NSArray objects go out of scope after returning pointer

Question

I am attempting to use the below code in a function to return an array of dictionary objects. Unfortunately, after the return to the next function in the stack all of the rows in the mutable array have become 'out of scope'. From my understanding, the array should retain the row (dictionary) object automatically so even after the return, where the row pointer goes out of scope, the row objects should still have a retain count of 1. What am I doing wrong here? How do I build this array in such a way that the objects it contains don't get released?

for (int i = 1; i < nRows; i++)
{
  NSMutableDictionary* row = [[[NSMutableDictionary alloc] initWithCapacity:nColumns] ];
  for(int j = 0; j < nColumns; j++)
  {
    NSString* key = [[NSString stringWithUTF8String:azResult[j]] ];
    NSString* value = [[NSString stringWithUTF8String:azResult[(i*nColumns)+j]] ];

    [row setValue:value forKey:key];
  }
  [dataTable addObject:row];
}

return dataTable;

Please reformat that code (for readablity) and show us how you create and maintain the dataTable. — Daniel Bleisteiner
– Daniel Bleisteiner, Commented Aug 28, 2010 at 9:09
Why do you mean by 'out of scope'? Why do you use NSMutableDictionary in such a strange way? — unbeli
– unbeli, Commented Aug 28, 2010 at 9:15
looks like you got a memleak for row, when row is added to dataTable the retain count goes up with one but it is already one through the alloc/init, you should allocate row using dictionaryWithCapacity instead — AndersK
– AndersK, Commented Aug 28, 2010 at 9:30

Krešimir Prcela · Accepted Answer · 2010-11-18 21:25:10Z

1

This line:

NSMutableDictionary* row = [[NSMutableDictionary alloc] initWithCapacity:nColumns] ];

should use the autorelease:

NSMutableDictionary* row = [[[NSMutableDictionary alloc] initWithCapacity:nColumns] ] autorelease];

answered Nov 18, 2010 at 21:25

Krešimir Prcela

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Comments

Leg10n · Accepted Answer · 2010-08-28 20:07:38Z

From what i understand:

-(NSMutableArray*) getArrayOfDictionaries{
    int nRows=somenumber;
    int nColumns=someOthernumber;
    char **azResult=someArrayOfStrings;

    NSMutableArray *dataTable=[[NSMutableArray alloc] init];
    for (int i = 1; i < nRows; i++)
    {
      NSMutableDictionary* row = [[[NSMutableDictionary alloc] initWithCapacity:nColumns]];
      for(int j = 0; j < nColumns; j++)
      {
        NSString* key = [[NSString stringWithUTF8String:azResult[j]] ];
        NSString* value = [[NSString stringWithUTF8String:azResult[(i*nColumns)+j]] ];

        [row setValue:value forKey:key];
      }
      [dataTable addObject:row];
      //you should add the following line to avoid leaking
      [row release];
    }

    //watch for leaks
    return [dataTable autorelease];
    //beyond this point dataTable will be out of scope
}

-(void) callingMethod {
    //dataTable is out of scope here, you should look into arrayOfDictionaries variable
    NSMutableArray* arrayOfDictionaries=[self getArrayOfDictionaries];
}

You should look into the local variable in callingMethod instead of dataTable which is local to the method I called getArrayOfDictionaries

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