Variable Scope issue

haxan · Jan 7, 2010

Hi. I am having an issue with variables and their scope. How can i access variables directly which are in one C file to another C file in the same project?

For example i have two C files, code1.c and code2.c

Some variables that i declared in code1.c i want to use directly into code2.c

Is there anyway to do it?

Example:

code1.c:

unsigned char myVariable = 24;

code2.c:

#include "code1.c"
myVariable = myVariable + 2;

dougy83 · Jan 7, 2010

haxan said:
code2.c:

#include "code1.c"
myVariable = myVariable + 2;

You mean #include "code1.h", right? In code1.h you just declare myVariable as extern. e.g.

Code:

extern unsigned char myVariable;

haxan · Jan 7, 2010

dougy83 said:
You mean #include "code1.h", right? In code1.h you just declare myVariable as extern. e.g.

Code:

extern unsigned char myVariable;

The compiler gives warnings and it still is not working

warning: 'myVariable' initialized and declared 'extern'

haxan · Jan 7, 2010

If i do not initalize it with extern,

it gives the following error from the file it is used from:

undefined reference to `myVariable'

jbmillard · Jan 7, 2010

haxan said:
If i do not initalize it with extern,

it gives the following error from the file it is used from:

Can you post the code? It's hard to tell if you are still including code.c (which you shouldn't be).

dougy83 · Jan 7, 2010

I think you misunderstood.

code1.h (declare the variable as being held somewhere else)

Code:

extern unsigned char myVariable;

code1.c (define and initialise the variable as belonging to this file)

Code:

unsigned char myVariable = 0;

code2.c (includee the extern decl and then do something with the variable from the other file)

Code:

#include "code1.h"
... something ...
myVariable = 33;

haxan · Jan 7, 2010

Thank you, its been solved now.

Following is the correct method for someone who falls in the same place as me.

code1.C:
unsigned char myVariable;
myVariable = 2;

code2.C:
extern volatile unsigned char myVariable;
myVariable = 5;

The code2.c can now access the same variable.

jbmillard · Jan 7, 2010

haxan said:
Thank you, its been solved now.

code1.C:
unsigned char myVariable;

I would probably make this:

Code:

volatile unsigned char myVariable;

so they are declare the same everywhere.

Brad

dougy83 · Jan 7, 2010

I'm guessing the 'volatile' keyword was inadvertently added in the first instance.

jbmillard · Jan 7, 2010

dougy83 said:
I'm guessing the 'volatile' keyword was inadvertently added in the first instance.

You're probably right. Just wanted to make sure.

Variable Scope issue

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