Newbie leaks that I don't quite understand

Question

After fixing other leaks that Instruments was indicating, I find myself in need for help to find my leaches in the following code:

-(void) readHistoryFromDatabase { sqlite3 *database;

NSMutableArray *days = [[NSMutableArray alloc] init];

NSInteger currentMonth;

int noMonths = 0;

int historyCount = 0;

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];

[dateFormat setDateFormat:@"yyyy-MM-dd"];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"database.sqlite"];

if(sqlite3_open([filePath UTF8String], &database) == SQLITE_OK) { 
    const char *sqlStatement = "select data, rata, var, strftime('%m', data) month from rates where id=?"; 
    sqlite3_stmt *compiledStatement; 

    if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
        sqlite3_bind_int(compiledStatement, 1, id);
        while(sqlite3_step(compiledStatement) == SQLITE_ROW) {
            NSDate   *data      = [dateFormat dateFromString:[NSString stringWithUTF8String:(char *) sqlite3_column_text(compiledStatement, 0)]];
            NSString *rata      = [NSString stringWithUTF8String:(char *) sqlite3_column_text(compiledStatement, 1)];
            NSString *var       = [NSString stringWithUTF8String:(char *) sqlite3_column_text(compiledStatement, 2)];
            NSInteger month     = sqlite3_column_int(compiledStatement, 3);

            if ((currentMonth != month) && (historyCount > 0)) {
                [self.rate setValue:[days copy] forKey:[NSString stringWithFormat:@"%d", noMonths]];

                noMonths++;
                [days removeAllObjects];
                currentMonth = month;
            } else if (historyCount == 0) {
                currentMonth = month;
            }

            CHis *new = [[CHis alloc] init]; 
            new.rata  = rata;
            new.var   = variatie;
            new.month = month;
            new.data  = data;
            historyCount++;
            [days addObject:new];
            [new release];
        }
        if ([days count] > 0) {
            [self.rate setValue:[days copy] forKey:[NSString stringWithFormat:@"%d", noMonths]];
        }
    }
    sqlite3_finalize(compiledStatement);
}
[dateFormat release];
[days release];
sqlite3_close(database);

}

self.rate is defined this way:

@property (nonatomic, retain) NSMutableDictionary *rate;

and in viewDidLoad:

self.rate = [[NSMutableDictionary alloc] init];

Basically this part of code reads from a database some rates. Based on the month it will put in a NSDictionary a pair of month and an Array with the rates.

I don't understand where is the leak. I know that perhaps it is something very easy but I am searching for 2 days now for a solution .....

Answer 1

[[NSMutableDictionary alloc] init] returns an object with retain count 1. Then you assign it to self.rate which increases the retain count (will then be 2). If you assign something else to self.rate , the previous object's retain count will drop back to 1. But it won't reach 0.

There are three solutions:

// OK
self.rate = [[[NSMutableDictionary alloc] init] autorelease];

// Better, has the same effect as statement above
self.rate = [NSMutableDictionary dictionary];

// Clumsy, but works
NSMutableDictionary *tmp = [[NSMutableDictionary alloc] init];
self.rate = tmp;
[tmp release];

Remember, everytime you call alloc/init or copy , you get an object that you own. This means you are immediately responsible for calling release on them. Almost every other method will/should return an object that you do not need to call release on, except if you called retained on it to "claim ownership".

Answer 2

在仪器中，您可以查看泄漏的来源，按扩展的详细信息按钮并选择泄漏，然后您将看到泄漏的来源，方法和文件。