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 <<         


        

Answer 1

For runtime-controllable redirection of log messages, a self-contained solution combining the ideas of john and Sjoerd:

class DebugStream {
private:
    class NullStream : public std::ostream {
    private:
        class NullBuffer : public std::streambuf {
        public:
            int overflow(int c) override { return c; }
        } buffer_;
    public:
        NullStream() : std::ostream(&buffer_) {}
    } null_;

    std::ostream &output_;
    bool enabled_;

public:
    DebugStream(std::ostream &output = std::cout) : output_(output), enabled_(false) {}
    void enable(const bool enable) { enabled_ = enable; }

    template  std::ostream& operator<<(const T &arg) {
        if (enabled_) return output_ << arg;
        else return null_ << arg;
    }
};

extern DebugStream debug_stream;
#define TRACE_ENABLE(x) debug_stream.enable(x)
#define TRACELN(x) debug_stream << x << std::endl
#define TRACE(x) debug_stream << x

Then you can do stuff like:

TRACELN("The value of x is " << x " and the value of y is " << y);

It would also be easy to just remove the trace statements from a release version completely with #define the trace macros to empty statements.

You still need to define debug_stream somewhere global, though.