Not being able to get backspace character (\b) in the output on ubuntu (K&R example)

Question

#include <stdio.h>
/* replacing tabs and backspaces with visible characters */
int main()
{
  int c;
  while ( (c = getchar() ) != EOF) {
       if ( c == '\t')
          printf("\\t");
       else if ( c == '\b')
          printf("\\b");
       else if ( c == '\\')
          printf("\\\\");
       else 
          putchar(c);
    }

   return 0;
  }

Now my question is .. Why can't I see "\\b" in the output ? I have written this code in Ubuntu terminal. Is there any other way to get the "\\b" character in output ? If there is , please explain in simple words as I have just started learning C programming.This example is from K&R exercise 1-10.

Answer 1

Run the program and enter Ctrl H .

The key-code send by the backspace key (also: <---) is most probably eaten by the shell. This depends on how the terminal is configured. Read here for details: http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html

Answer 2

Is there any other way to get the "\b" character in output ?

If you are supplying the input like:

ab backspace cd

to your program then it'd result in abc because that is what the shell passed to the program.

Ensure that you send the correct input to the program . Invoke it by saying:

printf $'ab\bcd' | /path/to/executable

and it'd print the expected output, ie:

ab\bcd

Answer 3

This is not valid C code. It should look like this:

#include <stdio.h>
/* replacing tabs and backspaces with visible characters */
int main()
{
  int c;
  while ( (c = getchar() ) != EOF) {
       if ( c == '\t')
          printf("\\t");
       else if ( c == '\b')
          printf("\\b");
       else if ( c == '\\')
          printf("\\\\");
       else 
          putchar(c);
   } // <-- note the closing curly brace
   return 0;
}

You should prepare a file containing the \\b ( 0x08 ) and use it as input for your program. Another way would be to press Ctrl - H and then Enter (Thanks @alk for the key combination)