value of Bool in Objective C

Question

The value of BOOL in objective C is always NO(by default). But recently I encountered a case where the value of BOOL variable was returning YES (by default). Can anybody explain this to me ?

Answer 1

Perhaps someone redefined their values?

#define YES (BOOL)0
#define NO  (BOOL)1

Answer 2

BOOL has no value as it is a type.

You probably mean variables of type BOOL. There are different types of variables, which have different initialization semantics:

1. Instance variables: Objective-C's alloc promises to set all instance variables to zero, which in case of BOOL means NO;
2. Global variables: Or, more precisely, variables with static storage duration are initialized to zero, as defined in the C standard.
3. Local variables are not initialized. If you don't assign a value, their contents are undefined. This is also from the C standard and probably what you stumbled upon.