addObject in NSMutableArray doesn't work

I'm a beginner to XCode.

Below is my code. I want to add an object to a mutablearray. From the debugger window I can see there is one object added to the array "words". I can also see the property "flag" of that object is "NO". The problem is another property "str" is shown as "out of scope".

Can anyone help me with this issue? Thanks a loooooot! Stucked on this one for the whole afternoon.

NSMutableArray * words=[[NSMutableArray alloc] initWithCapacity:numberOfWords];

Word *w=[[Word alloc] init];    

[w setStr:@"开发者_Go百科abc" flag:NO];

[words addObject: w];

[w release];

--

@interface Word : NSObject{
    NSString *str;
    BOOL flag;
}

-(void) setStr: (NSString  *) s flag:(BOOL) b
{
    self.str=s;
    flag=b;
}

Do you have a property declaration for your string? Are you retaining the string you are setting?

Still AFAIK 'out of scope' does not necessarily mean it was not set or that nothing has been set. Try an NSLog of the value or something. You might find that there is nothing wrong.

Have a look at this question that talks about scope in GDB:

Objective-C: instance variables out of scope in debugger

Your problem is that the string @"abc" is a temporary object who's scope only exists during the [w setStr:@"abc" flag:NO] method call. You should be able to resolve this problem by making str a @property of Word:

@interface Word : NSObject{
    NSString *str;
    BOOL flag;
}
@property (retain) NSString* str;
@end

And in your implementation file

@implementation Word
@synthesize str;
-(void) setStr: (NSString  *) s flag:(BOOL) b
{
    self.str=s;
    flag=b;
}
@end