问题
I understand the difference between the two so there's no need to go into that, but I'm just wondering what the reasoning is behind why Windows uses both CR and LF to indicate a line break. It seems like the Linux method (just using LF) makes a lot more sense, saves space, and is easier to parse.
回答1:
Historically when using dot-matrix printers teletypes CR would return the carriage to the first position of the line while LF would feed to the next line. Using CR+LF in the file themselves made it possible to send a file directly to the printer, without any kind of printer driver.
Thanks @zaph pointing out it was teletypes and not dot matrix printers
回答2:
@sshannin posted an URL from Raymond Chen's blog, but it doesn't work anymore. The blog has changed its internal software, so the URLs changed.
After crawling through the old posts in the new blog I've found it here.
Quote from the blog:
Why is the line terminator CR+LF?
This protocol dates back to the days of teletypewriters. CR stands for “carriage return” – the CR control character returned the print head (“carriage”) to column 0 without advancing the paper. LF stands for “linefeed” – the LF control character advanced the paper one line without moving the print head. So if you wanted to return the print head to column zero (ready to print the next line) and advance the paper (so it prints on fresh paper), you need both CR and LF.
If you go to the various internet protocol documents, such as RFC 0821 (SMTP), RFC 1939 (POP), RFC 2060 (IMAP), or RFC 2616 (HTTP), you’ll see that they all specify CR+LF as the line termination sequence. So the the real question is not “Why do CP/M, MS-DOS, and Win32 use CR+LF as the line terminator?” but rather “Why did other people choose to differ from these standards documents and use some other line terminator?”
Unix adopted plain LF as the line termination sequence. If you look at the stty options, you’ll see that the onlcr option specifies whether a LF should be changed into CR+LF. If you get this setting wrong, you get stairstep text, where
each
line
begins
where the previous line left off. So even unix, when left in raw mode, requires CR+LF to terminate lines. The implicit CR before LF is a unix invention, probably as an economy, since it saves one byte per line.
The unix ancestry of the C language carried this convention into the C language standard, which requires only “\n” (which encodes LF) to terminate lines, putting the burden on the runtime libraries to convert raw file data into logical lines.
The C language also introduced the term “newline” to express the concept of “generic line terminator”. I’m told that the ASCII committee changed the name of character 0x0A to “newline” around 1996, so the confusion level has been raised even higher.
Here’s another discussion of the subject, from a unix perspective
I've changed this second link to a snapshot in The Wayback Machine, since the actual page is not available anymore.
I hope this answers your question.
回答3:
It comes from the teletype machines (and typewriters) from the days of yore.
It used to be that when you were done typing a line, you had to move the typewriter's carriage (which held the paper and slid to the left as you typed) back to the start of the line (CR). You then had to advance the paper down a line (LF) to move to the next line.
There are cases you might not have wanted to linefeed when returning the carriage, such as if you were going to strikethrough a character with a dash (you'd just overwrite it).
But basically, it boils down to convention. DOS used the full CR/LF convention, and UNIX shortened it a bit. Now we're stuck!
回答4:
Others have given the answer, but I wanted to add... I guess you are too young to have used a typewriter? ;) The carriage is a drum. Moving it horizontally right, brings the stationary type head back to the left margin of the page. Rotating the carriage using your finger and thumb advances the page by one line(s).
回答5:
From Wikipedia:
The sequence CR+LF was in common use on many early computer systems that had adopted teletype machines, typically an ASR33, as a console device, because this sequence was required to position those printers at the start of a new line.
回答6:
I have seen more than one account to the effect that the reason to send two characters (and sometimes more) instead of one was in order to better match the data transfer rate to the physical printing rate (this was a long time ago). Moving the print-head took longer than printing a single character and sending extra characters was a way of preventing the data transfer from getting ahead of the printing device. So the reason we have multiple characters for end-of-line in Windows is basically the same as the reason we have QWERTY keyboards -- it was intended to slow things down.
Obviously the reason this practice continues in Windows to this day is based on some notion of ongoing backwards compatibility, and ultimately, just simple inertia.
Of note however, this convention is not strictly enforced by Windows at the operating system level. Any Windows application is free to ignore the convention, depending on what other applications it is trying to be compatible with.
Interestingly, the Wikipedia article about "Newline", claims that Windows 8 may introduce a change to using only LF. The article also states that Mac OS X introduced a transition from LF+CR to just LF.
来源：https://stackoverflow.com/questions/6521685/why-does-windows-use-cr-lf