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If you create an object using a method that begins with init, new, copy, or mutableCopy, then you own that object and are responsible for releasing it (or autoreleasing it) when you're done with it. If you create an object using any other method, that object is autoreleased, and you don't need to release it.
A static, plain-text Unicode string object which you use when you need reference semantics or other Foundation-specific behavior.
Once a string has been initialized using NSString, the only way to append text to the string is to create a new NSString object. While doing so, you can append string constants, NSString objects, and other values.
You use it with @"%@%@" to concatenate two strings, @"%@%@%@" to concatenate three strings, but you can put any extra characters inside, print numbers, reorder parameters if you like and so on.
I was playing with the respondsToSelector method in Objective-C on MacOS-X 10.6.7 and Xcode 4.0.2, to identify if an object would respond to certain messages. According to the manuals, NSString should not respond to appendString: while NSMutableString should. Here's the piece of code which tests it:
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString *myString = [[NSString alloc] init];
if ([myString respondsToSelector:@selector(appendString:)]) {
NSLog(@"myString responds to appendString:");
} else {
NSLog(@"myString doesn't respond to appendString:");
}
// do stuff with myString
[myString release];
[pool drain];
return 0;
}
and here's the output:
Class02[10241:903] myString responds to appendString:
I'd sort of expected the opposite. How does an NSString object respond to appendString: ? What's going on here that I'm missing ?
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