. I decided to move all member functions into source code
because they are for implementation. I do not like that they are
placed in class body.

    I got error message:

Linking...
Main.obj : error LNK2001: unresolved external symbol "public:
__thiscall Data<unsigned char>::operator unsigned char(void)" (??B?
$Data@E@@QAEEXZ)
C:\Main.exe : fatal error LNK1120: 1 unresolved externals

    Could be problem with member function cast operator. All other
member functions complied without any problems.

// Data.h
#if !defined(DATA_H )
#define DATA_H

template< typename T >
class Data {
public:
    Data();
    ~Data();

    operator unsigned char ();

private:
    unsigned char x;
};

#endif // end macro !defined( DATA_H )

// Data.cpp

template< typename T >
Data< T >::Data() : x( 5 ) {}

template
Data< unsigned char >::Data();

template< typename T >
Data< T >::~Data() {}

template
Data< unsigned char >::~Data();

// Error unresolved linkage
template< typename T >
Data< T >::operator unsigned char () {
    return x;
}

template
Data< unsigned char >::operator unsigned char ();

// main.cpp

int main() {
    Data< unsigned char> data;
    unsigned char x = data;

    return 0;
}