c++ newline character under windows command line redirection

Question

I found that Windows command line redirection will replace '\n' with '\r\n' automatically. Is there any method to avoid this situation? Because after stdout or stderr redirection, you will got '\r\r\n' instead of '\r\n' if you write '\r\n' to the console.

Thanks a lot!

you can just try a simple program:

fprintf(stdout,"Hello, world!\r\n");

then you run it with redirection:

demo 1>demo.log

By using any HEX editor, you will find that '\r\n' is represented by '\r\r\n'.

UPDATE:

@steve-jessop I have solved this problem by using setmode, which will force stdout using O_BINARY mode. So the stream won't translate \n into \r\n.

Thanks a lot!

Steve Jessop · Accepted Answer · 2011-07-31 18:02:45Z

The way to avoid it is to not write "Hello, world!\r\n". Either fprintf(stdout,"Hello, world!\n"); or std::cout << "Hello, world!" << std::endl; is sufficient.

This isn't particular to command-line redirection or stdout, the same would be true with any file descriptor open in character mode (as opposed to binary mode).

the thing is that std::endl is not just a new line, it also flushes and has impact on performance depending where added

Martin Green · Accepted Answer · 2011-07-31 18:24:05Z

6

'\n' is the platform-independent newline representation. It's expanded by the compiler to whatever is the actual newline representation for the platform you're compiling for -- '\r\n' for Windows, and '\n' for *nix and friends, including MacOS.

So this is why you see '\r\r\n' in hex editor -- '\n' from '\r\n' that you wrote in source was expanded to '\r\r\n'.

answered Jul 31, 2011 at 18:24

Martin Green

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3 Comments

Steve Jessop Over a year ago

It's not expanded by the compiler, it's expanded by the stream when it's written. strlen("\n") is always 1.

Martin Green Over a year ago

@Steve Thanks for the correction! I had somehow gotten it into my head that it was a compile-time thing, not runtime. One quick experiment later I see that I was wrong.

Michas Over a year ago

You mean MacOS X. It is '\r' for classic MacOS.

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