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If everything in Unix development is POSIX, what the hell does C library do?

by jaywalker on 1/2/11, 3:03 PM with 22 comments

  • by tgflynn on 1/2/11, 6:01 PM

    There's something a bit strange about the approach of this post that suggests a confusion of concepts (though I'm not saying there's anything factually incorrect about it).

    The standard C library and the POSIX API are two quite different things.

    The standard C library is a library of functions defined by the various C language standards. These functions should be available on any C language implementation regardless of the platform (Unix/POSIX, Windows, embedded RTOS, micro-controller with no OS, etc.).

    The POSIX API is a platform specification for Unix like platforms (though the API is sometimes available non-natively on non-Unix like platforms). It is comparable to the win32 API on windows. It has no particular connection to the C language other than that C is the language in which the API is provided.

    Perhaps one reason for this confusion is that today many people are familiar with higher level programming environments like Java or Python which provide much richer standard libraries than do C and C++. They include things like multithreading and network communications. C programmers need to use platform specific API's like POSIX or win32 to access these services. Also note that pretty much any higher level language running on a modern OS is ultimately using the platform system API's to provide such services because the OS kernel doesn't allow user space programs access to them other than through a system call mechanism (which the platform API's typically wrap).

    One other possible source of confusion that the post doesn't mention is that on Unix the library one links to for both the C standard library functions and the Unix/POSIX system API's is called libc (it's usually called glibc on Linux). Despite the name this is not the same thing as the C standard library.

  • by tedunangst on 1/2/11, 3:50 PM

    Not sure where you got the idea that fork() isn't a system call. It certainly is on my computer.

    I think the overall sentiment is right on, but I'm not sure I get the last question. posix is a superset, yes, but it doesn't provide replacements for the C library. Perhaps better phrased as "Why limit yourself to only standard C?"?

  • by malkia on 1/2/11, 5:10 PM

    One example of good restriction to the "C" library is the lua reference implementation - because of that it can compile for lots of platforms (well 32-bit and above) without a problem.

    Another one is zlib, and lots of more.

  • by jdefr89 on 1/2/11, 5:56 PM

    I do not wish to be a troll but most of the information in that post is plain wrong. For one fork() is indeed a system call. If you want a good understanding of the true essence of POSIX (UNIX API) I recommend reading: Advanced Programming in the UNIX Environment.