Changing std::endl to put out CR+LF instead of LF

问题:

I'm writing a program on a Linux platform that is generating text files that will be viewed on, inevitably, a Windows platform.

Right now, passing std::endl into a ostream generates the CR character only for newlines. Naturally, these text files look wrong in MS Notepad.

1. Is there a way to change std::endl such that it uses CR+LF for newline instead of LF?
2. I know I could write my own custom manipulator, like win_endl, for generating my own newlines, but I use the std::endl symbol in a lot of places, and like many programmers, have a tendency to do the thing that requires the least work possible. Could I simply overload std::endl to produce CR+LF, or is this a dumb idea for maintainability?

NB: I checked out this question, but it's asking about going the other way, and the accepted answer seems rather incomplete.

回答1:

Opening a file in text mode should cause std::endl to be converted to the appropriate line ending for your platform. Your problem is that newline is appropriate for your platform, but the files you create aren't intended for your platform.

I'm not sure how you plan on overloading or changing endl, and changing its behavior would certainly be surprising for any developers new to your project. I'd recommend switching to win_endl (should be a simple search-and-replace) or maybe switching from a standard ostream to a Boost.Iostreams filtering stream to do the conversion for you.

回答2:

std::endl is basicly:

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

So just use "\r\n" instead and omit the flush. It's faster that way, too!

From the ostream header file on endl:

This manipulator is often mistakenly used when a simple newline is desired, leading to poor buffering performance.

回答3:

Windows Notepad is pretty much the only Windows program you'll find that doesn't handle LF-only files properly. Almost everything else (including WordPad) handles LF-only files just fine.

This problem is a bug in Notepad.

回答4:

You shouldn't use \r\n. Just use \n, but then open the stream in "text" mode, which than will do the conversion for you. You may not care about cross-platform, but this is the official way of doing it.

That way, the same code will spit-out \n on unix, \r\n on windows, and \r on mac.

回答5:

Here was my solution to the problem. It's a bit of a mash-up of all the info provided in the answers:

1. I created a macro in a win_endl.h file for the newline I wanted:

   #define win_endl "\r\n"
   

2. Then I did a search-and-replace:

   sheepsimulator@sheep\_machine > sed -i 's/std::endl/win_endl' *
   

And ensured all my files included win_endl.h.