DLL Main on Windows Vs. __attribute__((constructor)) entry points on Linux

Question

Consider code

EXE:

int main ()
{

    printf(\"Executable Main, loading library\\n\");
#ifdef HAVE_WINDOWS
    HMODULE lib = LoadLibrary         


        

Answer 1

There is a way:

StartupCleanup.cpp:

// Redefine the same StartupCleanup class as it is in DllMain.cpp
// Definition of constructor and destructor must stay in DllMain.cpp
// And including here any headers which may define normal static or global constructors/destructors is strictly forbidden!
struct StartupAndCleanup
{
    /**/  StartupAndCleanup();
    /**/ ~StartupAndCleanup();
};

// It ensures this instance is the first to be constructed *BEFORE* any normal static or global constructors calls
// and the last to be destructed *AFTER* all normal destructors calls.
// The key to do so is using #pragma init_seg(lib), but that key applies for all the static and global constructors/destructors in the same .obj file! 
#pragma warning(push)
#pragma warning(disable:4073)
#pragma init_seg(lib)
#pragma warning(pop)

// this function is just to keep linker from discarding startupAndCleanup.obj when linking to an executable or dll
void needStartupAndCleanup()
{
}

static StartupAndCleanup startupAndCleanup;

DllMain.cpp:

...
// Definition of this class should be the same as in StartupAndCleanup.cpp!
struct StartupAndCleanup
{
    /**/  StartupAndCleanup();
    /**/ ~StartupAndCleanup();
};

StartupAndCleanup::StartupAndCleanup()
{
    // Do your initialization here !
}

StartupAndCleanup::~StartupAndCleanup()
{
    // Do your termination here !
}

You DllMain must be just an empty shell and do your usual safe initialization and termination in those constructor and destructor like for Linux.

NOTE: Beware! you cannot create/delete threads inside static or global constructors/destructors if you plan to synchronize them. That's all folks !

EDIT: you also need to call needStartupAndCleanup() in a function you know it is linked, otherwise the object file StartupCleanup.obj will be discarded and those global constructor/destructor as well.