global variables

da_cobra · 2001-12-14T09:00:07

there is a thing that I still don't quite understand and so I keep on getting these kind of errors : say I have a boolean in my windows message loop to know where I am : in the menu, in the game, like this : while (true) { if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message==WM_QUIT) // Have We Received A Quit Message? { // If So break break; } else { TranslateMessage(&msg) ; DispatchMessage(&msg) ; } // end of else } // end of if else { MyGame.CLS() ; // clear the screen if (bMenu=true) Menu() ; // go to the menu function if (bGame=true) GameMain() ; // go to the game loop } } // end of while return 0 ; } // end of WinMain BUT I have to use these booleans in my menu() function so menu option one makes bMenu to true, Menu option 2 => bGame=true so now I put these booleans into my "Globals.h" and include this file in my Winmain.cpp and in my menu.cpp and I also use the "globals.h" in another file clock.cpp but not for these booleans but for other global variables and/or pointers.... so now I get the following error => inMain.obj : error LNK2005: "bool bExit" (?bExit@@3_NA) already defined in Clock.obj WinMain.obj : error LNK2005: "bool bCredits" (?bCredits@@3_NA) already defined in Clock.obj WinMain.obj : error LNK2005: "bool bGame" (?bGame@@3_NA) already defined in Clock.obj WinMain.obj : error LNK2005: "bool bMenu" (?bMenu@@3_NA) already defined in Clock.obj menu.obj : error LNK2005: "bool bExit" (?bExit@@3_NA) already defined in Clock.obj menu.obj : error LNK2005: "bool bCredits" (?bCredits@@3_NA) already defined in Clock.obj menu.obj : error LNK2005: "bool bGame" (?bGame@@3_NA) already defined in Clock.obj menu.obj : error LNK2005: "bool bMenu" (?bMenu@@3_NA) already defined in Clock.obj I know that this error is because I define these booleans over and over, right? How can I avoid this? thanx in advance... Edited by - da_cobra on December 11, 2001 3:14:39 PM Edited by - da_cobra on December 11, 2001 3:15:44 PM

For Beginners

Started by da_cobra December 11, 2001 02:13 PM

12 comments, last by da_cobra 22 years, 4 months ago

Oluseyi

2,123

December 12, 2001 06:58 PM

quote:Header files ...get copied into every cpp file that includes them.

Not exactly or necessarily. It''s pretty close though. A header file should be parsed only once; at compile time all declarations become global, allowing for resolution of all references. This is why we use inclusion guards (#ifndef MY_HEADER_H...) or platform-specific instructions (#pragma once).

Which is more information than most people want or need.

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Thanks to Kylotan for the idea!

CaptainJester

523

December 14, 2001 08:21 AM

If you use those inclusion guards, you do not have to declare the variables as extern.

---
Make it work.
Make it right.
Make it fast.

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Askadar

122

December 14, 2001 08:53 AM

If you define a variable in a cpp file, use extern in other files to tell the compiler that it exists.

If you define a variable in a header file, make it include safe using this pattern:

#ifndef HEADERFILENAME_DEFINED
#define HEADERFILENAME_DEFINED

//here goes the usual header stuff

#endif

This way it will be included only once when compiling the whole project.

Kill mages first!

BaShildy

122

December 14, 2001 09:00 AM

Don''t think anyone else posted about this.
if (bMenu=true) Menu() ; // go to the menu function
if (bGame=true) GameMain() ; // go to the game loop

should be:
if (bMenu==true) Menu() ; // go to the menu function
if (bGame==true) GameMain() ; // go to the game loop

or to prevent these problems from compiling:
if (bMenu) Menu() ; // go to the menu function
if (bGame) GameMain() ; // go to the game loop

or :
if (true == bMenu) Menu() ; // go to the menu function
if (true == bGame) GameMain() ; // go to the game loop

if you don''t understand this, you need to read more about how operators work in C/C++. There a lot more complex then what they look at times.

Code comment of the week:
bool hack = false; // DO NOT CHANGE THIS EVER

- Kevin "BaShildy" KingGame Programmer: DigiPenwww.mpogd.com

global variables

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