What characters does a new empty NSString contain?

i created an NSMutableString with t开发者_JAVA技巧he method stringWithCapacity:5 How do i test if characterAtIndex:0 is empty

Empty string contains no characters, even if you created it with non-zero capacity. To check if string is empty simply check its length:

if ([myString length] == 0){
    // empty
}

Moreover, trying to access a character at index which is >= of string's length will result in NSRangeException exception.

The *WithCapacity methods that we see on NSString, NSArray, etc, have nothing to do with pre-populating the contents of the object. They are simply a means by which you can suggest to the object how much it's going to hold. If you suggest a large enough number, it may use a different storage mechanism than if it were a small number.

So in other words, you could do [NSMutableString stringWithCapacity:1234567890] and it give you exactly the same thing as if you had simply done [NSMutableString string], and the -length of the resulting object will always be 0.

Frankly, the *WithCapacity methods are pretty useless. I've never found a reason to use them.