Difference between endl and '\n'

Question

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C++: “std::endl” vs “\n”

I have a simple program I tested and I realise that endl wreaks havoc on my program. Using endl, my program ran in 100+ ms while working with '\n', the time dropped to ~50ms. Can anyone tell why is there such a difference?

P.S. I did read other posts that somehow explained what each of them are doing, but does std::flush really take so much time?
Or could there be another possible explanation?

3

endl also flushes the buffer. – Duck Nov 24 '12 at 21:42

score 6 · Answer 1 · answered Nov 24 '12 at 21:42

6

std::endl writes a newline, and flushes the buffer. As you have discovered, the flush can be a rather expensive operation.

answered Nov 24 '12 at 21:42

NPE

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It's quite strange to me that this thing can double the execution time. Thank you – Mihai Bujanca Nov 24 '12 at 21:47
@BujancaMihai: If there's doubt in your mind, compare the timings of: (1) `endl`; (2) `\n`; (3) `\n` followed by `flush`. – NPE Nov 24 '12 at 21:50
No doubt, I already tried and the difference is obvious. I was aware that the `flushing` occurs but not that it is such an expensive operation. Many thanks – Mihai Bujanca Nov 24 '12 at 21:51
@BujancaMihai: maybe the cost of the flush depends on how much things you have to flush, so it's hard to predict how expensive the operation will be. – effeffe Nov 25 '12 at 00:53

score 2 · Accepted Answer · answered Nov 24 '12 at 21:54

endl has extra expensive flush() operation

27.7.3.8 Standard basic_ostream manipulators [ostream.manip]

namespace std {
template <class charT, class traits>
basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os);
}
1 Effects: Calls os.put(os.widen(’\n’)), then os.flush().
2 Returns: os.

Difference between endl and '\n'

2 Answers2