Initialize a reference to HINSTANCE inside constructor

Question

I've a class and I want to make it as a global object(I have a good reason for it), but for that I need to initialize all the elements(If not I get C2512 No default constructor) which is a problem because I use a reference to an HINSTANCE on it that I need to initialize too and I don't know what can I do that. Here is the code:

class Foo {
private:
    //Class data
    HINSTANCE hInstance;
public:
    Foo(HINSTANCE & hInstance = ??, std::string name = "Default");
};

Foo foo;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    foo = Foo(hInstance, "SomeName");
}

Any Idea of how can I do that?, Thanks!

Answer 1

There is no reason to pass the HINSTANCE by reference if the constructor is not going to modify it, only store it. HINSTANCE is already a pointer to begin with, so just pass it by value and default it to NULL, eg:

class Foo
{
private:
    //Class data
    HINSTANCE hInstance;
public:
    Foo(HINSTANCE hInstance = NULL, const std::string &name = "Default");
};

Foo::Foo(HINSTANCE hInstance, const std::string &name)
    : hInstance(hInstance)
{
    //...
}

Then you can do this:

Foo foo;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    foo = Foo(hInstance, "SomeName");
    //...
}

Alternatively:

#include <memory>

std::unique_ptr<Foo> foo; // or std::auto_ptr before C++11

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    foo.reset(new Foo(hInstance, "SomeName"));

    // or, in C++14 and later...
    // foo = std::make_unique<Foo>(hInstance, "SomeName");

    //...
}