What s the Use of r escape sequence

Question

I have C code like this    include lt stdio h gt  int main         printf  Hey this is my first hello world  r        return 0      I have used the  r escape sequence as an experiment  When I run the code I get the output as   o world   Why is that  and what is the use of  r exactly    If I run the same code in an online compiler I get the output as   Hey this is my first hello world   Why did the online compiler produce different output  ignoring the  r

User · Answer

The program is printing  Hey this is my first hello world    then it is moving the cursor back to the beginning of the line  How this will look on the screen depends on your environment  It appears the beginning of the string is being overwritten by something  perhaps your command line prompt

User · Answer

To answer the part of your question      what is the use of  r    Many Internet protocols  such as FTP  HTTP and SMTP  are specified in terms of lines delimited by carriage return and newline   So  for example  when sending an email  you might have code such as   fprintf socket   RCPT TO   s r n   recipients     Or  when a FTP server replies with a permission-denied error   fprintf client   550 Permission denied r n

User · Answer

This is from antiquated technology   The old fashion typewriter style of printer   There was a roller  platen  that advanced the paper and a print head that hammered a metal key against an ink fabric    r Return the print head to the left side    n Advance the platen one line   If the  n was not issued  you would type over what was on a line  used mostly for underlining text

User · Answer

As amaud576875 said  the  r escape sequence signifies a carriage-return  similar to pressing the Enter key  However  I m not sure how you get  o world   you should  and I do  get  my first hello world  and then a new line  Depending on what operating system you re using  I m using Mac  you might want to use a  n instead of  a  r

User · Answer

r is a carriage return character  it tells your terminal emulator to move the cursor at the start of the line   The cursor is the position where the next characters will be rendered   So  printing a  r allows to override the current line of the terminal emulator   Tom Zych figured why the output of your program is o world while the  r is at the end of the line and you don t print anything after that   When your program exits  the shell prints the command prompt  The terminal renders it where you left the cursor  Your program leaves the cursor at the start of the line  so the command prompt partly overrides the line you printed  This explains why you seen your command prompt followed by o world   The online compiler you mention just prints the raw output to the browser  The browser ignores control characters  so the  r has no effect   See https   en wikipedia org wiki Carriage return  Here is a usage example of  r    include  lt stdio h gt   include  lt unistd h gt   int main             char chars       -                            unsigned int i           for  i   0      i                    printf   c r   chars i   sizeof chars                     fflush stdout                   usleep 200000                      return 0      It repeatedly prints the characters -       at the same position to give the illusion of a rotating   in the terminal

User · Answer

It is quite useful  when you are running on the unix platform  and need to create a text file which will be opened on the dos platform   Unix uses   n  as its line terminator  and dos uses   r n  as its line terminator  so you can use it to create a dos text file

User · Answer

r move the cursor to the begin of the line   Line breaks are managed differently on different systems  Some only use  n  line feed  e g  Unix   some use   r e g  MacOS before OS X afaik  and some use  r n  e g  Windows afaik

User · Answer

The   r  stands for  Carriage Return  - it s a holdover from the days of typewriters and really old printers   The best example is in Windows and other DOSsy OSes  where a newline is given as   r n    These are the instructions sent to an old printer to start a new line   first move the print head back to the beginning  then go down one   Different OSes will use other newline sequences   Linux and OSX just use   n    Older Mac OSes just use   r    Wikipedia has a more complete list  but those are the important ones   Hope this helps   PS   As for why you get that weird output     Perhaps the console is moving the  cursor  back to the beginning of the line  and then overwriting the first bit with spaces or summat

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