Many C++ books contain example code like this...
std::cout << "Test line" << std::endl;
...so I've always done that too. But I've seen a lot of code from working developers like this instead:
std::cout << "Test line\n";
Is there a technical reason to prefer one over the other, or is it just a matter of coding style?
There might be performance issues, std::endl forces a flush of the output stream.
They will both write the appropriate end-of-line character(s). In addition to that endl will cause the buffer to be committed. You usually don't want to use endl when doing file I/O because the unnecessary commits can impact performance.
I've always had a habit of just using std::endl because it is easy for me to see.
The varying line-ending characters don't matter, assuming the file is open in text mode, which is what you get unless you ask for binary. The compiled program will write out the correct thing for the system compiled for.
The only difference is that std::endl flushes the output buffer, and '\n' doesn't. If you don't want the buffer flushed frequently, use '\n'. If you do (for example, if you want to get all the output, and the program is unstable), use std::endl.
The difference:
std::cout << std::endl;
// is equivalent too
std::cout << "\n" << std::flush();
Use std::endl if you are in a command line app and want to guarantee that the user can see the output immediately.
Use "\n" if you are in a worried about performance (which is probably not the case if you are using the << operator).
I use std::endl mostly out of habit.
Contrary to other claims the "\n" character is mapped to the correct platform end of line sequence if the stream is going to a file (std::cin and std::cout being special but still files (or file like))
Not a big deal, but endl won't work in boost::lambda.
(cout<<_1<<endl)(3); //error
(cout<<_1<<"\n")(3); //OK , prints 3
There's another function call implied in there if you're going to use std::endl
a) std::cout << "Hello\n";
b) std::cout << "Hello" << std::endl;
a calls operator<< once b calls operator<< twice
If you use Qt and endl, you could accidentally use the wrong endl, happened to me today and i was like ..WTF ??
#include <iostream>
#include <QtCore/QtCore>
#include <QtGui/QtGui>
//notice that i dont have a "using namespace std;"
int main(int argc, char** argv)
{
QApplication qapp(argc,argv);
QMainWindow mw;
mw.show();
std::clog << "Finished Execution !" << endl << "...";
// Line above printed: "Finished Execution !67006AB4..."
return qapp.exec();
}
Of course that was my mistake, since i should have written std::endl, but if you use endl, qt and using namespace std; it depends on the order of the include files if the correct endl will be used.
Of course you could recompile Qt to use a namespace.
EDIT: Forgot to mention, Qt's endl is declared in "qtextstream.h" which is part of QtCore