有没有在C标准函数将返回数组的长度？ [英] Is there a standard function in C that would return the length of an array?

问题描述

有没有在C标准函数将返回数组的长度？

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

推荐答案

通常在其他的答案中描述的技术被封装在一个宏，使其对眼睛更容易。是这样的：

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，上面的宏使用把数组名索引运算符（ [] '）而不是 0的小窍门 - 这是在做的情况下宏在C code错误地使用了与重载一个项目运算符[]（）。编译器会抱怨，而不是让一个坏的结果。

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.

不过，也请注意，如果你碰巧传递一个指针，而不是一个数组，宏会悄悄地给一个坏的结果 - 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.

我最近开始使用更复杂的版本，我从谷歌Chromium的codeBase的偷了：

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，如果一个指针作为参数错误地传递，编译器会抱怨在某些情况下 - 尤其如果指针的大小不是由对象的大小的指针指向整除。在这种情况下除以零会导致编译器错误的。其实至少有一个编译器，我使用发出警告，而不是一个错误 - 我不知道它会产生对具有在其零鸿沟前pression。

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.

这是宏不结束对错误地使用它的门，但正如我在传统的C见过它作为密切。

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

如果你想，当你在C ++中工作的一个更安全的解决方案，看看<一个href=\"http://stackoverflow.com/questions/1500363/compile-time-sizeofarray-without-using-a-macro/1500917#1500917\">http://stackoverflow.com/questions/1500363/compile-time-sizeofarray-without-using-a-macro/1500917#1500917它描述了 WINNT.H 一个相当复杂的基于模板的方法，微软使用。

If you want an even safer solution for when you're working in C++, take a look at http://stackoverflow.com/questions/1500363/compile-time-sizeofarray-without-using-a-macro/1500917#1500917 which describes a rather complex template-based method Microsoft uses in winnt.h.

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