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Help accessing static variable from multiple files.

Started by dustamulet Aug 4, 2006 at 10:01 PM 4 replies 550+ views

Original Post

Aug 4, 2006 at 10:01 PM

Hi I have a problem trying to access a static variable contained in the namespace 'NameSpace'. I have 2 classes: IntializeStatic and AccessStatic. InitializeStatic is called first and in the output it gives the correct result. After this, AccessStatic is called and in the output gives an incorrect result. The output produces: Init: 100 Access: 0 When I want it to produce: Init: 100 Access: 100 Can anyone help?? main.cpp

#include <iostream>
#include "InitializeStatic.h"
#include "AccessStatic.h"
using namespace std;
using NameSpace::InitializeStatic;
using NameSpace::AccessStatic;

int main()
{
	InitializeStatic  init;
	AccessStatic      access;

	system( "PAUSE" );
	return 0;
}

InitializeStatic.h

#ifndef INITIALIZESTATIC_H
#define INITIALIZESTATIC_H

#include "AccessStatic.h"
#include <iostream>
using namespace std;
using NameSpace::AccessStatic;

namespace NameSpace
{
	class InitializeStatic
	{
	public:
		InitializeStatic();
	};
}

#endif

InitializeStatic.cpp

#include "InitializeStatic.h"
using NameSpace::InitializeStatic;

InitializeStatic::InitializeStatic()
{
	NameSpace::StaticInt = 100;

	cout << "Init: " << NameSpace::StaticInt << endl;
}

AccessStatic.h

#ifndef ACCESSSTATIC_H
#define ACCESSSTATIC_H

#include <iostream>
using namespace std;

namespace NameSpace
{
	static int StaticInt = 0;

	class AccessStatic
	{
	public:
		AccessStatic();
	};
}

#endif

AccessStatic.cpp

#include "AccessStatic.h"
using NameSpace::AccessStatic;

AccessStatic::AccessStatic()
{
	cout << "Access: " << NameSpace::StaticInt << endl;
}

JohnBolton

132

JohnBolton

Aug 4, 2006 at 10:08 PM

A static (non-member) variable can only be accessed in the file it is defined in. If you have two static variables with the same name in different files, they are different variables. Since you have "static int StaticInt = 0" in the header file, you are defining a static variable named StaticInt in every file the header is included in. Since the variables are static, they are all different variables.

The bottom line is that you can only access a static (non-member) variable in the file it is defined in. So the question is this: What are you trying to do?

dustamulet

Author

dustamulet

Aug 4, 2006 at 10:10 PM

I wanted to keep the StaticInt variable accessible from anywhere by just typing in:

NameSpace::StaticInt;

yadango

Aug 4, 2006 at 10:10 PM

hmmm for something like that wouldn't extern be a better keyword? you could also declare the static int in only one of the cpp files and have functions to access it.

dustamulet

Author

dustamulet

Aug 4, 2006 at 10:19 PM

Quote:
Original post by yadango
hmmm for something like that wouldn't extern be a better keyword? you could also declare the static int in only one of the cpp files and have functions to access it.

Thx I got it working from what you suggested:

1. Add "int NameSpace::StaticInt = 0;" to AccessStatic.cpp
2. Change "static int StaticInt = 0;" to "extern int StaticInt;" in AccessStatic.h

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