How to release a string created inside a method? - ios

Question

I have declared a local string inside the method. I am releasing the string inside the same method. I found my code crashing if release that object. If I don't release the string, code runs successfully.
I have called that method in viewdidappear so that method is called while pushing and poping. Nothing gets printed in the console. Here is my code
-(void)appendString{
NSString *locStr = [[NSString alloc] initWithString:#""];
for (int i=0;i<[result count]; i++)
{
locStr=[locStr stringByAppendingFormat:#"%#",[result objectAtIndex:i]];
}
[str setString:locStr];
[locStr release];
}
I am calling the "appendString" method from "viewDidAppear"."str" is a NSMutable string declared in .h class.How should I release the "locStr".
What went wrong in my code? This isn't the normal way to release it?

Answer 1

Try this:
-(void)appendString{
//stringWithString returns an autorelease object
//so you don't need to worry about its memory management
NSString *locStr = [NSString stringWithString:#""];
for (int i=0;i<[result count]; i++)
{
//if your locstr is created by initWithString instead,
//the following line is going to cause memory leak
locStr=[locStr stringByAppendingFormat:#"%#",[result objectAtIndex:i]];
}
[str setString:locStr];
//[locStr release];
}
And make sure that the string property in your str instance is set to retain

Answer 2

You may want to use NSMutableString and not create multiple string objects that may or may not release at some time in the distant future.
-(void)appendString
{
NSMutableString *locStr = [[NSMutableString alloc] initWithString:#""];
for (int i=0;i<[result count]; i++)
{
[locStr appendFormat:#"%#",[result objectAtIndex:i]];
}
[str setString:locStr];
[locStr release];
}
see

Answer 3

In your code, calling [locStr release] is sent to the NSString instance returned from [locStr stringByAppendingFormat:#"%#",[result objectAtIndex:i]] That code actually returns a new String instance, so your variable locStr is now pointing to that new NSString instance and your reference to the original one is lost.
So it is NOT the instance of the NSString you created with [[NSString alloc] initWithString:#""]
The NSString returned from stringByAppendingFormat is autoreleased and your [locStr release] would over-release it. As the other answers indicate you could just use a NSMutableString to avoid lots of NSString instances to be created in your loop and actually releasing the original created instance.

Answer 4

No need to alloc/init locStr. This should do the trick:
-(void)appendString{
NSString *locStr = #"";
for (int i=0;i<[result count]; i++) {
locStr=[locStr stringByAppendingFormat:#"%#",[result objectAtIndex:i]];
}
[str setString:locStr];
}

Answer 5

Don't release, use autorelease. This is the way if you need to return something. When there is an autorelease pool (which is in most cases) it is released automatically. That's what methods like stringByAppendingFormat do also.
Or wait, when you di something like this, it is important, that you retain the Object in the setter Method. It is better then to use a property like
{
NSString* thestring;
}
#property (nonatomic, retain) NSString* thestring;
and a
#synthesize thestring;
in the .m file.

Answer 6

use this
locStr=[[locStr stringByAppendingFormat:#"%#",[result objectAtIndex:i]] retain];
then you can release this same as you are doing.
what happens here you get an autorelease object of string by stringByAppendingFormat method.
so you need to convert it into a retain copy.