SFML game dev. Book, chapter 3 textureholder

[danielsega]

I am following the book and i started implementing the aircraft constructor, when i really got confused with the book:

//--Aircraft
Aircraft::Aircraft(Type type, const TextureHolder& textures) : mType(type), mSprite(textures.get(toTextureID(type)))
{
        sf::FloatRect bounds = mSprite.getLocalBounds();
        mSprite.setOrigin(bounds.width / 2.0f, bounds.height / quote);
}

//--ResourceIden
template <typename Resource, typename Identifier>
class ResourceHolder;

typedef ResourceHolder<sf::Texture, Textures::ID>       TextureHolder;
}

How does TextureHolder have access to a get function member, since ResourceHolder is not defined?

[Nexus]

It is defined at the point where it is used: in the header ResourceHolder.hpp.

ResourceIdentifiers.hpp just contains a forward declaration for the typedefs. Typedef doesn't require complete types.

[danielsega]

It is defined at the point where it is used: in the header ResourceHolder.hpp.

ResourceIdentifiers.hpp just contains a forward declaration for the typedefs. Typedef doesn't require complete types.

I get that, but according to the book sample, there is no pre-processor operation that includes ResourceHolder on ResourceIdentifiers. The the aircraft doesn't know about ResourceHolder, it only knows about ResourceIdentifiers, so it does not know about ResourceHolder,  unless if it becomes static. I don't see how they are linked.

[Nexus]

The the aircraft doesn't know about ResourceHolder

Yes, it does. See Aircraft.cpp, line 2.

[dabbertorres]

I think daniel doesn't understand what #include does.

#include basically copies the file to that point.

When you compile, there will essentially be one .cpp file that all your code is in. So, substitute the code in.

Quick example:

Code: [Select]

// Foo.hpp
struct Foo
{
    Foo(int j) {x = j;}
    ~Foo() {}

    int x;
};

// Bar.hpp
struct Foo; // Forward declaration, notice the absence of a #include

struct Bar
{
    Bar(Foo f) {x = f;}
    ~Bar() {}

    Foo x
};

// main.cpp
#include "Bar.hpp" // insert contents of Bar.hpp here
#include "Foo.hpp" // insert contents of Foo.hpp here

int main()
{
    Bar(Foo(5)) baz;
    return 0;
}

Does that make more sense?

[danielsega]

The the aircraft doesn't know about ResourceHolder

Yes, it does. See Aircraft.cpp, line 2.

My bad, i somehow thought that was resourseidentifier.