Question

I know the purpose and usage of include guards around the .h file in C++

  #ifndef FILENAME_H
  #define FILENAME_H
  #endif

However, I am trying to understand the usage for #ifdef TEST_FILENAME in the test stub or around the main() method used to test run the class.

  #ifdef TEST_FILENAME
   void main()
   {
      /////////////////
   }
  #endif

Answer 1

It’s probably so that you can have a conditional main function run.

If you’re testing, you’ll want a test routine to run, if not you’ll probably want to execute your actual main function. This allows you define the macro during compile-time so that the preprocessor can give you the right main to build.