objective-c - Objective-C, Comparison of unsigned expression < 0 is always false, error?

Question

I'm getting the following warning Comparison of unsigned expression < 0 is always false.

I'm not sure how to fix it ?

if(topWindowIndex < 0)

It's defined as...

NSUInteger topWindowIndex = [allWindows count] - 1;

Answer 1

If [allWindows count] - 1 can never be negative, the test (and the code it controls) is unnecessary. If it can be negative, you should declare topWindowIndex as a signed type (int or NSInteger).

A better solution, IMO, is to store the count directly and use that instead:

NSUInteger numWindows = [allWindows count];
...
if (numWindows < 1) ...

Answer 2

这很危险

NSUInteger topWindowIndex = [allWindows count] - 1;

如果[allWindows count]是 0，你会得到一个非常大的数字（废话）作为 topWindowIndex。

Answer 3

上述答案的基本答案：

使用NSInteger代替NSUInteger（无符号）。