问题描述
我正在尝试使用P/Invoke从C#调用非托管C ++ DLL中的函数. C ++ DLL使用CString作为函数参数并返回，例如
I'm trying to use P/Invoke to call functions in an unmanaged C++ DLL from C#. The C++ DLL uses CString's as function parameters and returns, such as
CString AFX_EXT_API GetUserName(CString& userID)
不幸的是，C ++是旧代码，我无法更改为使用更通用的LPSTR(甚至是char *).
Unfortunately, the C++ is legacy code that I cannot change to use the more universal LPSTR (or even char *).
是否有任何方法可以将CString编组为.NET兼容对象?还是以某种方式装饰.NET char[]以封送至CString?
Is there any way to marshal the CString into a .NET compatible object? Or somehow decorate a .NET char[] to be marshaled to a CString?
推荐答案
您无法在托管代码中创建CString.因此，显然，在托管代码和本机代码之间需要一个额外的层.
You can't create a CString in managed code. So clearly you need an extra layer between the managed code and the native code.
这为您提供了一个制作介于两者之间的C ++/CLI DLL的机会.您可以从托管程序集中调用此代码，而无需P/invoke.从C ++/CLI中间层，您可以创建CString.
This gives you an opportunity to make a C++/CLI DLL which sits between. You can call this code from your managed assembly without needing P/invoke. And from the C++/CLI middle layer you can create a CString.
但是，有一个警告.您必须使用与本地DLL相同的C ++运行时.这可能是可行的，但很有可能会成为绊脚石.例如，如果DLL是用MSVC6编写的，那么您也将需要用MSVC6构建中间层，这将排除C ++/CLI.在这种情况下，请返回P/invoke和char*.
However, there is one caveat. You must be using the same C++ runtime as the native DLL. This may be possible but it is quite likely that it will be a stumbling block. For example if the DLL was written with MSVC6 then you will need to build your intermediate layer with MSVC6 too and that rules out C++/CLI. Back to P/invoke and char* in that case.
我要强调的是，基于CString导出DLL接口是一种糟糕的做法，我会寻找DLL的替代方案.
I would stress that it is terrible practice to export a DLL interface based on CString and I'd be looking for alternatives to the DLL.
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