Derive from ostream or ostream_iterator to make a stream pretty printer in C++?

Question

I have code which dumps a representation of complex objects to a stream. The representation uses open and close curly brackets to denote the start and end of nested objects. Rather than pretty print the representation format, I feel it's better to leave all whitespace out of the raw output and implement pretty printing, if desired, as a decorator pattern.

The pretty print algorithm is simply: examine next char to output, if it is a close brace, output newline + close brace + newline. Else just output the char.

I could implement this decorator as a class derived from ostream_iterator or as a class derived from ostream. Which is more commonly done? Are there any downsides to creating an ostream wrapper?

Answer 1

The only reason where it is advisable to derive from std::ostream is when using the derived class to construct an std::streambuf and initialize the the base std::ostream with it. I don't think there is ever a reason to derive from std::ostream_iterator<...> at all.

Instead you'd derive from std::streambuf and override overflow() to do whatever filter operation you want to do. For convenience you might then derive from std::ostream to construct a convenience stream.