Can a dll file be initialized - A Dll constructor - c++

Question

I am currently importing a function out of my dll in the following way in a C# application.
[DllImport("C:\\File.dll")]
public static extern int SomeMethod(int A);
My dll file is written in C++. This method is also defined in the .def file of the dll.
Currently whenever this method is called in the first ever attempt a couple of other methods are called , these methods set up the grounds for this method. However these methods only need to be called once. These methods are never called again/ I wanted to know is there a way to call a group of methods (initializers) as soon as a dll file is loaded. Is there anything as a dll constructor ?
I have something like this in my dllmain.cpp could entering something in there accomplish this task
// dllmain.cpp : Defines the entry point for the DLL application.
#include "stdafx.h"
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}

Answer 1

DllMain is the closest to a DLL "constructor" (and the correct place to do initialization is in the case label for DLL_PROCESS_ATTACH). However a more realistic constructor would be that of a COM class instantiated by the C# code. In that case the constructor would be called for every instance of the class that you create (just like for a C# class). Create an ATL project in Visual C++ and it will generate code like this for you:
class ATL_NO_VTABLE CMyClass :
public CComObjectRootEx<CComSingleThreadModel>,
public CComCoClass<CMyClass, &CLSID_MyClass>,
public IMyClass
{
public:
CMyClass()
{
}
DECLARE_REGISTRY_RESOURCEID(IDR_MYCLASS1)
BEGIN_COM_MAP(CMyClass)
COM_INTERFACE_ENTRY(IMyClass)
END_COM_MAP()
DECLARE_PROTECT_FINAL_CONSTRUCT()
HRESULT FinalConstruct()
{
return S_OK;
}
void FinalRelease()
{
}
...
In the CMyClass constructor or in the FinalConstruct method you can perform the initialization code for the object. Also add your SomeMethod method to this class (and to the IDL interface in the IDL file).
Then you would use that class in C# like this:
MyClass mc = new MyClass(); // CMyClass::CMyClass and CMyClass::FinalConstruct are called in C++
mc.SomeMethod(); // CMyClass::SomeMethod is called in C++