“错误C2653：系统不是类或命名空间名称”在Form头文件中，Visual C ++ [英] "error C2653: System is not a class or a namespace name" in Form header file, Visual C++

问题描述

我关于同一项目的以前的问题：一个和两个。没有必要读它们;只是知道我试图在Visual C ++项目中使用本机C ++ SDK。这比我最初想的要复杂得多，但这个网站关于用托管代码扩展本地C ++项目已经帮助我了很多。

按照最后一个链接的说明，我已经添加了一个窗体到我的本地C + +项目，它已经自动转换为一个CLR项目。只有 MainForm.cpp 和 Interface.cpp （允许本地C ++代码创建和显示MainForm的文件）编译时使用 / clr 标志;其他文件保持原生。

我现在的问题是，Visual Studio似乎不认识任何在 MainForm.h 。因此，在以下行中：

 使用命名空间System; 
 using namespace System :: ComponentModel; 
 using namespace System :: Collections; 
 using namespace System :: Windows :: Forms; 
 using namespace System :: Data; 
 using namespace System :: Drawing; 
  

单词系统 ，根据错误：

 错误C2653：'System'不是类或命名空间名称
  
 
 
它也不能识别这个字符。c $ c> 
 
 
 <  gcnew 和其他应该在CLR中毫不费力地工作。
 
 
 
任何人都可以告诉我我可能做错了什么？我的猜测是，它的东西很小;一些标志我忘了改变，一个缺失的引用或类似的东西，但我只是不能弄清楚它是什么。
解决方案
 p>您在哪里包含 MainForm.h   - 直接和间接？
 
如果包括 MainForm.h 在 Interface.h 中，您可以间接地包括 Interface.h 。这意味着，如果你在任何翻译单元（即* .cpp）中包含 Interface.h ，而不是使用 / clr ，那么编译器当然会抱怨，因为命名空间System 和 gcnew 不是标准的一部分因此，您应该包括 MainForm.h 仅在 Interface.cpp  code>并在 Interface.h 中使用向前声明。
 
My previous questions concerning the same project: one and two. It's not necessary to read them; just know that I am trying to use a native C++ SDK in a Visual C++ project. This is much trickier than I had initially thought, but this website about Extending a native C++ project with managed code has helped me a lot further already.

As per that last link's instructions, I have added a Form to my native C++ project, which has automatically converted the project to a CLR one. Only MainForm.cpp and Interface.cpp (the file that allows native C++ code to create and show a MainForm) are compiled with the /clr flag though; the other files remain native. 

The problem I have now, is that Visual Studio doesn't seem to recognise any of the CLR stuff that's being used in MainForm.h. As such, in the following lines:
using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;
the word System is always underlined in red, with according errors:
error C2653: 'System' is not a class or a namespace name
for each of those lines.

It also does not recognise the word gcnew and other things that should work effortlessly inside CLR.

Can anybody tell me what I might be doing wrong? My guess is that it's something very small; some flag I have forgotten to change, a missing reference or something similar, but I just can't figure out what it is.
解决方案
Where do you include MainForm.h - directly and indirectly?

If you include MainForm.h in Interface.h, you include it indirectly anywhere where you include Interface.h as well. That means, if you then include Interface.h in any translation unit (i.e. *.cpp) that is not compiled with /clr, then the compiler will of course complain about it, because namespace System and gcnew are not part of standard C++.

Therefore you should include MainForm.h only in Interface.cpp and use forward declarations in Interface.h.

                        
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