What is the difference between r and n

Question

How are  r and  n different  I think it has something to do with Unix vs  Windows vs  Mac  but I m not sure exactly how they re different  and which to search for match in regexes

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In short  r has ASCII value 13  CR  and  n has ASCII value 10  LF   Mac uses CR as line delimiter  at least  it did before  I am not sure for modern macs    nix uses LF and Windows uses both  CRLF

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in C  I found they use  r n in a string

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They re different characters   r is carriage return  and  n is line feed   On  old  printers   r sent the print head back to the start of the line  and  n advanced the paper by one line  Both were therefore necessary to start printing on the next line   Obviously that s somewhat irrelevant now  although depending on the console you may still be able to use  r to move to the start of the line and overwrite the existing text   More importantly  Unix tends to use  n as a line separator  Windows tends to use  r n as a line separator and Macs  up to OS 9  used to use  r as the line separator   Mac OS X is Unix-y  so uses  n instead  there may be some compatibility situations where  r is used instead though    For more information  see the Wikipedia newline article   EDIT  This is language-sensitive  In C  and Java  for example   n always means Unicode U 000A  which is defined as line feed  In C and C   the water is somewhat muddier  as the meaning is platform-specific  See comments for details

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r is Carriage Return   n is New Line  Line Feed      depends on the OS as to what each means  Read this article for more on the difference between   n  and   r n      in C

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r used for carriage return    ASCII value is 13   n used for new line   ASCII value is 10

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In C and C     n is a concept   r is a character  and  r n is  almost always  a portability bug   Think of an old teletype   The print head is positioned on some line and in some column   When you send a printable character to the teletype  it prints the character at the current position and moves the head to the next column    This is conceptually the same as a typewriter  except that typewriters typically moved the paper with respect to the print head    When you wanted to finish the current line and start on the next line  you had to do two separate steps    move the print head back to the beginning of the line  then move it down to the next line    ASCII encodes these actions as two distinct control characters     x0D  CR  moves the print head back to the beginning of the line    Unicode encodes this as U 000D CARRIAGE RETURN    x0A  LF  moves the print head down to the next line    Unicode encodes this as U 000A LINE FEED     In the days of teletypes and early technology printers  people actually took advantage of the fact that these were two separate operations   By sending a CR without following it by a LF  you could print over the line you already printed   This allowed effects like accents  bold type  and underlining   Some systems overprinted several times to prevent passwords from being visible in hardcopy   On early serial CRT terminals  CR was one of the ways to control the cursor position in order to update text already on the screen   But most of the time  you actually just wanted to go to the next line   Rather than requiring the pair of control characters  some systems allowed just one or the other   For example    Unix variants  including modern versions of Mac  use just a LF character to indicate a newline  Old  pre-OSX  Macintosh files used just a CR character to indicate a newline  VMS  CP M  DOS  Windows  and many network protocols still expect both   CR LF  Old IBM systems that used EBCDIC standardized on NL--a character that doesn t even exist in the ASCII character set   In Unicode  NL is U 0085 NEXT LINE  but the actual EBCDIC value is 0x15    Why did different systems choose different methods   Simply because there was no universal standard   Where your keyboard probably says  Enter   older keyboards used to say  Return   which was short for Carriage Return   In fact  on a serial terminal  pressing Return actually sends the CR character   If you were writing a text editor  it would be tempting to just use that character as it came in from the terminal   Perhaps that s why the older Macs used just CR   Now that we have standards  there are more ways to represent line breaks   Although extremely rare in the wild  Unicode has new characters like    U 2028 LINE SEPARATOR U 2029 PARAGRAPH SEPARATOR   Even before Unicode came along  programmers wanted simple ways to represent some of the most useful control codes without worrying about the underlying character set   C has several escape sequences for representing control codes     a  for alert  which rings the teletype bell or makes the terminal beep  f  for form feed  which moves to the beginning of the next page  t  for tab  which moves the print head to the next horizontal tab position    This list is intentionally incomplete    This mapping happens at compile-time--the compiler sees  a and puts whatever magic value is used to ring the bell   Notice that most of these mnemonics have direct correlations to ASCII control codes   For example   a would map to 0x07 BEL   A compiler could be written for a system that used something other than ASCII for the host character set  e g   EBCDIC    Most of the control codes that had specific mnemonics could be mapped to control codes in other character sets   Huzzah   Portability   Well  almost   In C  I could write printf   aHello  World     which rings the bell  or beeps  and outputs a message   But if I wanted to then print something on the next line  I d still need to know what the host platform requires to move to the next line of output   CR LF   CR   LF   NL   Something else   So much for portability   C has two modes for I O   binary and text   In binary mode  whatever data is sent gets transmitted as-is   But in text mode  there s a run-time translation that converts a special character to whatever the host platform needs for a new line  and vice versa    Great  so what s the special character   Well  that s implementation dependent  too  but there s an implementation-independent way to specify it   n   It s typically called the  newline character    This is a subtle but important point   n is mapped at compile time to an implementation-defined character value which  in text mode  is then mapped again at run time to the actual character  or sequence of characters  required by the underlying platform to move to the next line    n is different than all the other backslash literals because there are two mappings involved   This two-step mapping makes  n significantly different than even  r  which is simply a compile-time mapping to CR  or the most similar control code in whatever the underlying character set is    This trips up many C and C   programmers   If you were to poll 100 of them  at least 99 will tell you that  n means line feed   This is not entirely true   Most  perhaps all  C and C   implementations use LF as the magic intermediate value for  n  but that s an implementation detail   It s feasible for a compiler to use a different value   In fact  if the host character set is not a superset of ASCII  e g   if it s EBCDIC   then  n will almost certainly not be LF   So  in C and C       r is literally a carriage return   n is a magic value that gets translated  in text mode  at run-time to from the host platform s newline semantics   r n is almost always a portability bug   In text mode  this gets translated to CR followed by the platform s newline sequence--probably not what s intended   In binary mode  this gets translated to CR followed by some magic value that might not be LF--possibly not what s intended   x0A is the most portable way to indicate an ASCII LF  but you only want to do that in binary mode   Most text-mode implementations will treat that like  n

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r     Return   n     Newline or Linefeed  semantics  Unix based systems use just a   n  to end a line of text   Dos uses   r n  to end a line of text  Some other machines used just a   r     Commodore  Apple II  Mac OS prior to OS X  etc

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In addition to  Jon Skeet s answer   Traditionally Windows has used  r n  Unix  n and Mac  r  however newer Macs use  n as they re unix based

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r is used to point to the start of a line and can replace the text from there  e g   main     printf   nab    printf   bsi    printf   rha        Produces this output   hai    n is for new line

[special-characters] What is the difference between \r and \n?

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