Describe GlobalVariable

Can someone tell me how global variable works in Project Builder v2.1 on MAC OS X10.2.8? I have declared a NSMutableArray as global variable in OS X10.3, and it works fine. But when I move to OS x10.2.8 and declare the global variable in the same way, it gives me a error saying “multiple definitions of symbol”. I am not sure what is going on, can someone help me out here? Thanks.

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To declare a GlobalVariable, put this in the .h file:

extern YourTypeHere gGlobalVariable;

And in the .m file:

YourTypeHere gGlobalVariable = initial_value;

Now that you know how, please please please reconsider using one. GlobalVariables are almost never the right solution. Make a static global with accessor methods on a class somewhere, or something. Use of a GlobalVariable can make life very hard, very fast.

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Global variables are often appropriate for items that you treat as constant. For example, Apple’s notification names are global variables.

Constant NSString declaration: header file

extern NSString* const TJHConstantString;

source file

NSString* const TJHConstantString = @”SomeString”;

TJHConstantString can not be reassigned without getting a compiler error.