Iphone substring causing memory leak

Question

Hi All, Im just wrapping up my app, so im onto the stage of running instruments to identify leaks in the app. Ive come across a leak that I cannot work out why it is being registered as a leak.

I have the following lines for example:

NSString *imageType = [[[NSString alloc] initWithString:[loopString substringToIndex:[loopString rangeOfString:@"</IMAGE>"].location]] autorelease];
imageType = [imageType substringFromIndex:[imageType rangeOfString:@"<IMAGE>"].location + :@"<IMAGE>".length];

So basically all im doing is pulling out a section of the "loopstring" and putting that into the imagetype string than just cutting off the trailing fluff of the string using the SubstringFromIndex method.

When I run instruments it says "NSCFString substringwithRange" leak. It highlights the second line:

imageType = [imageType substringFromIndex:[imageType rangeOfString:@"<IMAGE>"].location + :@"<IMAGE>".length];

I would think the substringFromIndex method should return a string that is automatically added to the autorelease pool.

Any ideas on where im going wrong?

Thanks

Following is the refactored code:

- (void)SetupTop10:(NSString *)Top10Data
{
while (Top10Data != @"") {
    NSLog(Top10Data);
    if ([Top10Data rangeOfString:@"</TOP10ENTRY>"].location == NSNotFound){
        Top10Data = @"";
    }
    else
    {

        NSString *loopString = [Top10Data substringToIndex:[Top10Data rangeOfString:@"</TOP10ENTRY>"].location + 13];
        Top10Data = [Top10Data stringByReplacingOccurrencesOfString:loopString withString:@""]; 

        //NOW CREATE A RECORD FOR THIS ITEM
        NSString *imageType = [loopString substringToIndex:[loopString rangeOfString:@"</IMAGE>"].location];
        imageType = [imageType substringFromIndex:[imageType rangeOfString:@"<IMAGE>"].location + 7];
        NSString *displayText = [loopString substringToIndex:[loopString rangeOfString:@"</DISPLAYTEXT>"].location];
        displayText = [displayText substringFromIndex:[displayText rangeOfString:@"<DISPLAYTEXT>"].location + 13];
        NSString *link = [loopString substringToIndex:[loopString rangeOfString:@"</INTERESTID>"].location];
        link = [link substringFromIndex:[link rangeOfString:@"<INTERESTID>"].location + 12];
        [Top10Images addObject:imageType];
        [Top10Links addObject:link];
        [Top10s addObject:displayText];
        Top10RowCount = Top10RowCount + 1;
    } 
}

[self.Top10Table reloadData];
Top10Table.hidden = NO;
loadingLabel.hidden = YES;
loadingIndicator.hidden = YES;

}

//********

Answer 1

It doesn't look leaky. But why

NSString *imageType = [[[NSString alloc] initWithString:
             [loopString substringToIndex:[loopString
                                             rangeOfString:@"</IMAGE>"].location]
         ] autorelease];

if you effectively get the same with

NSString *imageType = [loopString substringToIndex:[loopString
                                             rangeOfString:@"</IMAGE>"].location];

with half the memory usage?

Answer 2

Leaks will tell you where the leaked memory was allocated. If you click around (there's a right-arrow icon by the memory address, I think) then you can look at all the allocations/retains/releases for that addresses.

In this example, Leaks will point you to the first line, when it's the fifth one that "leaks" (actually it's a missing release in dealloc/on assignment that leaks):

NSString * s = [someString substringFromIndex:1];
[myArray addObject:s];
// ...
NSString * s2 = [myArray lastObject];
instanceVariable = [s2 retain];
// ... and forget to release in dealloc

What does tableView:cellForRowAtIndexPath: do?

Answer 3

I can't see any problem in the above code. Did you release Top10Images in your dealloc method?