Question

the following code crashes.Basically i am accessing a very large string(xml -contains image data) saved as a file…modifying it and saving it in a new name… when profiling i didnot see any leak with this code… but after repeating this process for 20-25 times… the app crashes on iphone 3gs with memory warning level three and it kills the whole apps running too… i cant find any place where this app is leaking to cause a memory warning ….any suggestions

NSAutoreleasePool *pool=[[NSAutoreleasePool alloc] init];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
 NSString *documents = [paths objectAtIndex:0];
 NSString *filename = [NSString stringWithFormat:@"%@.yyy",fileToDuplicate];
 NSString *initPath = [documents stringByAppendingPathComponent:filename];
 NSString *final = [NSString stringWithFormat:@"%@.yyy",[[alertView textFieldAtIndex:0] text]];
 NSString *finalPath = [documents stringByAppendingPathComponent:final];
 NSString *newName=[[[alertView textFieldAtIndex:0] text] copy];
 NSError *error;
 NSString *xml = [[NSString alloc] initWithContentsOfFile:initPath encoding:NSASCIIStringEncoding error:&error] ;
 NSString *xml_1=[xml stringByReplacingOccurrencesOfString:[NSString stringWithFormat:@"<file_name><name>%@.yyy</name></file_name>",fileToDuplicate] withString:[NSString stringWithFormat:@"<file_name><name>%@.yyy</name></file_name>",newName]];
NSString *xml_2=[xml_1 stringByReplacingOccurrencesOfString:[NSString stringWithFormat:@"<property_name>%@</property_name>",fileToDuplicate] withString:[NSString stringWithFormat:@"<property_name>%@</property_name>",newName]];
[xml_2 writeToFile:finalPath atomically:YES encoding:NSASCIIStringEncoding error:&error];
 xml=nil;
 [xml release];
 xml_1=nil;
 xml_2=nil;
 [self.mTableView reloadData];
 fileToDuplicate=@"";
 [newName release];
 [pool drain];
 return ;

Answer 1

If you don’t see where this is leaking then please switch to ARC. It’s as clear as day in the middle:

Alloc xml

Set the variable xml to nil (LEAK!!!!!)

Release the content of xml (which is nil) <— this does nothing

The last two are reversed. You need to release it before you set it to nil. I suggest reading a little more about pointers if you do not understand this concept. The release message acts on the content of the pointer, not the pointer itself. The latter wouldn’t make sense.