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-   -   Difference between '\n' and '\r\n' ... (http://www.go4expert.com/articles/difference-n-rn-t8021/)

Bhullarz 29Dec2007 08:17

Difference between '\n' and '\r\n' ...
 
I recently faced a problem regarding these 2 Escape Sequences. So, I thought I should share the difference between these two to clarify to all who may hay have confusion like me.

Thanks to Shabbir too......

The Difference



There are a few characters which can indicate a new line. The usual ones are these two:
* '\n' or '0x0A' (10 in decimal) -> This character is called "Line Feed" (LF).
* '\r' or '0x0D' (13 in decimal) -> This one is called "Carriage return" (CR).
Different Operating Systems handle newlines in a different way. Here is a short list of the most common ones:
* DOS and Windows
They expect a newline to be the combination of two characters, namely '\r\n' (or 13 followed by 10).
* Unix (and hence Linux as well)
Unix uses a single '\n' to indicate a new line.
* Mac
Macs use a single '\r'.

This difference gives rise to a number of problems. For example, a file created under Unix (so with newlines as a single LF) will not open correctly under Window's Notepad. Any Windows program that expects newlines to be CRLF will not work correctly with these files.

To unify things a bit, so that writing portable C/C++ programs is possible, file streams have both a "translated" and an "untranslated" mode. If you open a file in translated mode, the runtime library will convert a '\n' to the appropriate newline character(s). If the following program is compiled under Unix, the file will contain a single LF to indicate the newline. If it's compiled under windows, it will contain a CRLF.

Code:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *fp = fopen("testfile.txt", "w");
    fprintf(fp, "Hello World\n");
    fclose(fp);
    return 0;
}

If you look at the generated file with a hex editor, you will see that the windows version has generated the following:
Code:

H    e    l    l    o        W    o    r    l    d  CR  LF
0x48 0x65 0x6C 0x6C 0x6F 0x20 0x57 0x6F 0x72 0x6C 0x64 0x0D 0x0A

So file streams are handled in a transparent way, provided of course that you only handle files compatible with your operating system. But many times you have to pass multi-line strings directly to some system functions.

In practice

In Windows you have to pass multi-line strings with '\r\n', otherwise the system functions don't recognize them correctly as multi-line. This is true e.g. for setting the text of Edit controls, Labels, Windows etc. Also, when you read multi-line text from a file that initially contains '\r\n' in translated mode, the string in memory will contain only a single '\n'. See for example the documentation on MSDN about 'fread()':
Quote:

Originally Posted by MSDN
The fread function reads up to count items of size bytes from the input stream and stores them in buffer. The file pointer associated with stream (if there is one) is increased by the number of bytes actually read. If the given stream is opened in text mode, carriage return–linefeed pairs are replaced with single linefeed characters. The replacement has no effect on the file pointer or the return value. The file-pointer position is indeterminate if an error occurs. The value of a partially read item cannot be determined.

If you want to be able to read text files written on different operating systems, you have to open the file in binary (= untranslated) mode and check for the different newlines yourself.

shabbir 29Dec2007 10:04

Re: Difference between '\n' and '\r\n ...
 
Nicely explained.

pradeep 29Dec2007 12:11

Re: Difference between '\n' and '\r\n' ...
 
Nice article. You can use EditPlus opens all types of files, it automatically detects line endings!

shabbir 29Dec2007 13:41

Re: Difference between '\n' and '\r\n' ...
 
Quote:

Originally Posted by pradeep
Nice article. You can use EditPlus opens all types of files, it automatically detects line endings!

Thats when using the editor but you should also know which OS does what newline characters

shabbir 1Jan2008 20:18

Re: Difference between '\n' and '\r\n' ...
 
I have reported the article for Nominate your favorite article of the month for December 2007. Add your nominations as well.

asadullah.ansari 11Jan2008 10:23

Re: Difference between '\n' and '\r\n' ...
 
Very nice !!! Thanks for this kind of info!!!

shabbir 20Jan2008 23:13

Re: Difference between '\n' and '\r\n' ...
 
Vote this article for Article of the month for December 2007


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