测试无效的 Windows 句柄：我应该与“NULL”、“0”甚至“nullptr”进行比较吗？
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Testing for an invalid windows handle: should I compare with 'NULL', '0' or even 'nullptr'?
提问by Coder_Dan
I'm coming from a background whereby pointers should generally be compared with 'NULL' and integers with '0'.
我来自一个背景，即通常应该将指针与“NULL”和整数与“0”进行比较。
Since I didn't perceive Windows handles to be 'pointers' in the pure sense (being 'handles'), I'd got into the habit of comparing them with 0 rather than 'NULL'.
由于我没有将 Windows 句柄视为纯粹意义上的“指针”（即“句柄”），因此我养成了将它们与 0 而不是“NULL”进行比较的习惯。
Clearly they're implemented internally as pointers nowadays, but I personally consider that to be merely for acquiring some type-safety rather than because they are intrinsically pointers.
显然，它们现在是作为指针在内部实现的，但我个人认为这仅仅是为了获得某种类型安全性，而不是因为它们本质上是指针。
Anyway, I just noticed that the help for CreateIC which returns an HDC states that if the function fails then it returns 'NULL'.
无论如何，我只是注意到返回 HDC 的 CreateIC 的帮助指出，如果函数失败，则返回“NULL”。
Now I'm confused - and am wondering what other people reckon - is it more correct to consider a Windows handle to be a pointer (and therefore check it against 'NULL' or 'nullptr' for modern compilers) or should it be considered to be an integer?
现在我很困惑 - 我想知道其他人的看法 - 将 Windows 句柄视为指针是否更正确（因此对于现代编译器，将其与“NULL”或“nullptr”进行检查）还是应该考虑是整数？
采纳答案by MSalters
Compare it against the documented error return value. That means that you should compare it against INVALID_HANDLE, 0, -1, non-zero, or <=32(I'm not kidding with the last one, see ShellExecute).
将其与记录的错误返回值进行比较。这意味着您应该将它与INVALID_HANDLE、0、-1、非零或<=32（我不是在和最后一个开玩笑，请参阅 ShellExecute）进行比较。
回答by Frerich Raabe
To answer your question: the HANDLEtype is declared in winnt.h as
回答您的问题：该HANDLE类型在 winnt.h 中声明为
typedef PVOID HANDLE;
Hence, technically it is a pointer.
因此，从技术上讲，它是一个指针。
However, I would just use whatever is documented; if the documentation states that NULLis returned, I use exactly that unless evidence shows that the documentation is incorrect.
但是，我只会使用记录在案的任何内容；如果文档说明NULL已返回，我将完全使用该文档，除非有证据表明文档不正确。
I don't even think about pointers vs. integers. NULLis just an opaque value (in this situation) and HANDLEis an opaque type to me and I don't bother looking up what it is #define'd to.
我什至不考虑指针与整数。NULL只是一个不透明的值（在这种情况下）并且HANDLE对我来说是一个不透明的类型，我不费心去查找它是什么#define。
回答by sje397
I think INVALID_HANDLE_VALUEis usually the proper 'invalid' value for windows handles...and that evaluates to -1.
我认为INVALID_HANDLE_VALUE通常是 Windows 句柄的正确“无效”值......并且评估为-1.
