What does it mean to flush the output in competitive programming?

Question

I am currently giving codechef long challenge and there they are asking to flush the output after printing each line. How to use flush in cpp and how does this affect the time limit if I am not using flush? Currently I am using this code-

cout<<z<<" "<<endl;
cout.flush();

You're flushing twice: `<< std::endl` is equivalent to `<< '\n' << std::flush`. — Quentin, Dec 10 '18 at 14:06

score 3 · Answer 1 · answered Dec 10 '18 at 14:06

3

Flushing makes output slower, because it cannot buffer 2 lines and output them at once.

However, std::endl already flushes for you.

You can send an endline without flushing by printing '\n'.

As an aside, you might want to std::ios_base::sync_with_stdio(false); to improve io speed if you aren't using C based IO.

answered Dec 10 '18 at 14:06

Yakk - Adam Nevraumont

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Flushing *might* make output slower. It could also have no effect on the performance, because the receiving system is fast enough to consume the unbuffered output. – Caleth Dec 10 '18 at 15:01
@Caleth I guess that is possible, but there aren't many teletype machines left. – Yakk - Adam Nevraumont Dec 10 '18 at 15:10

What does it mean to flush the output in competitive programming?

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