Line terminators

What are difference between:

• \r\n - Line feed followed by carriage return.
• \n - Line开发者_Python百科 feed.
• \r - Carriage Return.

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They are the line terminator used by different systems:

• \r\n = Windows
• \n = UNIX and Mac OS X
• \r = Old Mac

You should use std::endl to abstract it, if you want to write one out to a file:

std::cout << "Hello World" << std::endl;

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In general, an \r character moves the cursor to the beginning of the line, while an \n moves the cursor down one line. However, different platforms interpret this in different ways, leading to annoying compatibility issues, especially between Windows and UNIX. This is because Windows requires an \r\n to move down one line and move the cursor to the start of the line, whereas on UNIX a single \n suffices.

Also, obligatory Jeff Atwood link: http://www.codinghorror.com/blog/2010/01/the-great-newline-schism.html

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Historical info

The terminology comes from typewriters. Back in the day, when people used typewriters to write, when you got to the end of a line you'd press a key on the typewriter that would mechanically return the carriage to the left side of the page and feed the page up a line. The terminology was adopted by computers and represented as the ascii control codes 0xa, for the linefeed, and 0xd for the carriage return. Different operating systems use them differently, which leads to problems when editing a text file written on a Unix machine on a Windows machine and vice-versa.

Pragmatic info

On Unix based machines in text files a newline is represented by the linefeed character, 0xa. On Windows both a linefeed and carriage return are used. For example when you write some code on Linux that has the following in it where the file was opened in text mode:

fprintf(f, "\n");

the underlying runtime will insert only a linefeed character 0xa to the file. On Windows it will translate the \n and insert 0xd0xa. Same code but different results depending on the operating system used. However this changes if the file is opened in binary mode on Windows. In this case the insertion is done literally and only a linefeed character is inserted. This means that the sequence you asked about \r\n will have a different representation on Windows if output to a binary or text stream. In the case of it being a text stream you'll see the following in the file: 0xd0xd0xa. If the file was in binary mode then you'll see: 0xd0xa.

Because of the differences in how operating systems represent newlines in text files text editors have had to evolve to deal with them, although some, like Notepad, still don't know what to do. So in general if you're working on Windows and you're given a text file that was originally written on a Unix machine it's not a good idea to edit it in Notepad because it will insert the Windows style carriage return linefeed (0xd0xa) into the file when you really want a 0xa. This can cause problems for programs running on old Unix machines that read text files as input.

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See http://en.wikipedia.org/wiki/Newline

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Different operating systems have different conventions; Windows uses \r\n, Mac uses \r, and UNIX uses \n.

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1. \r

   This sends the cursor to the beginning column of the display

2. \n

   This moves the cursor to the new line of the display, but the cursor stays in the same column as the previous line.

3. \r\n

   Combine 1 and 2. The cursor is moved to the new line, and it is also moved to the first column of the display.

Some compilers prints both a new line and carriage return when you specify only \n.