God forsaken linker errors...

yaya · 12-14-2009, 05:55 PM

I keep getting a damn linker error in this header file. It seams that it works the first time it is processed but every time I call it again, it pops up with another (of the same) error. Here's the code:

Code:

#ifndef MESSAGE_H_
#define MESSAGE_H_

#include "globaltypes.h"

// MESSAGE LIST
enum MSG
{
	MSG_NONE = 0, // default
	MSG_FAIL = 0, //
	MSG_SUCCESS = 1, //
	MSG_OK = 1, //
	
	MSG_ERROR, // string of error message
	MSG_WARNING, // string of warning message

	MSG_TOTALMESSAGETYPES
};

class MESSAGE
{
public:
	MESSAGE();
	~MESSAGE();

	bool Dispatch( MSG Type, void *Data = NULL );
	bool DispatchOne( MSG Type, void *Data, UINT16 Number );
	bool DispatchThis( MSG Type, void *Data = NULL );
	virtual bool Device( const MSG Type, const void *Data );

private:
	UINT16 NumberID;
};

class MESSAGE_TOP
{
public:
	UINT16 Add( MESSAGE* pDevice );
	bool Dispatch( MSG Type, void *Data = NULL );
	bool DispatchOne( MSG Type, void *Data, UINT16 Number );
	MESSAGE* Get( const UINT16 Number ) const;
	UINT16 Remove( const UINT16 Number );
	void RemoveAll();
	UINT16 Size() const;

private:
	std::vector< MESSAGE* > Device;
} extern Message; // THIS IS CAUSING PROBLEMS HERE!!!

#endif

The error is on the line towards the end (extern Message). This is the linker error:

Code:

error LNK2001: unresolved external symbol "class MESSAGE_TOP Message" (?Message@@3VMESSAGE_TOP@@A)

And this is the error without the extern in there:

Code:

error LNK2005: "class MESSAGE_TOP Message" (?Message@@3VMESSAGE_TOP@@A) already defined

I've tried all sorts of things but I give up. This is apart of my global header, so it is known to pretty much every other part of the program.

Thanks.

brewbuck · 12-14-2009, 06:17 PM

Do you actually declare "MESSAGE Message;" in any .cpp file anywhere? An extern on its own is not enough. The extern just tells the rest of the code to expect that symbol to be present at link-time, but doesn't create the symbol.

Also, I'd recommend separating out the extern declaration from the class declaration:

Code:

class MESSAGE
{
    ...
};

extern MESSAGE Message;

yaya · 12-14-2009, 06:26 PM

Yes, that got it... thankyou.

12-14-2009, 06:17 PM	#2
brewbuck Staff software engineer Join Date: Mar 2007 Location: Portland, OR Posts: 6,014	Do you actually declare "MESSAGE Message;" in any .cpp file anywhere? An extern on its own is not enough. The extern just tells the rest of the code to expect that symbol to be present at link-time, but doesn't create the symbol. Also, I'd recommend separating out the extern declaration from the class declaration: Code: class MESSAGE { ... }; extern MESSAGE Message; __________________ "Congratulations on your purchase. To begin using your quantum computer, set the power switch to both off and on simultaneously." -- raftpeople@slashdot
brewbuck is offline

12-14-2009, 06:26 PM	#3
yaya Not stupid, just stupider Join Date: May 2007 Location: Earthland Posts: 191	Yes, that got it... thankyou.
yaya is offline

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