streams - text stream
Hi, I am learning about streams and I/O, and my book says that with text streams some character translations can take place. ie - the newline character may be converted into a carriage return linefeed sequence. I was not sure what the carriage return linefeed sequence was, and when I searched it, it seems to just be the same as a newline character (/n) but with more characters, i believe a /r too? So I am wondering the difference, and also why would this conversion take place. My book does not explain it, simply says that it happens.
It happens because different Operating Systems use different line endings. For example Windows uses the "\r\n" sequence, while Linux uses the "\n" sequence.
CR/LF codes are an anachronism. The first terminals were teletype machines evolved from manually-operated typewriters. They printed results on actual paper.
On a typewriter, a carriage carrying a spool of paper moves from right-to-left across the print head as keys are depressed. When the carriage moves fully to the left, the user must unroll a little more paper and physically push the carriage to the right. See:
https://www.youtube.com/watch?v=EiyZSX0OnBM
Very old teletypes were essentially electronic typewriters. The computer communicated with the user by typing, and would feed the line or return the carriage only when a line-feed (LF) or carriage-return (CR) code was sent over the wire.
https://www.youtube.com/watch?v=S81GyMKH7zw
Later systems retained the separation between LF and CR for compatibility reasons.
So that's why LF and CR exist. They're important today because '\n' is a notation introduced by C: there is no new-line character in ASCII. Therefore, the standard library must translate '\n' into the sequence of bytes which best represents "newline" on the system.
Microsoft Windows represents a new-line in bytes by a carriage return code followed by a line feed, while Unix typically uses only one line feed. Old Mac programs used only a carriage return, but now Mac has joined with Unix.
Therefore, when you say
text_file << '\n';
It tells the C++ library "I want a newline", and the C++ library does whatever it needs to do to make sure that the bytes in text_file represent a new line.
On a typewriter, a carriage carrying a spool of paper moves from right-to-left across the print head as keys are depressed. When the carriage moves fully to the left, the user must unroll a little more paper and physically push the carriage to the right. See:
https://www.youtube.com/watch?v=EiyZSX0OnBM
Very old teletypes were essentially electronic typewriters. The computer communicated with the user by typing, and would feed the line or return the carriage only when a line-feed (LF) or carriage-return (CR) code was sent over the wire.
https://www.youtube.com/watch?v=S81GyMKH7zw
Later systems retained the separation between LF and CR for compatibility reasons.
So that's why LF and CR exist. They're important today because '\n' is a notation introduced by C: there is no new-line character in ASCII. Therefore, the standard library must translate '\n' into the sequence of bytes which best represents "newline" on the system.
Microsoft Windows represents a new-line in bytes by a carriage return code followed by a line feed, while Unix typically uses only one line feed. Old Mac programs used only a carriage return, but now Mac has joined with Unix.
Therefore, when you say
text_file << '\n';
It tells the C++ library "I want a newline", and the C++ library does whatever it needs to do to make sure that the bytes in text_file represent a new line.
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