Carriage Return "\r" character working like new line "\n" character on MacBook. Any tips ?

[Lakshman Subramanya]

Hello,

I use Eclipse (kepler version, with JDK 7) on MacBook Pro (Lion)

I want to overwrite a line printed on my console. I used "\r" for that. I was expecting the cursor to go to the beginning of the line. Instead, it is going to the next line.
Could some one tell me how to rectify this problem ?

Code:
------

System.out.print("Superman\rSober");


Expected Output:
----------------
Soberman


Actual Output:
----------------
Superman
Sober

Any help appreciated.

[Ashwin Raghavan]

not sure if i understood you correct. currently your output is

superman
sober

and you want it to become
Soberman

is that correct?

[Lakshman Subramanya]

Yes. Thats right.

[Campbell Ritchie]

How old is your Mac? Macs used to use \r as their line end, but for the last few years they have changed to \n
The behaviour of \r is platform‑dependent. If I try

System.out.println("Campbell\ris\great");

…it will print greatell on this PC running Windows® and running Linux on the same machine I get a blank line.

[Winston Gutkowski]

Lakshman Subramanya wrote:Could some one tell me how to rectify this problem ?

Simple answer: with custom code.

As Campbell has already pointed out, the behaviour of '\r' is platform-dependant and not necessarily what you want. You could, however, emulate it with something like:

public static final String overlay(String line) {
   String[] portions = line.split("\r");
   if (portions.length < 2)
      return line;

   StringBuilder sb = new StringBuilder();
   for (String portion : portions) {
      sb.replace(0, portion.length, portion);
   }
   return sb.toString();
}

I should add that this is only ONE way of doing it. There are plenty of others. You should also make sure that 'line' is in fact a single line before you call it because, on a Windows system, a multi-line String could contain '\r's that are part of the CRLF pattern.

HIH

Winston

[Lakshman Subramanya]

Hi Winston, Campbell,
Thanks for the response and the alternate idea.

I figured out \r and \b behaves incorrectly when the program is ran through Eclipse IDE and its console on Mac OSX. It works fine when I run it through Mac Terminal app (command line).

Example:

public class LineControlCharacters {
	public static void main(String[] args){
		System.out.println("Hexagon\rOcta");
		System.out.println("Hexagon\bOcta");
		System.out.println("Hexagon\tOcta");
		System.out.println("Hexagon\nOcta");		
	}
}

		/*
			Output on Max OS X (Lion) Terminal (command line):
			 	Octagon
				HexagoOcta
				Hexagon	Octa
				Hexagon
				Octa 
		
			Output on Eclipse (Kepler) - Console on Max OS X (Lion):
				Hexagon
				Octa
				HexagonOcta
				Hexagon	Octa
				Hexagon
				Octa
		*/
 

[Campbell Ritchie]

Lakshman Subramanya wrote:Hi Winston, Campbell,
Thanks for the response and the alternate idea.

You're welcome

. . . \r and \b behaves incorrectly when the program is ran through Eclipse IDE and its console on Mac OSX.
. . .

What do yoiu mean by “behaves incorrectly”? Have you found anywhere that defines the behaviour of \r and \b? You mean it behaves differently. I do not know how the console on Eclipse handles those characters, and not having a Mac I don't think I can try it and find out.

[Winston Gutkowski]

Lakshman Subramanya wrote:I figured out \r and \b behaves incorrectly when the program is ran through Eclipse IDE and its console on Mac OSX. It works fine when I run it through Mac Terminal app (command line).

My worry here is that your program is likely to be very platform-specific. Indeed, yours is likely to become terminal-specific, which is arguably even worse.

The problem is that you may be able to emulate the overlay characteristics you want, but cursor placement is another thing completely. For example, on many terminals '\b' may NOT necessarily be destructive, so
System.out.println("Hexagon\tOcta\b\b\b");
might well produce:
Hexagon Octa
(the underline shows where the cursor will be),
and
System.out.println("Hexagon\tOcta\b\b\bX");
something like:
Hexagon OXta

My point is that either:
(a) You need to decide what the display rules are.
(b) You need to choose a terminal that does what you want and document it in your program.

HIH

Winston

[vikas byn]

Lakshman Subramanya wrote:Hello,

I use Eclipse (kepler version, with JDK 7) on MacBook Pro (Lion)

I want to overwrite a line printed on my console. I used "\r" for that. I was expecting the cursor to go to the beginning of the line. Instead, it is going to the next line.
Could some one tell me how to rectify this problem ?

Code:
------

System.out.print("Superman\rSober");


Expected Output:
----------------
Soberman


Actual Output:
----------------
Superman
Sober

Any help appreciated.

Its a bug in eclipse. Run your program on terminal/command promt

[Campbell Ritchie]

How do you know it is a bug?

[Campbell Ritchie]

Last November, I wrote: . . .

System.out.println("Campbell\ris\great");

. . .

I think that should really be

System.out.println("Campbell\ris\rgreat");

[John Canon]

Campbell Ritchie wrote:How do you know it is a bug?

https://bugs.eclipse.org/bugs/show_bug.cgi?id=76936 (bug first reported in 2004, still open ...)

:-)

[Campbell Ritchie]

Thank you. And welcome to the Ranch