CS 112 Resources: Cygwin, Eclipse, Windows, Linux, and End-of-Line Characters

Windows and Unix systems (Linux + MacOS X) treat end-of-line differently.

• Windows systems use two characters: CR and LF (ASCII codes '\015' and '\010', respectively).
• Unix systems use one character: LF (010).
• Prior to MacOS X, Macintosh systems used one character: CR (015). Under it GUI interface, MacOS X is a Unix system, so it uses one character: LF (010).

In particular, if the C++ compiler is configured to process the Unix end-of-line character, and getline() is used to read a text file that uses Windows end-of-line characters, the getline() method will not work as expected. To see why, suppose that a text file contains the lines:

   Hello
   Goodbye
   

   Hello\015\010Goodbye\015\010
   

   Hello\010Goodbye\010
   

That is, if getline() is used to read the first line in the file and the C++ compiler is configured for Windows end-of-line characters and we read the file created on Windows, then getline() will read until it has read the CR and LF characters. and then return the string "Hello". Likewise, if the C++ compiler is configured for Unix end-of-line characters and we read the file created on a Unix system, then getline() will read until it has read the LF character, and then return the string "Hello".

The problem comes when you mix and match. For example, if the C++ compiler is configured for Unix end-of-line characters and we read the file created on a Windows system, then getline() will read until it has read the LF character, and then return the string "Hello\015". If you have a unit test that compares whether this string and "Hello" are equal, that test will fail.

• End-of-Line and Cygwin:
  When you run Setup.exe to install and configure cygwin on a Windows system, cygwin will by default configure itself to use and expect Unix-style end-of-line characters:
  

  For situations where you will be moving files back and forth between Windows and Unix systems, this is exactly what you want. You just have to be careful that you create your text files on a Unix system, or create them using a Windows system application that produces Unix system end-of-line characters. (See Eclipse below.)

  If you will be working exclusively in the Windows environment, then you can change cygwin's default using Setup.exe. Run it as before, and when you get to this screen:
  

  click the DOS/text radio button, finish the installation, and cygwin will be configured to use Windows end-of-line characters. But you should only do this if you will never be transferring your projects/files to a Unix system.

• End-of-Line and Eclipse:
  By default, Eclipse uses the end-of-line convention of its host system, so on Windows systems, it uses the CR and LF while on Unix systems, it uses the LF. If you will be using Eclipse on Windows, but you will be moving files back and forth between Windows and Unix, then you want the files you create in Eclipse to use the Unix end-of-line character, To change the default behavior, navigate to

      Window > Preferences > General > Workspace 

  where you will see this screen:
  

  Note that by default, new text files use the system default end-of-line character/delimiter.

  To change this, click the Other radio button and then choose Unix from the pull-down menu:
  

  Click the Ok button to save the change, and any text files that you subsequently create will have Unix end-of-line characters.

  Note that if you have existing text files that are causing problems, you will need to

  1. Copy the text in the file;
  2. Delete the file;
  3. Create a new file with the same name as the old one; and
  4. Paste the text into the new file.

  Or, if you are using Cygwin and have the dos2unix utility installed, you can use it to convert the file from the command-line:

      $ dos2unix -o windowsFile.txt -n unixFile.txt

  The corresponding unix2dos utility can be used to perform the opposite conversion.