Conditional output
I'd like to create a C++ ostream object that only outputs anything if a condition holds true, to use for debugging. What would be the easiest way to do this? I know that boost has classes that make this easy, but I'd like to know if there's a simple way to do it without boost. The documentation makes it seem like subclassing ostream::sentry would make this possible, but I can't find any source saying that's something that you can/shou开发者_JAVA技巧ld do.
Don't subclass, it's easier to use a wrapper:
class MaybeOstream
{
public:
MaybeOstream(std::ostream& stream_) : stream(stream_), bOutput(true) {}
void enable(bool bEnable) { bOutput = bEnable; }
template<typename T>
MaybeOstream& operator<< (T x)
{
if(bOutput)
stream << x;
return *this;
}
// Add other wrappers around ostream: operator void*, good(), fail(),
// eof(), etc., which just call through to the ostream
private:
std::ostream& stream;
bool bOutput;
}
Take a look at this paper on filtered streambufs.
精彩评论