Re: Cocoa programming

FROM : Joachim Haagen Bøe
DATE : Sat Nov 09 18:13:01 2002

Thanks for all your reply guys and girls! That was really helpful!

Cheers,
Joachim

On Saturday, November 9, 2002, at 11:41 PM, Andreas H=F6schler wrote:

> Hi,
>

>> Question 1 - pointers
>>
>> I understand that * means the the variable is a pointer, and to me it =

=20
>> seems as if ALL complex variables are pointers (im up to chapter 4 in =

=20
>> the book). Is this the case?

>
> Yes!. If you allocate an object - e.g. NSString *string =3D =20
> [[NSMutableString alloc] init]; - ram space for the object is =20
> allocated (usually only a few bytes) and a pointer to this space is =20=


> returned. This pointer is used to address the object. This pointer is =20=


> also the target for messages, e.g. int length =3D [string length]. =

This =20
> corresponds to string.length in Java.
>

>> And is passing a pointer as a parameter to a method the same as =20
>> passing a complex variable to a method in Java ?

>
> Yes!
>

>> Question 2 - @, %, %@ and %d
>>
>> When creating NSStrings I see a lot of these symbols. I have figured =20=


>> out that you specify which variables go into these symbols, but have =20=


>> the following question regarding the following code:
>>
>> outputString =3D [NSString stringWithFormat:@"%@ has %d letters", =20
>> inputString, [inputString length]];
>>
>> What is the very first @ for?
>> Why is the second %@, and not $d ?

>
> The second is %d and the first is %@, right?
>

>> What is the difference between %@ and %d ?

>
> %d is a placeholder for int, unsigned,... %@ is a placeholder for an =20=


> Objective-C object. This object is automatically send the message =20
> "description" which is supposed to return an NSString. So you can pass =

=20
> NSNumber, NSDeciamlNumber, NSString,... (all objects that respond to =20=


> description) as a parameter for a %@ placeholder.
>

>> Okay, thats my main difficoulties, other than the whole [] instead of =

=20
>> .'s in the notation.

>
> ... which is genial by the way. Consider the following method of =20
> NSCalendarDate.
>
> - (NSCalendarDate *)dateByAddingYears:(int)year months:(int)month =20
> days:(int)day hours:(int)hour minutes:(int)minute seconds:(int)second
>
> You call it as follows.
>
>     NSCalendarDate *date; // Assume this object exists
>
>     [date dateByAddingYears:0 months:3 days:15 hours:2 minutes:30 =20=


> seconds:0];
>
> Try this in Java or C++. It would look like.
>
>     =20
> =

date.dateByAddingSomeStuffNoBodyKnowsHowToCallThisMethod(0,3,15,2,30,0)=20=

> ;
>
> What is easier to read?
>

>> Im sorry about the very basic questions, but I'd appreciate if anyone =

=20
>> took the time out of their busy schedual to answer some of these.

>
> You are welcome!
>
> Regards,
>
>    Andreas