"std::endl" vs "\n"

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 can be illustrated by the following:

std::cout << std::endl;

is equivalent to

std::cout << '\n' << std::flush;

So,

• Use std::endl If you want to force an immediate flush to the output.
• Use \n if you are worried about performance (which is probably not the case if you are using the << operator).

I use \n on most lines.
Then use std::endl at the end of a paragraph (but that is just a habit and not usually necessary).

Contrary to other claims, the \n character is mapped to the correct platform end of line sequence only if the stream is going to a file (std::cin and std::cout being special but still files (or file-like)).

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.

Not a big deal, but endl won't work in boost::lambda.

(cout<<_1<<endl)(3); //error

(cout<<_1<<"\n")(3); //OK , prints 3

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 <iostream>
#include <QtCore/QtCore> 
#include <QtGui/QtGui>

// 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.

Something that I've never seen anyone say is that '\n' is affected by cout formatting:

#include <iostream>
#include <iomanip>

int main() {
    std::cout << "\\n:\n" <<  std::setw(2) << std::setfill('0') << '\n';
    std::cout << "std::endl:\n" << std::setw(2) << std::setfill('0') << std::endl;
}

Output:

\n:
0
std::endl:

Notice, how since '\n' is one character and fill width is set to 2, only 1 zero gets printed before '\n'.

I can't find anything about it anywhere, but it reproduces with clang, gcc and msvc.

I was super confused when I first saw it.