Config File Parser

This archive is about how to use Flex and Bison (Yacc) to parse config files that is self-defined. The contens is shown below:

Description File Design

Key-Values

Format of the config file is similar to JSON, which is composed of pairs of key-values. The config file is also composed of some tuples, which contain some pairs of key-values. e.g.

section {
 key1 = "string";
 key2 = 12.34;
}

Therefore,

section.key1= "string"
section.key2=12.34

Inheritance Mechanism

Besides the features above, the config file also supports inheritance mechanism. The symbol of inheritance is shown by ":", e.g.

derived_section : section {
  key1 = "override string";
  key3 = 10;
}

Therefore,

derived_section.key1="override string"
derived_section.key2=12.34
derived_section.key3=10

The types of the config file include int, float, string.

Induction Mechanism

The config file also introduces induction mechanism, which is expressed by "include", e.g.
The contents of a.config:

section_a {
 key1 = "string";
 key2 = 12.34;
}

The contents of b.config:

#include "path/a.config"
section_b {
 key1 = "str1";
 key2 = 12.34;
x {
 key1=2;
 key2=8;
}
y : section_b.x {
 key1=20;
 key3=33;
}
}
z:section_a {
key1="str";
key2=25;
}

Comments

The config file also supports comments, formularized by /comments/ or //, e.g.

//comment
section {
 key1 = /* comment*/ "string";
 key2 = 12.34;
}

Syntax Design

To parse the config file, flex & bison is of much efficiency. Before using the mature tools, we have to define the grammar in advance, which is formularized by Backus-Naur Form. The config files' Backus-Naur Form is shown below:

tuples::= tuple tuples | \epsilon
tuples::= ID LB entries RB | ID COLON LB entries RB
entries::= kv entries | tuple entries | \epsilon
kv::= ID EQ value END
value::= FLOAT | INT | ctring | NULLV
cstring::= STRING cstring

INT->[0-9]+
FLOAT->[+-]?[0-9]+(\.[0-9]*)?
STRING->\"(\\.|[^\\"])*\"
ID->[a-z_][a-z0-9_\.]*
LB->{
RB->}
COLON->:
EQ->=
END->;
NULLV->NULL

Usage

To Compile the source code, you need to install git & make. You can use the following command line to complie them:

$ git clone https://github.com/lijiansong/ConfigFileParser
$ cd ConfigFileParser
$ make

After the above cmds, you would get an executable file, named config_parser, and a static library suffixed by .a, named lib_cfg_parser.a. You can execute it like this( before use it you need to write a config file that is formulized by the grammar defined above ):

$ ./config_parser test.config

You can also call the static library lib_cfg_parser.a in your own program.
To learn more...

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