Proposal new check endl << endl

[federico]

In a project I noticed following pattern

void f()
{
std::cout << "a" << std::endl << std::endl;
}

And a similar patterns one with flush, like "std::endl << std::flush"

Fortunately, it was easy to write a custom check

<?xml version="1.0"?>
<rule version="1">
    <pattern>std :: (endl|flush) &lt;&lt; std :: (endl|flush)</pattern>
    <message>
        <id>redundantCondition</id>
        <severity>performance</severity>
    <summary>Multiple flushes. Consider flushing only once, and replacing "std::endl" with "\n"</summary>
    </message>
</rule>

I would prefer if cppcheck would do a similar verification by itself; what are the criteria for adding a new check in cppcheck?

Note that this pattern is not an error per se, but it hurts performance, as in general "\n" will already do a flush, and std::endl always flushes.

[CHR]

clang -tidy detects any endl usage as performance-avoid-endl.

[Daniel Marjamäki]

I am not against it. your suggestion sounds less aggressive than clang-tidy 👍

The main criteria is that it will be low noise. And well if you warn about redundant flushes that does not sound very noisy to me.

[federico]

Exactly, warning about all std::endl might be too much (used in a lot of places, and it might be intended), while two consecutive flushes is most likely unintended.