[英]What's the difference between the WIN32 and _WIN32 defines in C++

I know that WIN32 is obviously to denote win32 compilation but what is the need for _WIN32?


3 个解决方案



WIN32 is a name that you could use and even define in your own code and so might clash with Microsoft's usage. _WIN32 is a name that is reserved for the implementor (in this case Microsoft) because it begins with an underscore and an uppercase letter - you are not allowed to define reserved names in your own code, so there can be no clash.




To elaborate (Neil Butterworth and blue.tuxedo have already given the correct answer):


  • WIN32 is defined by the SDK or the build environment, so it does not use the implementation reserved namespace
  • WIN32是由SDK或構建環境定義的,因此它不使用實現保留的名稱空間
  • _WIN32 is defined by the compiler so it uses the underscore to place it in the implementation-reserved namespace
  • _WIN32是由編譯器定義的,因此它使用下划線將其放在實現保留的名稱空間中

You'll find a similar set of dual defines with nearly identical names and similar uses such as _UNICODE/UNICODE, _DEBUG/DEBUG, or maybe _DLL/DLL (I think that only the UNICODE ones get much of any use in their different versions). Though sometimes in these cases (like _UNICODE), instead of the underscore version being defined by the compiler, they are used to control what the CRT headers do:


  • _UNICODE tells the CRT headers that CRT names which can be either Unicode or ANSI (such as _tcslen() should map to the wide character variant (wcslen())
  • _UNICODE告訴CRT頭文件,可以是Unicode或ANSI(比如_tcslen())的CRT名稱應該映射到寬字符變體(wcslen())
  • UNICODE does something similar for the SDK (maps Win32 APIs to their "W" variants)
  • UNICODE對SDK也有類似的功能(將Win32 api映射到它們的“W”變體)

Essentially the versions with the underscore are controlled by or used by the compiler team, the versions without the underscore are controlled/used by teams outside of the compiler. Of course, there's probably going to be a lot overlap due to compatibility with past versions and just general mistakes by one team or the other.


I find it confusing as hell - and find that they are used nearly interchangeably in user code (usually, when you see one defined, you'll see the other defined in the same place, because if you need one you need the other). Personally, I think that you should use the versions without the underscore (unless you're writing the compiler's runtime) and make sure they both get defined (whether via hearers or compiler switches as appropriate) when you're defining one.


Note that the SDK will define _WIN32 when building for the Mac because the compiler doesn't, kind of overstepping it's bounds. I'm not sure what projects use a Win32 API an a compiler targeting the Mac - maybe some version of Office for the Max or something.

注意,在為Mac構建時,SDK將定義_WIN32,因為編譯器不會,有點超出它的界限。我不確定哪個項目使用Win32 API,哪個編譯器針對的是Mac——也許是某個版本的Office for the Max什么的。



WIN32 is a user-defined flag which may be required by some headers. _WIN32 is automatically defined by the visual C/C++ compiler. Since it begins with an _ followed by a capital character, it is reserved by the implementation (meaning the C/C++ toolchain provider).

WIN32是一個用戶定義的標志,有些標題可能需要它。_WIN32是由visual C/ c++編譯器自動定義的。因為它以_開頭,后面跟着一個大寫字符,所以由實現保留(意味着C/ c++工具鏈提供者)。

I prefer to use (read) _WIN32, seems safer to me.

我更喜歡使用(read) _WIN32,對我來說更安全。



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