Usage of b and r in C

Question

b and  r are rarely used in practice  I just found out that I misunderstood these two escape sequences  A simple test   printf  foo bbar n      I expected it to output fobar  because  b will backspace the cursor  and b will overwrite the second o  but instead it outputs  foobar  The same is with  r   printf  foo rbar n      I thought  r will move the cursor to the beginning of the current line  so bar will replace foo  so the final output should be bar  However  it actually outputs   foo bar

User · Answer

The characters are exactly as documented -  b equates to a character code of 0x08 and  r equates to 0x0d  The thing that varies is how your OS reacts to those characters  Back when displays were trying to emulate an old teletype those actions were standardized  but they are less useful in modern environments and compatibility is not guaranteed

User · Answer

The interpretation of the backspace and carriage return characters is left to the software you use for display  A terminal emulator  when displaying  b would move the cursor one step back  and when displaying  r to the beginning of the line  If you print these characters somewhere else  like a text file  the software may choose  to do something else

User · Answer

I have experimented many of the backslash escape characters   n which is a new line feed can be put anywhere to bring the effect  One important thing to remember while using this character is that the operating system of the machine we are using might affect the output  As an example  I have printed a bunch of escape character and displayed the result as follow to proof that the OS will affect the output   Code    include  lt stdio h gt  int main void       printf  Hello World         printf  Goodbye  a        printf  Hi  b        printf  Yo f        printf  What   t        printf  pewpew        return 0

User · Answer

As for the meaning of each character described in C Primer Plus  what you expected is an  correct  answer  It should be true for some computer architectures and compilers  but unfortunately not yours   I wrote a simple c program to repeat your test  and got that  correct  answer  I was using Mac OS and gcc    Also  I am very curious what is the compiler that you were using

User · Answer

The characters will get send just like that to the underlying output device  in your case probably a terminal emulator    It is up to the terminal s implementation then how those characters get actually displayed  For example  a bell   a  could trigger a beep sound on some terminals  a flash of the screen on others  or it will be completely ignored  It all depends on how the terminal is configured

[c] Usage of \b and \r in C

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