Objective-c array

Question

I am slightly confused as I am using this piece of code;

NSArray *dirContents = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:@"/Volumes/" error:nil];

int arraysize = sizeof dirContents;

to get an array of the contents of the "Volumes" direcoty, however when I output the array size it says that the array has 8 entries when there are only 4 files in that directory? This wouldn't be a problem but since I am using a for loop as soon as I get to;

NSString *volume1 = [dirContents objectAtIndex:4];

(4 being the value in the for loop) the application crashes and refuses to launch?

Thanks for any help

Answer 1

You should use int arraysize = [dirContents count] to get the correct size.

sizeof is a c-style operator that will not work correctly on Objective-C objects.

Answer 2

sizeof does not returns the length of the array but the size your variable occupies in memory. Since dirContents is a pointer it occupies only 8 byte.

To get the length of the array you should use

[dirContents count];

Besides, in arrays, objects are stored with indexes starting from 0. Thus, if your array has only 4 elements, [dirContents objectAtIndex:4] will end in a runtime error, since you are trying to retrieve the element in the fifth position.

Answer 3

sizeof is receiving the size of the pointer. Instead use int arraysize = [dirContents count];

Answer 4

Taking sizeof is not the right way of finding the number of NSArray elements. Use dirContents.count instead.