我有一个混合模式 DLL，其中有一个包含托管和非托管代码的 .cpp 文件。一个简化的重现示例如下所示：
#include "stdafx.h"
#pragma managed // Just for explicitness (doesn't influence results)
#include <msclr\marshal.h>
void Test()
{
System::String^ sName = "";
msclr::interop::marshal_context context;
context.marshal_as<const TCHAR*>(sName);
}
//#pragma unmanaged // uncomment this line to get errors
该代码编译成功，但是如果我取消注释最后一行（#pragma unmanaged），它会产生以下错误：
2> Test.cpp
2>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\msclr\marshal.h(48): error C3280: 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler' : a member-function of a managed type cannot be compiled as an unmanaged function
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2> This diagnostic occurred in the compiler generated function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\msclr\marshal.h(48): error C3642: 'System::Object::Object(void)' : cannot call a function with __clrcall calling convention from native code
2> This diagnostic occurred in the compiler generated function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\msclr\marshal.h(48): error C3175: 'System::Object::Object' : cannot call a method of a managed type from unmanaged function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2> This diagnostic occurred in the compiler generated function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\msclr\marshal.h(48): error C3821: 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)': managed type or function cannot be used in an unmanaged function
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2> This diagnostic occurred in the compiler generated function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\msclr\marshal.h(282): error C3645: 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler' : __clrcall cannot be used on functions compiled to native code
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
2> This diagnostic occurred in the compiler generated function 'msclr::interop::marshal_context::internal_marshaler<_To_Type,_From_Type,_Needs_Context>::internal_marshaler(void)'
2> with
2> [
2> _To_Type=const wchar_t *,
2> _From_Type=System::String ^,
2> _Needs_Context=true
2> ]
我发现我可以通过添加来消除错误#pragma managed在我的 .cpp 文件的末尾。但我还是不明白why发生错误。这种行为的#pragma unmanaged对我来说似乎完全违反直觉。有人可以解释一下吗？
据我所理解：
-
#pragma (un)managed影响代码编译below它。因此，如果它是在 .cpp 文件末尾定义的（下面没有任何内容），则它不应该产生任何效果。
- Also http://msdn.microsoft.com/en-us/library/0adb9zxe.aspxhttp://msdn.microsoft.com/en-us/library/0adb9zxe.aspx http://msdn.microsoft.com/en-us/library/0adb9zxe.aspx says:
实例化模板函数时，模板定义时的编译指示状态决定它是托管的还是非托管的。
