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1. 

   StephenFromNYC
   Moderator

   Wednesday September 8, 2010

   Hello,

   I was looking at the source code files located in the directory:

   \hardware\leaflabs\cores\maple\*.*

   I am probably missing something subtle. I thought "\r\n" was used in Linux (and flavors of Linux, including Mac OS), but that Windows/DOS needed only "\n".

   I was surprised when I saw "\r" in several files.

   From file: Print.cpp

   void Print::println(void)
   {
   print('\r');
   print('\n');
   }

   From file: usb.c [function void usbSendHello(void)]

   char *line = "\r\n";

   From file: syscalls.c [function void cgets(char *s, int bufsize)]

   case '\r' :
   case '\n' :
   putch('\r');
   putch('\n');
   *p = '\n';
   return;

   I am using Windows XP Professional SP3 and Maple IDE 0.0.6.

   Thanks!

   Stephen from NYC

   Posted 5 years ago #
2. 

   snigelen
   Member

   For text-files it's the other way around; Unix (including Linux) traditionally use '\n' to terminate lines and Windows (and DOS) uses "\r\n". But when it comes to serial communication with a terminal program they often interpret '\r' (carriage return) and '\n' (line feed) more literary. Often you can tell the terminal program what behavior you want. But "\r\n" seems to be default to move to the beginning of the next line with the terminal programs I used (mostly on Unix). (Maybe there's some standard in serial communication, I don't know).

   Posted 5 years ago #
3. 

   gbulmer
   Moderator

   I believe sniglen is correct.

   Unix (Linux, xBSD, AIX, HPUX, etc., and, AFAIK, Mac OS X) all had/have smart device drivers. The device driver is part of the kernel, and it normally decides what to do to get the effect of '\n' on those systems.

   As far as I can remember (I was quite young once :-), CP/M (which begat DOS, which begat Windows) did not have smart device drivers, so files contained the characters which normally drove the terminal or printer, which needed both line-feed and carriage return (only one or the other was not enough)

   The sneaky thing about doing a putch('\r'); putch('\n'); is that it should work correctly for both types of system.

   On a UNIX-ish system, and Windows, the '\r' should be interpreted as 'go back to the starting margin' (I'm ignoring the differences of which written language is in use at this point).

   On UNIX-ish systems, the '\n' can be safely interpreted as carriuage return (which it's just done, but UNIX tends to be very obedient, and doesn't mind doing it twice :-) followed by a line feed.

   On Windows, the '\n' can be interpreted as a line feed (it just did a carriage return so the cursor should be at the start of the line anyway).

   Clever, eh?

   Posted 5 years ago #

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