When using system-level IO in Linux, I noticed that the compiler recognized the O_RDONLY and O_RDWR flags, but it had no clue whatsoever as to the meaning of the O_BINARY and O_TEXT flags.
Is this a Linux thing?
No O_BINARY and O_TEXT flags in Linux?
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5 Answers
Linux, and just about every flavor of Unix for that matter, doesn't differentiate between binary and text files. Thus, there are no standard constants with that name. You can manually define the constants to be zero in Linux if you want to include them in your code for portability purposes.
http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2007-03/msg00147.html
It's a *nix thing. *nix operating systems don't do automatic linefeed conversion for I/O on "text" files so O_TEXT and O_BINARY flags wouldn't make sense.
At the level of C language and its standard library, there's no such thing as O_BINARY and O_TEXT flags. The binary or text mode is selected by adding the b specifier of the mode parameter of fopen function. The specifier itself is, of course, supported by all C implementations, but on POSIX platforms this specifier has no effect: per POSIX specification the text mode is the same as the binary mode.
Not suprisingly, if you dig deeper into the level of non-standard platform-specific Unix I/O functions, you'll discover that they have no knowledge of that text/binary distinction whatsoever.
Windows uses \r\n for line endings, Linux (and other Unix-alikes) use just \n. In Windows, reading O_BINARY gives you the raw data, possibly odd line endings and all, while O_TEXT normalises the line endings, so your C code only sees a single character.
Under Linux et al, there's no point distinguishing between text and binary, because the data only has a single character anyway, so the flags are unnecessary.
There isn't a difference at the OS level between binary and text file under Unix. Text file have just a restricted content. That's also true for Windows, but the conventions used by C for the end of lines are the same as the one used by Unix, while Windows use CR/LF pair (and an explicit end of file marker in some contexts, but the handling of that was not consistent even in the system programs last time I checked), so a mapping is needed to respect the conventions mandated by C.
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