The backspace escape character b unexpected behavior

Question

So I m finally reading through K amp R  and I learned something within the first few pages  that there is a backspace escape character   b   So I go to test it out  and there is some very odd behavior    include  lt stdio h gt   main          printf  hello worl b bd n        The output is  hello wodl   Can anyone explain this

User · Answer

Not too hard to explain     This is like typing hello worl  hitting the left-arrow key twice  typing d  and hitting the down-arrow key   At least  that is how I infer your terminal is interpeting the  b and  n codes   Redirect the output to a file and I bet you get something else entirely   Although you may have to look at the file s bytes to see the difference    edit   To elaborate a bit  this printf emits a sequence of bytes  hello worl H Hd J  where  H is ASCII character  8 and  J is ASCII character  10   What you see on your screen depends on how your terminal interprets those control codes

User · Answer

Your result will vary depending on what kind of terminal or console program you re on  but yes  on most  b is a nondestructive backspace  It moves the cursor backward  but doesn t erase what s there   So for the hello worl part  the code outputs   hello worl                   where   shows where the cursor is  Then it outputs two  b characters which moves the cursor backward two places without erasing  on your terminal     hello worl             Note the cursor is now on the r  Then it outputs d  which overwrites the r and gives us    hello wodl              Finally  it outputs  n  which is a non-destructive newline  again  on most terminals  including apparently yours   so the l is left unchanged and the cursor is moved to the beginning of the next line

User · Answer

lt   pointer to  print head                  part1                printf  hello worl      hello worl              lt   pointer to  print head                  part2                printf   b      hello worl             lt   pointer to  print head                  part3                printf   b      hello worl            lt   pointer to  print head                  part4                printf  d n      hello wodl     lt   pointer to  print head  on the next line

User · Answer

If you want a destructive backspace  you ll need something like    b  b    i e  a backspace  a space  and another backspace

User · Answer

Use a single backspace after each character     printf  hello wor bl bd n

[c] The "backspace" escape character '\b': unexpected behavior?

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