std::flush
right after a std::endl
is used all over the legacy code I am looking at. When I first saw this, my thought was it is redundant from looking at the description of std::endl
and std::flush
at:
http://en.cppreference.com/w/cpp/io/manip/endl
http://en.cppreference.com/w/cpp/io/manip/flush
Here is an example of what I am seeing in the legacy source code:
std::cout << "Generic Notification" << std::endl << std::flush;
But, as many senior software developers have seen this code throughout the years, I am wondering if there is some detail I am missing. Is there any purpose to having a std::flush
after a std::endl
?
There's no purpose for it.
If I had to speculate on why your legacy code contains these lines, there are a few possibilities, starting with (what I consider to be) the most probable scenarios:
std::flush
mistakenly, and the senior developers didn't consider it a problem needing fixing std::endl
did not trigger a flush, which meant that your senior developers were (correctly) understanding that it was necessary std::endl
to trigger a flush std::endl
. In a standards-compliant environment, std::flush
serves no useful purpose in this code.
Whoever wrote this either didn't fully understand the semantics of std::endl
, or were working around some limitation of their compiler or execution environment.
I'll add to the other valid answers that, very often, there isn't a good purpose for either std::flush
nor std::endl
.
Basically, std::endl
= start a new line + flush the stream. A lot of people, though, tend to end their lines with std::endl
because it "sounds right" - end the line. But we actually rarely need to flush the output stream. Sometimes we do (eg when we're expecting a user's reply to the string, or it's important to monitor our output with minimal delay) - but that's the exception, not the rule.
So, it might take a bit of getting used to, but we should really default to simply:
std::cout << bunch_of_stuff << '\n';
and that's that!
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