C++ cli call managed code from unmanaged code

Question

Im trying to learn how to write mixed code in CLI/C++.

clrHookLib.h

#pragma once
#pragma managed
using namespace System;
namespace clrHookLib {

    ref class MyClass
    {
        // TODO: Add your methods for this class here.
        public:
        static int sum(int a, int b);
    };

}

clrHookLib.cpp

#include "stdafx.h"
#include "clrHookLib.h"

int clrHookLib::MyClass::sum(int a, int b)
{
    return a + b;
}

main.cpp

#include "clrHookLib.h"
#include "Stdafx.h"

#pragma unmanaged

BOOL WINAPI DllMain(
    _In_ HINSTANCE  hInstance,
    _In_ DWORD      Reason,
    _In_ LPVOID     Reserved)
{
    switch (Reason)
    {
        case DLL_PROCESS_ATTACH:
        {
            int b = clrHookLib::MyClass::sum(1, 2);
            std::string str = std::to_string(b);
            MessageBoxA(0, str.c_str, "result from managed code!!", MB_OK);
            break;
        }
    }
}

While compilling Visual studio shows me an errors:

Error   2   error C2653: 'clrHookLib' : is not a class or namespace name    C:\Users\*\Documents\Visual Studio 2013\Projects\clrHookLib\clrHookLib\Main.cpp 15  1   clrHookLib
Error   3   error C3861: 'sum': identifier not found    C:\Users\*\Documents\Visual Studio 2013\Projects\clrHookLib\clrHookLib\Main.cpp 15  1   clrHookLib
Error   4   error C3867: 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>::c_str': function call missing argument list; use '&std::basic_string<char,std::char_traits<char>,std::allocator<char>>::c_str' to create a pointer to member C:\Users\*\Documents\Visual Studio 2013\Projects\clrHookLib\clrHookLib\Main.cpp 17  1   clrHookLib

The question is why compiller cant find clrHookLib namespace? What im doing wrong?

Thanks.

[ADDED]

I have found some code at microsoft site. May be it will be useful for someone:

// initializing_mixed_assemblies.cpp
// compile with: /clr /LD 
#pragma once
#include <stdio.h>
#include <windows.h>
struct __declspec(dllexport) A {
   A() {
      System::Console::WriteLine("Module ctor initializing based on global instance of class.\n");
   }

   void Test() {
      printf_s("Test called so linker does not throw away unused object.\n");
   }
};

#pragma unmanaged
// Global instance of object
A obj;

extern "C"
BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved) {
   // Remove all managed code from here and put it in constructor of A.
   return true;
}

I think, no comment

You are struggling with basic language syntax. But you are most of all digging yourself a deep hole you can never get out of by trying to run managed code in DllMain(). That's forbidden, that will trigger the infamous loader lock. Find a decent tutorial or book to avoid making all these mistakes. — Hans Passant
– Hans Passant, Commented Dec 19, 2013 at 14:29
Thanks for the answer. But can i call external managed dll to call it from my unmanaged DllMain? — Alexey Kulikov
– Alexey Kulikov, Commented Dec 19, 2013 at 15:30
Im found info: msdn.microsoft.com/ru-ru/library/ms173266.aspx — Alexey Kulikov
– Alexey Kulikov, Commented Dec 19, 2013 at 15:39

Matt Smith · Accepted Answer · 2013-12-19 14:24:06Z

1

You used #pragma unmanaged

So, you can't use any managed code there.

answered Dec 19, 2013 at 14:24

Matt Smith

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