How to implement SetFileSaveFunction callback function?

Question

I develop add-on for MicroStation using CONNECT Edition application with C++. 
 Using Microstation10.15 update SDK 
 I would like to get Save event when save triggered. 
 extern "C" DLLEXPORT void MdlMain(int argc, WCharCP argv[]) { SystemCallback::SetFileSaveFunction(OnFileSave); return; } 
 void OnFileSave(DgnPlatform::ProcessChangesWhen when, DgnPlatform::DgnFileChanges changesFlag, DgnPlatform::DgnSaveReason reason, double timestamp, DgnFileP pFile) { WString Filename = pFile->GetFileName(); if (reason == DgnPlatform::DgnSaveReason::UserInitiated) { 
 /// do operations } 
 } 
 OnFileSave function is never called. 
 How can I make this callback functionality working?

Robert Hook · Answer

Rajesh Varatharajan , 
 Rajesh Varatharajan said: After moving OnFileSave() before to MdlMain it works. 
 You don't need to move your functions around in your code to ensure proper/strict compiler resolution, you need to Declare your Functions. 
 In Visual Studio, simply: 
 
 Click on a function name not declared/compiling 
 Ctrl + . (Quick Actions) 
 Choose: Create Declaration / Definition

Lastly/Ideally you take all needed declarations and store those in a single project header file (prefaced with: #pragma once) that you can then cleanly include in all your project(s) source code files improving code maintenance and a clean implementation. 
 HTH, Bob