Need help understanding how \n, \b, and \r will render printf output

Question

I wrote the following program in the C and when I run it, I was surprised by looking at the output.

Here is the program

int main()
{    
       printf("\nab");
       printf("\bsi");    
       printf("\rha");    
}

The output is :- hai whereas I was expecting "absiha" since \n is for new line, \b is for backspace(non erase) and \r is for carriage return. So I was expecting that curson would be at "i" character because \r has been applied but when I run it and saw the output I was totally surprised and confused. Can anyone please explain me the output?

It could be operating system specific.

Basile Starynkevitch
– Basile Starynkevitch

2018-02-15 13:51:24 +00:00
Commented Feb 15, 2018 at 13:51 — Basile Starynkevitch
– Basile Starynkevitch, Commented Feb 15, 2018 at 13:51

Izkata · Accepted Answer · 2012-02-12 21:48:13Z

27

Let's take it one step at a time:

<new line>ab<backspace>si<carriage return>ha

First, handle the backspace. Note that even though it is "non-erase", the next character to be output would overwrite what was backspaced over:

<new line>asi<carriage return>ha

Now, a carriage return means to go back to the beginning of the line. So the "ha" overwrites the "as" in "asi:

<new line>hai

Now, the cursor is currently sitting on the i, so the next character to be output would overwrite i.

answered Feb 12, 2012 at 21:48

Izkata

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2 Comments

Ankur Trapasiya Over a year ago

you mean backspace would just move cursor one position before? just like an insert statement ?

Izkata Over a year ago

@ankur.trapasiya I'm half-guessing that's what you meant by "non-erase", but I've seen it before in other contexts - like, if I have terminal output in a long running program, then hit backspace on the keyboard, the cursor moves over but the character itself stays there until new output is put on top of it. No clue what you mean by "like an insert statement".

Ridox · Accepted Answer · 2014-04-10 05:05:18Z

13

Visit http://en.wikipedia.org/wiki/Escape_sequences_in_C

Escape Sequence Character \a Bell (speaker beeps) \b Backspace (non-erase) \f Form feed/clear screen \n New line \r Carriage Return \t Tab \v Vertical tab \\ Backslash \? Question mark \' Single quote \" Double quote \xnn Hexadecimal character code nn \onn Octal character code nn \nn Octal character code nn

answered Apr 10, 2014 at 5:05

Ridox

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1 Comment

Ankur Trapasiya Over a year ago

thanks for informative answer. Probably you should read the question first.

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