File based configuration handling in C (Unix)

Question

This is probably one of the most common tasks / problems when programming; You need to store the configuration of your application somewhere.

While I'm trying to create a webserver or other applications, I'd like to keep the code as clean as possible since my main interest in programming is architecture. This results in me wanting to store configurations in a file which can be changed without having to re-compile the software.

I'm not here to re-invent the wheel or anything like that, so what I'd like to do is creating a Configuration reader in C on *nix. The configuration might look a lot like any other software's configuration; Apache, vsftpd, MySQL, etc.

The basic question is: How do you read from a textfile and process each line efficiently (in pure C)? Do I need to use fgetc() and process each char?

Answer 1

Hmmm there is LibConfig.

I have found it in Wiki

Answer 2

Various people have given reasonably good advice - the Pure-FTP example is interesting.

You should also read TAOUP (The Art of Unix Programming) by E S Raymond. It has examples a-plenty of configuration files. It also outlines canonical idioms for the configuration files. For example, you should probably allow '#' to start a comment to the end of the line, and ignore blank lines. You should also decide what you will do if the configuration file contains a line you don't understand - whether to ignore and continue silently, or whether to complain. (I prefer things that complain; then I know why what I've just added isn't having any effect - whereas silent ignoring means I don't know whether the entry I just added has any effect.)

Another problem is locating the configuration file. Do you do that by compiled-in location, by a default install location with environment variable to override, or by some other piece of magic? Make sure there's a command line option to allow the configuration file to be specified absolutely - even consider making that the only way to do it.

Otherwise, within broad limits, keep it simple and everyone will be happier.