C 中有没有标准函数可以返回数组的长度? [英] Is there a standard function in C that would return the length of an array?

问题描述

C 中有没有标准函数可以返回数组的长度?

Is there a standard function in C that would return the length of an array?

推荐答案

通常其他答案中描述的技术被封装在一个宏中，以使其更容易理解.类似的东西:

Often the technique described in other answers is encapsulated in a macro to make it easier on the eyes. Something like:

#define COUNT_OF( arr) (sizeof(arr)/sizeof(0[arr]))

请注意，上面的宏使用了一个小技巧，将数组名称放入索引运算符 ('[]') 而不是 0 - 这是在如果宏在 C++ 代码中被错误地用于重载 operator[]() 的项目.编译器会抱怨而不是给出一个糟糕的结果.

Note that the macro above uses a small trick of putting the array name in the index operator ('[]') instead of the 0 - this is done in case the macro is mistakenly used in C++ code with an item that overloads operator[](). The compiler will complain instead of giving a bad result.

但是，还要注意，如果您碰巧传递的是指针而不是数组，宏会默默地给出一个糟糕的结果——这是使用这种技术的主要问题之一.

However, also note that if you happen to pass a pointer instead of an array, the macro will silently give a bad result - this is one of the major problems with using this technique.

我最近开始使用从 Google Chromium 代码库中窃取的更复杂的版本:

I have recently started to use a more complex version that I stole from Google Chromium's codebase:

#define COUNT_OF(x) ((sizeof(x)/sizeof(0[x])) / ((size_t)(!(sizeof(x) % sizeof(0[x])))))

在这个版本中，如果一个指针被错误地作为参数传递，编译器会在某些情况下抱怨——特别是如果指针的大小不能被指针指向的对象的大小整除.在这种情况下，除以零将导致编译器出错.实际上，我使用过的至少一个编译器会给出警告而不是错误 - 我不确定它会为除以零的表达式生成什么.

In this version if a pointer is mistakenly passed as the argument, the compiler will complain in some cases - specifically if the pointer's size isn't evenly divisible by the size of the object the pointer points to. In that situation a divide-by-zero will cause the compiler to error out. Actually at least one compiler I've used gives a warning instead of an error - I'm not sure what it generates for the expression that has a divide by zero in it.

该宏不会关闭错误使用它的门，但它与我在直 C 中见过的一样接近.

That macro doesn't close the door on using it erroneously, but it comes as close as I've ever seen in straight C.

如果您在使用 C++ 时想要更安全的解决方案，请查看 不使用宏的编译时间 sizeof_array 描述了微软在 winnt.h 中使用的一种相当复杂的基于模板的方法.

If you want an even safer solution for when you're working in C++, take a look at Compile time sizeof_array without using a macro which describes a rather complex template-based method Microsoft uses in winnt.h.

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