Question

I am getting a EXC_BAD_ACCESS (SIGBUS) on this line in my iPhone project:

if (timeoutTimer) [timeoutTimer invalidate]; 

The thing that has me stumped is that I don’t understand how that line could crash, since the if statement is meant to be checking for nil. Am I misunderstanding the way Objective-C works, or do line numbers in crash statements sometime have the wrong line in them?

Answer 1

Just because a variable is set to a value other than nil doesn’t mean it’s pointing to a valid object. For example:

id object = [[NSObject alloc] init]; [object release]; NSLog(@'%@', object); // Not nil, but a deallocated object,                       // meaning a likely crash 

Your timer has probably already been gotten rid of (or possibly hasn’t been created at all?) but the variable wasn’t set to nil.