Question

I develope a library, when I compile my code with GCC (in Windows with CodeBlocks), The source code doesn’t compile and this error appears:

error: incomplete type ‘claculator’ used in nested name specifier.

I write a sample code that generate this error exactly:

class claculator;

template<class T>
class my_class
{
    public:

    void test()
    {
        // GCC error: incomplete type 'claculator' used in nested name specifier
        int x = claculator::add(1, 2);
    }

    T m_t;
};

// This class SHOULD after my_class.
// I can not move this class to top of my_class.
class claculator
{
    public:

    static int add(int a, int b)
    {
        return a+b;
    }
};

int main()
{
    my_class<int> c;
    c.test();

    return 0;
}

How can I solve this error?

Note that my source code compiled successfully in Visual Studio.

Thanks.

Answer 1

Its very simple. Define test() after the definition of calculator class as:

class calculator;

template<class T>
class my_class
{
    public:

    void test(); //Define it after the definition of `calculator`

    T m_t;
};

// This class SHOULD after my_class.
// I can not move this class to top of my_class.
class calculator
{
    public:

    static int add(int a, int b)
    {
        return a+b;
    }
};

//Define it here!
template<class T>
void my_class<T>::test()
{
     int x = calculator::add(1, 2);
}

In this way, the complete definition of calculator is known to the compiler when it parses the definition of test().