Why does using std::endl with ostringstream affect output speed?

Question

I\'m timing the difference between various ways to print text to standard output. I\'m testing cout, printf, and ostringstream using both

Answer 1

Each output operation on a stream dors multiple steps:

• It checks if the stream is in good shape.
• It checks if some other stream needs to flushed.
• The sequence of characters is produced.
• It checks if there is enough space for the written characters.
• The use of endl calls an extra virtual function on the stream buffer.

I would personally expect that the extra virtual function call actually has relativly small impact compared to the other operations. You can verify this guess by also profiling this output:

out << "stream" << '\n';

... or even

out << "stream" << out.widen('\n');

That said, there are a number of improvements which a stream implementation can apply to cut down on checks. Whether this is done will depend on the implementation, of course.