Correct primitive array size

Question

I'm trying to use a lighter primitive array, because storing hundreds of thousands NSNumbers in a NSMutableDictionary is causing like 40-50MB memory consumption..

This is my code:

NSUInteger highestModelID = [self.externalDB intForQuery:@"SELECT `id` FROM `models` ORDER BY `id` DESC"];

CGFloat modelsPricesForCustomer[highestModelID];
memset(modelsPricesForCustomer, 0, highestModelID*sizeof(NSUInteger));

NSLog(@"%i", highestModelID);
NSLog(@"%lu", (sizeof modelsPricesForCustomer));

highestModelID is 34078, yet the size says it's 136312. Do I allocate it wrong or read it wrong?

Answer 1

highestModelID is the number of elements in modelsPricesForCustomer, not its size. sizeof, on the other hand, returns the size of the array in bytes, i.e. highestModelID*sizeof(CGFloat)

Since sizeof(CGFloat) on your system is 4, the results are correct:

34078 * 4 = 136312

Note:

memset(modelsPricesForCustomer, 0, highestModelID*sizeof(NSUInteger));
//                                                       ^^^^^^^^^^

should be

memset(modelsPricesForCustomer, 0, highestModelID*sizeof(CGFloat));
//                                                       ^^^^^^^

to avoid clearing part of memory or going past the end of allocated buffer when sizeof(NSUInteger) != sizeof(CGFloat)