Question

Hi All I have a class that works with sqlite database in my application. Here you can see one of the functions that I have write. This function must get the count of items in witch the column value is equals to the given value.

 + (int) GetCountOfItems: (NSString*) byColumn {
        // Autorelease Pool.
        NSAutoreleasePool* pool = [[NSAutoreleasePool alloc]init];
        // Create Sqlite query string.
        NSString* sqliteQuery = [NSString stringWithFormat:@"SELECT COUNT(*) FROM [Articles] WHERE %@ = 1", byColumn];
        NSLog(@"GetCountOfItems query string is: %@", sqliteQuery);
        // Create statement.
        sqlite3_stmt*   stmt;
        int articleCount = 0;

        if( sqlite3_prepare_v2(database, [sqliteQuery UTF8String], -1, &stmt, NULL) == SQLITE_OK ) {
            if( sqlite3_step(stmt) == SQLITE_ROW )
                articleCount  = sqlite3_column_int(stmt, 0); 
        }
        else NSLog(@"Failed from GetCountOfItems. Error is:  %c", sqlite3_errmsg(database));

        // Finalize.
        sqlite3_finalize(stmt);

        // Release Pool.
        [pool release];

        return articleCount;
    }

I want to know if this function is correct for example should i use NSAutoreleasePool* pool = [[NSAutoreleasePool alloc]init]; ???? And how it can help me with memory ?

Answer 1

Based on the following description (in the Memory Management Programming Guide):

The Application Kit automatically creates a pool at the beginning of an event cycle (or event-loop iteration), such as a mouse down event, and drains it at the end, so your code normally does not have to worry about them. There are three cases, though, where you might use your own autorelease pools:

If you are writing a program that is not based on the Application Kit, such as a command-line tool, there is no built-in support for autorelease pools; you must create them yourself.

If you spawn a secondary thread, you must create your own autorelease pool as soon as the thread begins executing; otherwise, you will leak objects. (See “Autorelease Pools and Threads” for details.)

If you write a loop that creates many temporary objects, you may create an autorelease pool inside the loop to dispose of those objects before the next iteration. This can help reduce the maximum memory footprint of the application.

I’d say don’t bother, just allocate any objects as required, then release them before returning from the method.

Also, see this post.