Re: Basic Obj-C Question on Memory and Strings
Re: Basic Obj-C Question on Memory and Strings
- Subject: Re: Basic Obj-C Question on Memory and Strings
- From: Charles Steinman <email@hidden>
- Date: Fri, 8 Aug 2008 00:01:24 -0700 (PDT)
--- On Thu, 8/7/08, Matt Keyes <email@hidden> wrote:
> -(void)foo {
> SomeClass *cls = [[SomeClass alloc] init];
> [cls DoTheStringThing:@"Here's a fun
> string."];
>
> //HERE IS THE QUESTION:
> //This causes a halt in the debugging and will
> sometimes give a _BAD_ADDRESS or something... simply
> checking the NSString pointer causes it
> //I am having a hard time I guess understanding Obj-C
> memory management b/c in traditional C/C++ this would be
> fine to do
> if(cls.someString)
> {
> self.txtMyTextBox.text = [[NSString alloc]
> cls.someString];
> }
> }
This would not be fine in C++. The alloc/init pair is roughly equivalent to C++'s new operator. Here's a somewhat equivalent method in C++:
void foo() {
SomeClass *cls = new SomeClass;
if (cls.getSomeString()) {
string tempString = cls.getSomeString();
this.getTxtMyTextBox().setText((malloc(sizeof(string))).tempString());
}
}
You're trying to take a string property and send it as a message to an uninitialized object, and then take the result of this non-method and assign it to a property of another object. The odd thing is that it compiles at all. I suggest you reread the Objective-C memory management docs.
http://developer.apple.com/documentation/Cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html
You might also try working through some basic Cocoa tutorials to give you a feel for how Cocoa programming works before you set out on your own. Besides memory management, you seem a bit unclear on Obj-C's message syntax. It's unfamiliar, but not really that hard. If you take it slow for a little bit, I think everything will become clear pretty quickly.
Cheers,
Chuck
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