NSUInteger是否在反向循环中感到困惑? [英] NSUInteger in reversed loop confusion?

问题描述

我想知道是否有人可以解释一些问题，所以我设置了一个循环，希望从10倒数到0:

I wonder if someone can explain something, I setup a loop where I wanted to count backwards from 10 to 0 :

for(NSUInteger index = 10; index >= 0; index--) {
    NSLog(@"INDEX: %ld", (long)index);
}

此循环永远运行，它不会在0处停止，但会一直变为负数.当我注意到这一点时，我将代码更改为:

This loop runs forever, it does not stop at 0, but keeps going into negative numbers. When I noticed this I changed my code to :

for(NSInteger index = 10; index >= 0; index--) {
    NSLog(@"INDEX: %ld", (long)index);
}

上面的方法工作正常，但我很好奇，为什么第一个示例不起作用，因为生成的数字都是无符号整数?

The above works fine, but I am curious, why the first example does not work as the numbers generated are all unsigned integers?

推荐答案

无符号类型不能保持负数".在index = 0的迭代之后，index--变为0xFFFFFFFF，仍然大于零.容易犯的错误，我自己做了.

An unsigned type can't "keep going into negative numbers". After the iteration when index = 0, index-- becomes 0xFFFFFFFF, which is still more than zero. Easy mistake to make, I've done it myself.

静态分析器实际上会警告您(条件索引> = 0始终为真"或类似的东西.)我强烈建议将其设置为在调试版本中自动运行.

The static analyzer will actually warn you about this ("Condition index >= 0 is always true" or such like.) I highly recommend setting it to run automatically on debug builds.

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