Standard no-op output stream

Question

Is there a way to create an ostream instance which basically doesn't do anything ?

For example :

std::ostream dummyStream(...); dummyStream << "Nothing will be printed"; 

I could just create an ostringstream, but data will be buffered (and I really don't want to make anything with them, so it adds a useless overhead).

Any idea ?

[edit] Found this related question which suits my needs. However, I think it could be useful to have a answer saying how to create a valid (no badbit) output stream with standard c++.

Answer 1

You need a custom streambuf.

class NullBuffer : public std::streambuf { public:   int overflow(int c) { return c; } }; 

You can then use this buffer in any ostream class

NullBuffer null_buffer; std::ostream null_stream(&null_buffer); null_stream << "Nothing will be printed"; 

streambuf::overflow is the function called when the buffer has to output data to the actual destination of the stream. The NullBuffer class above does nothing when overflow is called so any stream using it will not produce any output.

Answer 2

If this is to disable logging output, your dummyStream would still cause arguments to be evaluated. If you want to minimize impact when logging is disabled, you can rely on a conditional, such as:

#define debugStream \     if (debug_disabled) {} \     else std::cerr 

So if you have code like:

debugStream << "debugging output: " << foo() << std::endl; 

No arguments will be evaluated if debug_disabled is true.