“std::endl” vs “\n”

Question

Many C++ books contain example code like this...

std::cout << \"Test line\" << std::endl;

...so I\'ve always done that too. But

Answer 1

If you use Qt and endl, you could accidentally end up using an incorrect endl which gives you very surprising results. See the following code snippet:

#include 
#include  
#include 

// notice that there is no "using namespace std;"
int main(int argc, char** argv)
{
    QApplication qapp(argc,argv);
    QMainWindow mw;
    mw.show();
    std::cout << "Finished Execution!" << endl;
    // This prints something similar to: "Finished Execution!67006AB4"
    return qapp.exec();
}

Note that I wrote endl instead of std::endl (which would have been correct) and apparently there is a endl function defined in qtextstream.h (which is part of QtCore).

Using "\n" instead of endl completely sidesteps any potential namespace issues. This is also a good example why putting symbols into the global namespace (like Qt does by default) is a bad idea.