Question

I’m beginner ObectiveC user so please keep potential answers simple.
I have quite a few years experience with C and C++.

Now, with ObjectiveC I want to create two objects, not using properties. My question is “what is wrong here” not “how to do it differently”.
So there is my code:

@implementation News

NSString *_title;
NSString *_excerpt;
NSString *_content;
NSString *_thumbnailURL;
NSString *_date;

-(id)initWithTitle:(NSString *)title excerpt:(NSString *)excerpt content:(NSString*)content thumbnail:(NSString *)thumbnailURL date:(NSString *)date {
    self = [super init];
    if (self) {
        _title = [[NSString alloc] initWithString:title];
        _excerpt = [[NSString alloc] initWithString:excerpt];
        _content = [[NSString alloc] initWithString:content];
        _thumbnailURL = [[NSString alloc] initWithString:thumbnailURL];
        _date = [[NSString alloc] initWithString:date];
    }
    return self;
}

-(void)showData {
    NSLog(@"    title:%@", _title);
    NSLog(@"    excerpt:%@", _excerpt);
    NSLog(@"    thumbnailURL:%@", _thumbnailURL);
    NSLog(@"    date:%@",  _date);
    NSLog(@"    getContent:%@", _content);
}
@end    

Now I want to create two objects:

News *nws = [[News alloc] initWithTitle:@"title1" excerpt:@"excerpt1" content:@"content1" thumbnail:@"thumbnail1" date:@"date1"];
News *nws2 = [[News alloc] initWithTitle:@"title3" excerpt:@"excerpt3" content:@"content3" thumbnail:@"thumbnail3" date:@"date3"];

After that want to show whats is inside this objects:

[nws showData];
[nws2 showData];

Result is that both objects have the same values inside. All ended with “3”. I thought that nws object will containt values ending with “1” and nws2 will contain values with “3”. But it isnt working like that. Why? Where is an error?
Please help and thanks!

Answer 1

I asked in twitter and got the following comment from @Bavarious:

https://gist.github.com/11c22c0edea5391a3799 (bold added)

Any variable declared outside of @interface … {} or @implementation … {} is treated as a regular C variable.
In your example, _excerpt
is a global (file scope) variable with static storage duration and
could equivalently be placed at the top of the file before
@interface, or between @interface and @implementation, or
between the implementation of two methods — it’s the same mechanism
where file scope variables in C are defined outside of a function
block.

Variables with static storage duration can be used to realise class
variables, a concept that doesn’t exist in Objective-C.