CODEWITHSUNDEEP
c++
Asen
Asen

Reputation: 62

Global variable in c++ error LNK2020

I have a C++ aplication with one form (Form1.h) and a plugin.ccp file that is the actual application .The program is a plugin for Mach3 cnc controler which comunicates with the cnc machine by USB.

I want a global variable that can be used in Form1.h and in plugin.ccp. A tried with a solution i found on this site.

Form1.h :

extern BOOL B1;

Form1.ccp

#include "Form1.h"
BOOL B1 = TRUE ;

plugin.ccp 

#include "Form1.h"

And it compiles without errors . But when a type something like this

Form1.h

B1 = FALSE;
// or 
SomeOtherVar = B1;

It gives me 

Error   1   error LNK2020: unresolved token (0A00003B) "int mach_plugin::B1" (?B1@mach_plugin@@3HA) E:\mach_vmotion\Plugin.obj  mach_vmotion
Error   2   error LNK2020: unresolved token (0A00000E) "int mach_plugin::B1" (?B1@mach_plugin@@3HA) E:\mach_vmotion\Form1.obj   mach_vmotion
Error   3   error LNK2001: unresolved external symbol "int mach_plugin::B1" (?B1@mach_plugin@@3HA)  E:\mach_vmotion\Form1.obj   mach_vmotion
Error   4   error LNK2001: unresolved external symbol "int mach_plugin::B1" (?B1@mach_plugin@@3HA)  E:\mach_vmotion\Plugin.obj  mach_vmotion
Error   5   error LNK1120: 3 unresolved externals   E:\mach_vmotion\Debug\mach_vmotion.dll  mach_vmotion

Upvotes: 1

Views: 629

Answers (3)

kwjsksai
kwjsksai

Reputation: 347

inside Form1.cpp. Try

#include "Form1.h"
namespace mach_plugin{
BOOL B1 = TRUE ;
}

You need to post more codes so that we may see it clearly.

Upvotes: 0

jerry
jerry

Reputation: 2611

In general, don't try to assign to variables in header files. Whether you put these assignments before or after the extern BOOL B1 (or deleted that line entirely), it won't work correctly. Instead, assign B1 and SomeOtherVar where they're defined (either via initialization or inside a function).

Upvotes: 0

Balog Pal
Balog Pal

Reputation: 17163

The error message indicates you have something like :

namespace mach_plugin {
#include "form1.h"
}

while your B1 is defined at global scope. Make up your mind where it belongs and make the declaration in header match -- and avod including files inside any blocks, namespace, extern "C", whatever.

Upvotes: 2

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