Problem in memory manegment?

Question

Hi, I developing an application, in which i working with database manipulation. The method i have written in database class as follows.

-(NSMutableArray *)getData: (NSString *)dbPath{
    NSMutableArray *dataArray = [[NSMutableArray alloc] init];

    if(sqlite3_open([dbPath UTF8String], &database) == SQLITE_OK){
        NSString *sqlQuery = [NSString stringWithFormat:@"SELECT empID, addText FROM Employee WHERE nameID = %@", nameID];
        sqlite3_stmt *selectstmt;
        if(sqlite3_prepare_v2(database, [sqlQuery UTF8String], -1, &selectstmt, NULL) == SQLITE_OK){

           while (sqlite3_step(selectstmt) == SQLITE_ROW){
                [dataArray addObject:[[NSMutableDictionary alloc] init]];

                [[dataArray lastObject] setObject:[NSString 
                                 stringWithFormat:@"%d", sqlite3_column_int(selectstmt, 0)] forKey:@"empID"];

                [[dataArray lastObject] setObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt,1)] forKey:@"addText"];
            }
        }

        sqlite3_finalize(selectstmt);
    }
    sqlite3_close(database);
    return dataArray;
}

The above code work fine on the simulator but cannot on device. I also was tracing the memory leaks , in which i founding that memory leak in above method code. But i not able to solve the that memory leak.

Now i also find out memory leak in following method.

• (id)initWithString:(NSString *)str attributes:(NSDictionary *)attributes

{ if ((self = [super init])) { _buffer = [str mutableCopy]; _attributes = [NSMutableArray arrayWithObjects:[ZAttributeRun attributeRunWithIndex:0 attributes:attributes], nil]; } return self; }

The leak near _buffer = [str mutableCopy];. And leak trace gives me in the output continuous increasing NSCFString string allocation. How i maintain it?

Thanks in advance.

Answer 1

Your leak is that you don't release either the dataArray object, nor the mutable dictionaries you create in the while loop. Consider autoreleasing the mutable array, and manually releasing the dictionaries after you add them to the array.

As for why it "doesn't work" on the device, you need to be more specific about what happens and why that isn't what you expect.

Answer 2

From the first glance you have 2 places where leaks can be:

NSMutableArray *dataArray = [[NSMutableArray alloc] init];
...
return dataArray;

Caller method is responsible for releasing array returned from your method - check if it does.

Also your method name is not consistent with obj-c guidelines - they suggest that methods returning non-autoreleased object( so caller is responsible for releasing them) should contain create, alloc, copy in their name. So it could be better to return autoreleased array (return [dataArray autorelease]; from this method and let caller decide whether it needs to retain array or not.

Second place is

[dataArray addObject:[[NSMutableDictionary alloc] init]];

It is leaking dictionary object, you should probably just write

[dataArray addObject:[NSMutableDictionary dictionary]];

Answer 3

Your inner loop leaks the NSMutableDictionary objects, as you should release them after adding to the array, i.e.

NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setObject:[NSString  stringWithFormat:@"%d", sqlite3_column_int(selectstmt, 0)] forKey:@"empID"];
[dict setObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt,1)] forKey:@"addText"];
[dataArray addObject:dict];
[dict release];

Also, your whole method should most probably return an autoreleased object by naming convention. Not sure if this is a leak - depends on how you call that method and if you release the returned value.

So maybe use

return [dataArray autorelease];

Answer 4

Your method contains two call to +alloc that don't have corresponding calls to -release or -autorelease.

NSMutableArray *dataArray = [[NSMutableArray alloc] init];
...
[dataArray addObject:[[NSMutableDictionary alloc] init]];

You can rewrite these lines like this to get rid of the leak:

NSMutableArray *dataArray = [NSMutableArray array];
...
[dataArray addObject:[NSMutableDictionary dictionary]];