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Debajit Adhikary
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 Posted: Mon Oct 18, 2004 8:13 pm Post subject: 'n' vs std::endl for Displaying Newlines |
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(1) In what cases is std::endl better than a trailing n for
displaying a newline, for instance, at the end of some std::cout
statement? (I'm looking for concrete examples)
(2) Which all buffers does std::endl flush?
(3) Is something like
std::cout << "some textn";
*always* faster than
std::cout << "some text" << std::endl;
?
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Ron Natalie
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| Posted: Tue Oct 19, 2004 4:34 pm Post subject: Re: 'n' vs std::endl for Displaying Newlines |
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Debajit Adhikary wrote:
| Quote: | (1) In what cases is std::endl better than a trailing n for
displaying a newline, for instance, at the end of some std::cout
statement? (I'm looking for concrete examples)
|
It's only necessary if you want to see the output and there is some
time that passes before what another buffer flush. However, it's
rare that makes a difference. The few times you really care, like
you're about to do some input, already force a flush otherwise.
| Quote: |
(2) Which all buffers does std::endl flush?
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It flushes the stream buffer associated with whatever ostream
you invoke it on.
| Quote: |
(3) Is something like
std::cout << "some textn";
*always* faster than
std::cout << "some text" << std::endl;
It's not ALWAYS faster, but it probably never will never be slower. |
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Milivoj Davidov
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| Posted: Tue Oct 19, 2004 6:00 pm Post subject: Re: 'n' vs std::endl for Displaying Newlines |
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"Debajit Adhikary" <debajit1 (AT) gmail (DOT) com> wrote
| Quote: | (1) In what cases is std::endl better than a trailing n for
displaying a newline, for instance, at the end of some std::cout
statement? (I'm looking for concrete examples)
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See James Kanze's first reply to your original posting.
I'd also say that std::endl is always better than 'n'
(except when you are optimizing known performance bottlenecks).
Std::endl provides expected and correct behaviour,
especially in cases of applications with multiple
processes, e.g. back-end, unattended servers.
Using 'n' is an optimisation technique, it can lead to loss of
data, and data out of order; its performance is less predictable.
| Quote: | (2) Which all buffers does std::endl flush?
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See first reply to your OP.
For example: std::cout << std::endl flushes std::cout's buffer,
whereas mystream << std::endl flushes mystream's buffer
(assuming mystream is an std::ostream, or std::ofstream, etc.).
| Quote: | (3) Is something like
std::cout << "some textn";
*always* faster than
std::cout << "some text" << std::endl;
?
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See first reply to your OP. (No, not always.)
Additionally, 'n' is not faster when a buffer flush occurs
at its write (with no buffer flush it should be *much* faster).
Milivoj Davidov
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hari4063
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| Posted: Wed Oct 20, 2004 4:14 pm Post subject: Re: 'n' vs std::endl for Displaying Newlines |
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Main difference is that std::endl DOES flushing, and n does not. If You
look at implementation, endl is not defined like string, it is function (I
think). So, it can be faster to write new line with "n".
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