External Variables

refer to  Addison Wesley - Programming.in.ObjectiveC.2.0.2nd (2009)

#import “ Foo.h ”
int gGlobalVar = 5;
int main (int argc, char *argc[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
Foo *myFoo = [[Foo alloc] init];
NSLog (@ ” %i “ , gGlobalVar);
[myFoo setgGlobalVar: 100]
NSLog (@ ” %i ” , gGlobalVar);
[myFoo release];
[pool drain];
return 0;
}

// method 放在另外一個檔案
-(void) setgGlobalVar: (int) val
{
extern int gGlobalVar; // 必須定義 extern　
gGlobalVar = val;
}