why when you initialize array using initWithObjects the last item is "nil"? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

NSArray creation with variable argument lists in Objective-C

th开发者_StackOverflow中文版at's it actually the question is very simple. Xcode suggests that the last item is "nil" and I was wondering why.

array1 = [[NSArray alloc] initWithObjects: @"one", @"two", @"three", @"four", nil];

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A null-termination (nil) character is used to determine the length of an array. Failure to properly terminate an array can result in buffer overflows and other undefined behavior.

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Aside from redirecting to the docs about NSArray initWithObjects, it is worth noting that in general, with variadic functions (i.e. functions that take a variable number of arguments), either you specify the number of arguments upfront, or you terminate the argument list in some way. Nil is a good way of terminating the argument list and is the approach taken with initWithObjects.