Question

another memory management question:
I have asked this before, but did not really get an answer:

The question is would the following result in a leak or is it ok?

NSArray *txtArray = [NSArray array];

NSString *aTxtFieldTxt = [[NSString alloc]initWithString:aTxtField.text];
aTxtFieldTxt = [aTxtFieldTxt stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];


NSMutableString *aTxt = [[NSMutableString alloc]initWithString:aTxtFieldTxt];
[aTxtFieldTxt release];


txtArray = [aTxt componentsSeparatedByString:@" "];

aTxt = [[txtArray objectAtIndex:0] retain];


for(int i = 1; i < [txtArray count]; i++){

   [aTxt appendString:@"+"];
   [aTxt appendString:[[txtArray objectAtIndex:i]retain]];
}

This is part of a function. And I am not sure if the assignment of aTxt = [[txtArray objectAtIndex:0] retain]; causes a leak because it is a pointer which originally points to

NSMutableString *aTxt = [[NSMutableString alloc]initWithString:aTxtFieldTxt];
[aTxtFieldTxt release];

How do I do this correctly. Would I have to use another pointer? Can somebody please explain this issue?

Thanks alot!

Answer 1

Lots and lots of issues with this code.

//
// Don't do this.  Just declare the txtArray
//
NSArray *txtArray /* = [NSArray array]*/;

//
// You need to auto release after init in this case.
//
NSString *aTxtFieldTxt = [[[NSString alloc]initWithString:[aTxtField text]] autorelease]; 

//
// You are reassigning the aTxtFieldTxt and the new value is returned autoreleased.
//
aTxtFieldTxt = [aTxtFieldTxt stringByTrimmingCharactersInSet:[NSCharacterSet  whitespaceAndNewlineCharacterSet]];

//
// Again, autorelease after init
//
NSMutableString *aTxt = [[[NSMutableString alloc]initWithString:aTxtFieldTxt] autorelease]; 

//
// You never alloced this instance so it needs no release.
//
 /*[aTxtFieldTxt release]; */

//
// This array is returned autoreleased
//
txtArray = [aTxt componentsSeparatedByString:@" "];

//
// No need to retain here.  Just get the object
//
aTxt = /*[*/[txtArray objectAtIndex:0]/* retain]*/;

for(int i = 1; i < [txtArray count]; i++)
{
    [aTxt appendString:@"+"]; 
    [aTxt appendString:[[txtArray objectAtIndex:i]retain]]; 
}

I have found, that if you have retains/releases outside of accessors/base int/dealloc routines, you are doing something wrong. For every alloc you must have a balanced release/retain for that instance of the object. If you reassign the variable, you will loose your reference to it.

This is a quick stab on how I would write this code:

NSArray         *txtArray;
NSString        *aTxtFieldTxt = [NSString stringWithString:[aTxtField text]];
NSMutableString *aTxt;

aTxtFieldTxt = [aTxtFieldTxt stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
aTxt         = [NSMutableString stringWithString:aTxtFieldTxt]; 
txtArray     = [aTxt componentsSeparatedByString:@" "];

aTxt = [NSMutableString stringWithString:[txtArray objectAtIndex:0]];
for(int i = 1; i < [txtArray count]; i++)
{
    [aTxt appendString:@"+"]; 
    [aTxt appendString:[[txtArray objectAtIndex:i]retain]]; 
}