来自[NSArray count]的常量错误是无符号的 [英] Constant bugs from [NSArray count] being unsigned

问题描述

由于没有注意到[NSArray count] unsigned 的后果，我一遍又一遍地制造错误。今天的例子相对不寻常：

I'm creating bugs over and over by failing to notice the consequences of [NSArray count] being unsigned. Today's example is relatively unusual:

for (int i = -1; i < [myArray count]; i++) {

这个循环永远不会执行！你需要（int）[myArray count] 。我通常的错误是：

This loop never executes! You need (int)[myArray count]. My usual mistake is:

for (int i = 0; i < [myArray count] - 1; i++) {

如果数组为空，则此循环基本上永远执行，因为 [myArray count] -1 溢出 unsigned int 。

If the array is empty, this loop executes basically forever because [myArray count]-1 overflows the unsigned int.

我尽可能使用快速枚举，但是在这个项目中我经常需要在处理对象时在索引 i-1 和 i + 1 中引用对象我并且它似乎不适合它。还有其他任何避免这些错误的技巧，除了不那么无能之外吗？

I do use fast enumeration where possible, but in this project I very often need to refer the objects at indexes i-1 and i+1 while processing object i and it doesn't seem to lend itself to that. Any other tips for avoiding these bugs, other than just being less incompetent?

推荐答案

首先，有一个警告你可以打开拿起这些问题。我认为这是符号比较，命令行标志是 -Wsign-compare 。

Firstly, there's a warning you can turn on to pick up these issues. I think it's "sign comparison", the command line flag is -Wsign-compare.

如果你想迭代一个数组的元素但是你需要索引，那么最好的方式（在我看来）是 - enumerateObjectsUsingBlock：

If you want to iterate over the elements of an array but you need the index, the neatest way (in my opinion) is -enumerateObjectsUsingBlock:

[myArray enumerateObjectsUsingBlock: ^(id obj, NSUInteger idx, BOOL *stop) 
{
    NSlog(@"Object at index %lu is %@", (unsigned long) idx, obj);
    if (idx > 0)
    {
        NSlog(@"Previous object is %@", [myArray objectAtIndex: idx - 1]);
    }
    if (idx + 1 < [myArray count])
    {
        NSlog(@"Next object is %@", [myArray objectAtIndex: idx + 1]);
    }
}];

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