Question

It was many years now since I stopped using std::endl to end lines when writing to std::cout, and started using "\n" instead.

But now I start seeing more snippets of code using '\n' instead, and I started wonder what might be best.

Besides the obvious that one is a string, and the other a character, is there any advantage to using this:

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

Over this:

std::cout << variable << "\n";

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Late addition:

When I asked this question I seemed to think that newline '\n' flushed the buffer. Now I know that it depends.

By default std::cin is tied to the old C stdin FILE* stream, and std::cout is tied to stdout. The flushing on newline comes from this tying. By default stdout, if connected to a terminal, is line-buffered. That means a new line will flush its buffers. So when printing a newline using std::cout, that will lead to stdout being flushed.

If stdout is not connected to a terminal (for example the output has been redirected or is piped), or if the tie between std::cout and stdout is broken, then newlines will not flush anything.

Answer 1

Actually, '\n' should be the default. Unless you want to also explicitly flush the stream (and when and why would you want to do that?), there is no need to use std::endl at all.¹
Of course, many books and tutorials use std::endl as the default. That is unfortunate and might lead to serious performance bugs.

I suppose there’s little difference between using '\n' or using "\n", but the latter is an array of (two) characters, which has to be printed character by character, for which a loop has to be set up, which is more complex than outputting a single character. Of course, when doing IO this rarely matters, but if in doubt, when you want to output one character literal, output a character literal, rather than a whole string literal.
A nice side-effect of doing so is that you communicate in your code that you intended to output only a single character, and not just accidentally did this.

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^{1 _{Note that std::cout is tied to std::cin by default, which leads to std::cout being flushed before any input operation, so that any prompt will be printed before the user has to input something.}}