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Global Object Variable problem...

Started by philkills Oct 11, 2006 at 2:56 PM 6 replies 1k views

Original Post

Oct 11, 2006 at 2:56 PM

Hi all, i have been trying to create a global object so that it can be manipulated by a variety of classes within my program.... Only problem is i keep getting a variety of errors and i have no idea why =/ i have created a file called GlobalVar.h to store the variable..(and any others i choose to in the future) here it is: #ifndef GLOBAL_VAR_H #define GLOBAL_VAR_H #include "TileMapTool.h" // Globals extern TileMapTool* g_pTMData; #endif TileMapTool is a class... but all i get is these errors: error C2143: syntax error : missing ';' before '*' error C2501: 'g_pTMData' : missing storage-class or type specifiers does anyone have any idea why? its quite annoying >_< thx in advance ^_^

ToohrVyk

238

ToohrVyk

Oct 11, 2006 at 3:02 PM

Does "TileMapTool.h" include "GlobalVar.h" ? It shouldn't.

NotAYakk

Oct 11, 2006 at 3:04 PM

Most likely, "TileMapTool.h" is including "GlobalVar.h".

Some .cpp file #includes "TileMapTool.h". It has a header-guard. It then includes "GlobalVar.h", which includes "TileMapTool.h", which is skipped thanks to the header-guard, and the symbol TileMapTool isn't define.

Might I suggest:

#ifndef GLOBAL_VAR_H#define GLOBAL_VAR_H#include "TileMapTool.h"class TileMapTool;// Globalsextern TileMapTool* g_pTMData;#endif

And might I also suggest using namespaces and hiding global variables in accessor functions?

Ie:

#ifndef GLOBAL_VAR_H#define GLOBAL_VAR_H#include "TileMapTool.h"namespace MyProject {  class TileMapTool;  // Globals  TileMapTool* GlobalTileMapTool();}#endif

Fruny

203

Fruny

Oct 11, 2006 at 3:29 PM

class TileMapTool;extern TileMapTool* g_pTMData;

Would be enough. Multiple declarations aren't an error, so long as all the declarations are identical, so there technically isn't a need for header guards in this particular case. Furthermore declaring a pointer to some type doesn't require the type itself to be defined, so you don't need to include TileMapTool.h either.

philkills

Author

philkills

Oct 11, 2006 at 3:37 PM

what i have done is create a file called StdAfx.h with all the includes in it

#ifndef STDAFX_H
#define STDAFX_H

#include
#include
#include
#include
#include
#include
#include
#include
#include "ConstDefinitions.h"
#include "MirMap.h"
#include "TileMapTool.h"

#endif

then in all the header files i simply #include "StdAfx.h"...

i thought that aslong as something has already been loaded... then its fine

update:

Added class TileMapTool;

now i get this error:
MirToSomaSpl.obj : error LNK2001: unresolved external symbol "class TileMapTool * g_pTMData" (?g_pTMData@@3PAVTileMapTool@@A)

lol...

okonomiyaki

Oct 11, 2006 at 4:10 PM

Quote:
Original post by philkills

now i get this error:
MirToSomaSpl.obj : error LNK2001: unresolved external symbol "class TileMapTool * g_pTMData" (?g_pTMData@@3PAVTileMapTool@@A)

You have to actually declare your variables somewhere. All the extern statement is doing is telling everything that this variable is declared, but it has external linkage. Make a GlobalVar.cpp or something that includes just this:

TileMapTool* g_pTMData;

philkills

Author

philkills

Oct 11, 2006 at 4:35 PM

thx alot mate ^_^

Zahlman

257

Zahlman

Oct 11, 2006 at 7:19 PM

Quote:
Original post by philkills
#include
#include
#include
#include

Hold on, do you think you're writing C, or C++?

You do know that std::string lives in rather than , yeah?

Quote:

#include
#include
#include

WTF are *those*? Not the C++ standard, that's for sure. Hint: you've had 8 whole years to get clued in. The standard C++ library now uses header names without a .h extension, and makes use of this lovely feature of the language called "namespaces"; it puts all those symbols into the std:: namespace.

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