Re: Another memory question
Re: Another memory question
- Subject: Re: Another memory question
- From: Glen Simmons <email@hidden>
- Date: Tue, 26 Aug 2003 14:54:25 -0500
On Tuesday, August 26, 2003, at 01:53 PM, James Ludtke wrote:
In the code fragment below I reassign a new value to an
NSString. (I have seen others do that as well.)
- (void)awakeFromNib {
NSString *demoFile;
demoFile = [NSString stringWithString: @"~/Application User
Data/dsf.plist"];
demoFile = [demoFile stringByExpandingTildeInPath];
// more code
}
If I have understood it correctly, the second assignment creates
a new memory block for the string, and the first string is still
in memory, but can no longer be accessed.
It can no longer be accessed by *you*, but it has been added to the
autorelease pool before being returned to you.
My questions are:
1) Will the auto release process release the first block or
will there be a memory leak?
No memory leak - autorelease is your friend.
2) Is the above example good practice, or would the following
have been better:
Umm, not quite.
- (void)awakeFromNib {
NSString *demoFile;
NSString *temp = [[NSString alloc] init];
You've alloced a new object, so you're responsible for releasing it.
temp = [NSString stringWithString: @"~/Application User
Data/dsf.plist"];
Here, you assign the address of another object to the pointer variable
temp, thus losing your reference to the original object. This causes a
leak. This new object is autoreleased before it's returned to you, so
you shouldn't release it.
demoFile = [temp stringByExpandingTildeInPath];
A third object is created, autoreleased and returned and you've
assigned it to demoFile.
[demoFile release];
You now release demoFile which you haven't alloced, copied or retained.
When the autorelease pool is released, this app will crash. This is a
somewhat difficult bug to track down as the crash does not happen close
to the actual bug.
// more code
}
I'd suggest reading some more about Cocoa memory management. Most
people seem to overthink it when they are starting. It's (usually)
quite easy. Try
http://www.stepwise.com/StartingPoint/Cocoa.html,
specifically the "Cocoa Basics" section.
HTH,
Glen
_______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.