How to remove NSString Related Memory Leaks? - objective-c

Question

in my application this method shows memory leak how do i remove leak?
-(void)getOneQuestion:(int)flashcardId categoryID:(int)categoryId
{
flashCardText = [[NSString alloc] init];
flashCardAnswer=[[NSString alloc] init];
//NSLog(#"%s %d %s", __FILE__, __LINE__, __PRETTY_FUNCTION__, __FUNCTION__);
sqlite3 *MyDatabase;
sqlite3_stmt *CompiledStatement=nil;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *MyDatabasePath = [documentsDirectory stringByAppendingString:#"/flashCardDatabase.sqlite"];
if(sqlite3_open([MyDatabasePath UTF8String],&MyDatabase) == SQLITE_OK)
{
sqlite3_prepare_v2(MyDatabase, "select flashCardText,flashCardAnswer,flashCardTotalOption from flashcardquestionInfo where flashCardId=? and categoryId=?", -1, &CompiledStatement, NULL);
sqlite3_bind_int(CompiledStatement, 1, flashcardId);
sqlite3_bind_int(CompiledStatement, 2, categoryId);
while(sqlite3_step(CompiledStatement) == SQLITE_ROW)
{
self.flashCardText = [NSString stringWithUTF8String:(char *)sqlite3_column_text(CompiledStatement,0)];
self.flashCardAnswer= [NSString stringWithUTF8String:(char *)sqlite3_column_text(CompiledStatement,1)];
flashCardTotalOption=[[NSNumber numberWithInt:sqlite3_column_int(CompiledStatement,2)] intValue];
}
sqlite3_reset(CompiledStatement);
sqlite3_finalize(CompiledStatement);
sqlite3_close(MyDatabase);
}
}
this method also shows leaks.....what's wrong with this method?
-(void)getMultipleChoiceAnswer:(int)flashCardId
{
if(optionsList!=nil)
[optionsList removeAllObjects];
else
optionsList = [[NSMutableArray alloc] init];
sqlite3 *MyDatabase;
sqlite3_stmt *CompiledStatement=nil;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *MyDatabasePath = [documentsDirectory stringByAppendingString:#"/flashCardDatabase.sqlite"];
if(sqlite3_open([MyDatabasePath UTF8String],&MyDatabase) == SQLITE_OK)
{
sqlite3_prepare_v2(MyDatabase,"select OptionText from flashCardMultipleAnswer where flashCardId=?", -1, &CompiledStatement, NULL);
sqlite3_bind_int(CompiledStatement, 1, flashCardId);
while(sqlite3_step(CompiledStatement) == SQLITE_ROW)
{
[optionsList addObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(CompiledStatement,0)]];
}
sqlite3_reset(CompiledStatement);
sqlite3_finalize(CompiledStatement);
sqlite3_close(MyDatabase);
}
}
alt text http://www.freeimagehosting.net/uploads/5b8120982c.png

Answer 1

You don't actually use the objects you initialise at the top of the function:
flashCardText = [[NSString alloc] init];
flashCardAnswer=[[NSString alloc] init];
as you replace those objects with others later on:
self.flashCardText = [NSString stringWithUTF8String:(char *)sqlite3_column_text(CompiledStatement,0)];
self.flashCardAnswer= [NSString stringWithUTF8String:(char *)sqlite3_column_text(CompiledStatement,1)];
So those would seem to be the objects that are leaking.

Answer 2

[[NSString alloc] init] is completely pointless. It will return exactly equivalent of #"", except wiht more work. Its unlikely to leak, since the system will almost certainly return you a fixed constant empty string, releasing the [NSString alloc] in the init routine. But it is pointless and useless and bad code.
Other than that, your code looks OK. The second method might be considered to "leak" optionsList, simply because it creates it and it is never released, but its only created once so it should be fine.
Try running your program and doing the leak detection, then breaking in the debugger and using
po 0x4b2720 (replace with the address of the leaked objects)
to see what string is actually leaking.
Remember that Leaks can give false positives, especially if anything is cached.

Answer 3

[[NSString alloc] init]; is a useless phrase. Removing the two first lines would get rid of the leak.
EDIT: Note, too, that the two strings you pull from the database will vanish as soon as the autoreleasepool is drained, unless they are retained.
Redit: Concerning the second method; I cannot see any obvious leaks. NSCFStrings are created a lot, and often stick around. That doesn't mean they actually are leaks. From what I can see, everything in that method is either autoreleased or persistent.

Answer 4

-1/2
#"" is equivalent to [[[NSString alloc] init] autorelease];
[[NSString alloc] init] will leak.
Remember the rule: init/retain should be balanced by autorelease/release.