C++ Call a function dynamically from a dll

[nullptr_t]

#include <Windows.h>

//replacement for the MessageBoxApi Function:
typedef int (WINAPI* DynamicMessageBoxFunc)(HWND wnd, LPCSTR message, LPCSTR title, UINT icon);

//this is the actual replacement function:
int __stdcall DynamicMessageBox(HWND wnd, LPCSTR message, LPCSTR title, UINT icon)
{
	BOOL FreeResult = 0, RunTimeLinkSuccess = 0; //variables for later use
	HMODULE LibraryHandle = 0; //Here the handle to API module/dll will be stored.
	DynamicMessageBoxFunc DynMsgBox = 0;

	LibraryHandle = LoadLibrary("user32.dll"); //get the handle of our API module
	//by loading it to the current process. MessageBoxA function is defined in user32.dll
	//so it will now be loaded.
	if (LibraryHandle != NULL) //if the library loading was successfull..
	{
		DynMsgBox = (DynamicMessageBoxFunc)GetProcAddress(LibraryHandle,
			"MessageBoxA"); //Get the address of MessageBoxA in user32.dll
		if (RunTimeLinkSuccess = (DynMsgBox != NULL)) //if operation was successful...
		{
			int ReturnValue = DynMsgBox(wnd, message, title, icon); //call messageboxa function
			//from user32.dll
		}
		FreeResult = FreeLibrary(LibraryHandle); //after we called messagebox, unload user32.dll
		//from this process...
		return FreeResult; //routine was successful
	}
	return EXIT_FAILURE; //else, it failed
}

//now let's use it:

int main()
{
	DynamicMessageBox(0, "Hello, this is a test!", "test!", 0);
	return 0;
}