Carriage return in C?

Question

Output of Following program is : hai

I didn't get how the \r carriage return works in this program and in real can any one help me out ?

#include <stdio.h> #include<conio.h> void main() { printf("\nab"); printf("\bsi"); printf("\rha"); _getch(); }

That's not the output I get (At least once I fix the void main(), and the nonstandard conio.h stuff.) — Billy ONeal
– Billy ONeal, Commented Jan 9, 2011 at 9:46
if you put \n at the end of ab like 'ab\n' will get what you desire? — cristian
– cristian, Commented Jan 9, 2011 at 9:50
@Octopus: I don't think he desires any particular output, he wants to understand the cause of the output he is getting. It is obviously just 'puzzle code' and of no practical use. — Clifford
– Clifford, Commented Jan 9, 2011 at 10:01

icecrime · Accepted Answer · 2011-01-09 09:49:52Z

From 5.2.2/2 (character display semantics) :

\b (backspace) Moves the active position to the previous position on the current line. If the active position is at the initial position of a line, the behavior of the display device is unspecified.

\n (new line) Moves the active position to the initial position of the next line.

\r (carriage return) Moves the active position to the initial position of the current line.

Here, your code produces :

<new_line>ab
\b : back one character
write si : overrides the b with s (producing asi on the second line)
\r : back at the beginning of the current line
write ha : overrides the first two characters (producing hai on the second line)

In the end, the output is :

\nhai

0xHenry · Accepted Answer · 2011-01-09 09:51:02Z

Program prints ab, goes back one character and prints si overwriting the b resulting asi. Carriage return returns the caret to the first column of the current line. That means the ha will be printed over as and the result is hai

Clifford · Accepted Answer · 2011-01-09 10:09:09Z

Step-by-step:

[newline]ab

ab

[backspace]si

asi

[carriage-return]ha

hai

Carriage return, does not cause a newline. Under some circumstances a single CR or LF may be translated to a CR-LF pair. This is console and/or stream dependent.

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