CODEWITHSUNDEEP
c++
user3541787
user3541787

Reputation: 53

C++ Correct way to use headers

I'm by no means new to using headers in programs, but I've recently run into a strange problem.

#ifndef PLAYER_HEADER_GUARDS
#define PLAYER_HEADER_GUARDS

#include "CollidableObject.h"
#include "Includes.h"

extern const int ANIMATION_EXTENDER;
extern class MapSystem *mapSystem;

class Player : public CollidableObject
{
     //declaration of rest of the class
};

#endif

I have a lot of classes split across several files (and their respective headers), but here is my current problem : even though I have already included CollidableObject.h, the compiler (CodeBlocks) throws an error

Player.h|12|error: expected class-name before '{' token|

The problem arises from the " : public CollidableObject" part of the code, since the program worked fine before I added that. Shouldn't including the CollidableObject header (I'm not posting it, but it basically looks just the same, and defines the class CollidableObject) remove this kind of a problem? Further,

extern class MapSystem *mapSystem;

This statement should, to the best of my knowledge, compile fine without the extra "class" after extern, but if I remove the class keyword, it throws an error "expected type qualifier before * token". The class MapSystem has also been defined previously, and it should work fine - but without the class keyword, it doesn't.

So that brings me to my question - what mistake am I making in my header files, that is leading to such problems? No multi-filed project that I worked on before had such problems.

Upvotes: 2

Views: 122

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254431

It sounds like either "CollidableObject.h" or "Includes.h" tries to reinclude "Player.h", resulting in a circular dependency. The result is that Player ends up being defined before CollidableObject, so the latter name is not declared at that point.

Make sure neither of these headers, nor any of their dependencies, include "Player.h". You might need to add forward declarations of class Player; if anything needs to use that name.

Also check that "CollidableObject.h" does actually define class CollidableObject (perhaps there's a spelling mistake?), and has a uniquely named include guard.

As for the second question:

extern class MapSystem *mapSystem;

This doubles up as a declaration of class MapSystem, so doesn't require a previous declaration.

extern MapSystem *mapSystem;

This does not declare MapSystem (it only indicates that it's a type name, not a class), so it does require a previous declaration.

Upvotes: 5

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