Why doesn't NSString getCharacters work in xcode?

-(void)myFunction {

        unichar myBuffer[5];
        NSRange range = {0, 3};
        NSString *string = [NSString alloc];
        string = @"123";
        [string getCharacters:myBuffer :range开发者_如何转开发];
}

Gets warning

! NSString may not respond to '-getCharacters::'

then does a SIGABRT when I run it. Why????? Or better yet how can I get it to work?

To use getCharacters:range:, write this line of code:

[string getCharacters:myBuffer range:range];

In Objective-C, method names are split up by arguments (a feature that derives from its Smalltalk heritage). So your original code was trying to send a message that's essentially named getCharacters: :, which isn't found. The corrected version sends the message getCharacters: range:.

The getCharacters:myBuffer construct says that the first argument to getCharacters:range: is myBuffer. Similarly, the range:range construct says the second argument is your NSRange named range.