26 April 2007
malloc: *** Deallocation of a pointer not malloced: 0×500120; This could be a double free(), or free() called with the middle of an allocated block; Try setting environment variable MallocHelp to see tools to help debug
I keep on getting this error all afternoon when a Cocoa application. It basically means ‘you are releasing something twice’. e.g.
WRONG!
... //lovely code ...
[object release];
... //lovely code making you forget things ...
[object release];
CORRECT!
... //lovely well behaved code ...
[object release];
... //lovely well behaved code not at all requiring a garbage collector.
I don’t know about how to use the apple developer tools to find this bug in the code, I just found it my trail and error. If you know how, let me know.
3 Comments currently posted.
Chinmoy says:
boyfarrell says:
Hi,
It never occurred to me to set the method to nil. That could be a good problem solving method. Cheers for the link.
Dan.
Chinmoy says:
Actually, I can’t take credit for setting the pointer to nil, because I read that in Aaron Hillegass’s book, Cocoa Programming for Mac OS X 
Chinmoy.
Hi Daniel,
You could use MallocDebug (see http://developer.apple.com/tools/performance/overview.html#mallocdebug) to find memory allocation related problems. MallocDebug is a standalone app that comes with the CHUD(Computer Hardware Understanding Development Tools) that you can download from Apple’s Developer Connection.
You could also add this trick after a call to release:
[object release]; //this is your first release
object = nil;
[object release]; //same as [nil release];
//nothing happens.
//actually something might happen, but
//not another release.