Parse configuration files

introuble · 07-26-2006, 12:14 PM

My program needs to accept "settings" provided via a configuration file. The file must have the following properties:

#1. Lines beginning with "#" are considered comments.

#2. Empty lines are ignored. [A line filled with spaces = empty line too]

#3. Settings come in the form:

Code:

name=<value str>

<value str> can contain spaces.

Any known/recommended way to parse such a configuration file? Or should I just use fgets+strcmp etc.

ugenn · 07-26-2006, 12:17 PM

Get a good regex library, like pcre. If you can use C++, checkout boost::regex from the boost library.

introuble · 07-26-2006, 12:59 PM

I forgot to mention: Using C89

paulsm4 · 07-26-2006, 03:52 PM

My vote's for "fgets()"/"strcmp()".

If you find the solution inadequate, I'd worry first about making the data format more sophisticated (for example, going to XML instead of flat file) before I'd worry about a more sophisticated library.

But from everything you've said: a flat file sounds fine, and fgets()/strcmp() is the ideal way to parse that flat file.

IMHO .. PSM

xhi · 07-26-2006, 04:10 PM

Quote:

Originally Posted by paulsm4

My vote's for "fgets()"/"strcmp()".

If you find the solution inadequate, I'd worry first about making the data format more sophisticated (for example, going to XML instead of flat file) before I'd worry about a more sophisticated library.

But from everything you've said: a flat file sounds fine, and fgets()/strcmp() is the ideal way to parse that flat file.

IMHO .. PSM

yeh id agree.. regex would be nice but is a bit of an overkill.. you already know the format of the file, so it should not be too hard to write a small lib that parses that format..

ugenn · 07-26-2006, 09:22 PM

Quote:

Originally Posted by xhi

yeh id agree.. regex would be nice but is a bit of an overkill.. you already know the format of the file, so it should not be too hard to write a small lib that parses that format..

Unless the format is ridiculously simple, regex can not only aid in parsing the file, but also validate the token data, all in one fell swoop.

xhi · 07-27-2006, 09:04 AM

it looked pretty simple to me

name = value

not many swoops to that

ugenn · 07-27-2006, 09:19 AM

Quote:

Originally Posted by xhi

it looked pretty simple to me

name = value

not many swoops to that

And did you consider what acceptable values 'name' can hold? Apps written to be robust and secure will not just swallow whatever external data fed to it. This is where regex is handy.

xhi · 07-27-2006, 09:29 AM

im not disputing anything about regexs.. i am simply suggesting that if the configuration file is simple, then it will may be easier to implement your own parsing without regex..

do you have an example of using regexs easily with C89? i mean you suggested boost, and then came back with nothing helpful in the way of C89? i know regexes are great and i use them all the time, well that is when they are actually going to save me time..

ugenn · 07-27-2006, 09:32 AM

Quote:

Originally Posted by xhi

im not disputing anything about regexs.. i am simply suggesting that if the configuration file is simple, then it will may be easier to implement your own parsing without regex..

do you have an example of using regexs easily with C89? i mean you suggested boost, and then came back with nothing helpful in the way of C89? i know regexes are great and i use them all the time, well that is when they are actually going to save me time..

Read properly, I mentioned pcre. While not part of the std lib, it is widely ported on many platforms.

xhi · 07-27-2006, 10:03 AM

> Read properly

yes i did read that, i also mentioned easy, and worth the time to implement.. maybe it is easier to implement than i have seen, have any examples?

orhun · 07-27-2006, 02:03 PM

If C++ and boost is an option then I suggest boost.program_options library instead of boost.regex.

From boost.program_options documentation

Quote:

Introduction

The program_options library allows program developers to obtain program options, that is (name, value) pairs from the user, via conventional methods such as command line and config file.

Why would you use such a library, and why is it better than parsing your command line by straightforward hand-written code?

* It's easier. The syntax for declaring options is simple, and the library itself is small. Things like conversion of option values to desired type and storing into program variables are handled automatically.
* Error reporting is better. All the problems with the command line are reported, while hand-written code can just misparse the input. In addition, the usage message can be automatically generated, to avoid falling out of sync with the real list of options.
* Options can be read from anywhere. Sooner or later the command line will be not enough for your users, and you'll want config files or maybe even environment variables. These can be added without significant effort on your part.

xhi · 07-27-2006, 02:13 PM

nice. i had never heard of that. i dont know if that is an option for OP but thats good info either way.

ugenn · 07-27-2006, 11:49 PM

For pcre, look at pcredemo.c in the pcre source. Essentially, it's just 2 functions, pcre_compile and pcre_exec.

jineshkj · 09-01-2006, 01:10 AM

Quote:

Originally Posted by introuble

My program needs to accept "settings" provided via a configuration file. The file must have the following properties:

#1. Lines beginning with "#" are considered comments.

#2. Empty lines are ignored. [A line filled with spaces = empty line too]

#3. Settings come in the form:

Code:

name=<value str>

<value str> can contain spaces.

Any known/recommended way to parse such a configuration file? Or should I just use fgets+strcmp etc.

I'm sorry that I've made this reply so lately. You can try the following:

http://sourceforge.net/projects/parser