testing new operator fail

Question

I've created a class in which there's some new operator in the constructor. I've created the guard into the constructor to manage new operator failing, but now I want to test it.

As example, I've a constructor that is like this:

Function::Function()
{
  try
  {
    m_pxArgument = new Argument();
  }
  catch(std::bad_alloc)
  {
    throw MemoryException();
  }
}

Is it possible to create a test in which I can tell the new operator to fail, to test my catch code?

Answer 1

If Argument is your class/struct - then define operator new in this class just for UT purposes.

class Argument {
//...
#ifdef UNIT_TEST
   static bool& failNew() { static bool failNew = false; return failNew; }
   void* operator new(size_t size)
   {
       if (!failNew())
         return ::operator new (size);
       failNew() = false;       
       throw std::bad_alloc("Argument");
   }
#endif
};

Just set Argument::failNew() = true; every time you need to fail its allocation.