Question

One can remove all calls to printf() using #define printf. What if I have a lot of debug prints like std::cout << x << endl; ? How can I quickly switch off cout << statements in a single file using preprocessor?

Answer 1

NullStream can be a good solution if you are looking for something quick that removes debug statements. However I would recommend creating your own class for debugging, that can be expanded as needed when more debug functionality is required:

class MyDebug
{
    std::ostream & stream;
  public:
    MyDebug(std::ostream & s) : stream(s) {}
#ifdef NDEBUG
    template<typename T>
    MyDebug & operator<<(T& item)
    {
      stream << item;
      return *this;
    }
#else
    template<typename T>
    MyDebug & operator<<(T&)
    {
      return *this;
    }
#endif
};

This is a simple setup that can do what you want initially, plus it has the added benefit of letting you add functionality such as debug levels etc..

Update:
Now since manipulators are implemented as functions, if you want to accept manipulators as well (endl) you can add:

MyDebug & operator<<(std::ostream & (*pf)(std::ostream&))
{
  stream << pf;
  return *this;
}

And for all manipulator types (So that you don’t have to overload for all manipulator types):

template<typename R, typename P>
MyDebug & operator<<(R & (*pf)(P &))
{
  stream << pf;
  return *this;
}

Be careful with this last one, because that will also accept regular functions pointers.