为了遍历数组，我们应该使用size_t还是ptrdiff_t? [英] For iterating though an array should we be using size_t or ptrdiff_t?

问题描述

在此博客中Andrey Karpov题为关于size_t和ptrdiff_t" 他展示了一个例子，

In this blog entry by Andrey Karpov entitled, "About size_t and ptrdiff_t" he shows an example,

for (ptrdiff_t i = 0; i < n; i++)
  a[i] = 0;

但是，我不确定这是否正确，看来应该是

However, I'm not sure if that's right, it seems that should be

for (size_t i = 0; i < n; i++)
  a[i] = 0;

这正确吗?

我知道我们也应该使用memset之类的东西，但让我们完全避免这种情况.我只问类型

I know we should also likely be using something like memset, but let's avoid that entirely. I'm only asking about the type

推荐答案

在

In a blog post, I argue that you should always refrain from allocating memory blocks larger than PTRDIFF_MAX(*), because doing so will make compilers such as Clang and GCC generate nonsensical code even if you do not subtract pointers to that block in a way that causes the result to overflow.

(*)即使malloc成功传递给它，它的值也大于PTRDIFF_MAX.问题的症结在于，GCC和Clang仅生成与这样的malloc链接时正确运行的代码，而Glibc提供的malloc函数没有实现此限制.

(*) Even if malloc succeeds when you pass it a value larger than PTRDIFF_MAX. The crux of the problem is that GCC and Clang only generate code that behaves correctly when linked with such a malloc, but Glibc provides a malloc function that does not implement this limitation.

如果您遵循该约束(我鼓励您这样做:这是博客文章的内容)，那么两种类型都同样正确.

If you follow that constraint (which I encourage you to: that's the message of the blog post), then both types are equally correct.

这就是说，由于仅需要表示正偏移量，因此size_t是您示例中的自然选择.

This said, since only positive offsets need to be represented, size_t would be the natural choice in your example.

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