Question

I have declared a global variable like below

extern NSString *name;
@interface viewcontrollerOne{}

in implementation file i am accessing that global variable in some method like

-(void)someMethod
{
name = @"hello";
}

but this is giving linker error.

“name”, referenced from:
-[viewcontrollerOne someMethod] in viewcontrollerOne.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

The following is merely a declaration:

extern NSString * const name; // << side note: this should typically be const

It declares there is a symbol of NSString* named name. It does not create storage.

To do that, you will need to provide a definition for name. To do this, add the following to your .m file:

NSString * const name = @"hello";

---

If you want to set it in an instance method, as seen in your example, then you can declare it:

MONFile.h

extern NSString * name;

Define it:

MONFile.m

NSString * name = 0;

then you can write name = @"hello"; in your instance method.