LEX based Config Reader

lexer_config.flex

%{
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>

#include "config.h"

static struct config *cfg;
static unsigned char key[64], value[64];

static int inline getval(unsigned char *line)
{
	sscanf(line, "%s%s", key, value);
	return 0;
}

%}

%%
	/* Blank lines */
^[\ \t]*\n {}

	/* Comments */
^#.*\n {}

	/* IP Address */
ip_addr.*\n {
	getval(yytext);
	printf("IP address: %s\n", value);
	cfg->ip = inet_addr(value);
}

	/* Port */
port.*\n {
	getval(yytext);
	printf("Port: %s\n", value);
	cfg->port = atoi(value);
}

%%

int yywrap()
{
	return 1;
}

int parse_config(unsigned char *filename, struct config *config)
{
	if(NULL == (yyin = fopen(filename, "r")))
	{
		fprintf(stderr, "%s:%u %s failed to open configuration file %s\n", \
		   	__FILE__, __LINE__, __func__, filename);
		return -1;
	}

	printf("*** Parsing configuration file ***\n");
	cfg = config;
	yylex();
	printf("*** Done ***\n");

	return 0;
}

config.h

#ifndef CONFIG_H
#define CONFIG_H

struct config 
{
	unsigned int ip;
	unsigned int port;
};

#endif

config_main.c

#include <stdio.h>

#include "config.h"

int main()
{
	struct config cfg;

	if(0 != parse_config("example.cfg", &cfg))
		return -1;

	printf("After parsing\
			\n\tIP: %u\
			\n\tPort: %u\n", cfg.ip, cfg.port);

	return 0;
}

example.cfg

# example.cfg: Configuration file

# IP
ip_addr 10.172.17.1

# Port
port 21

# End of file

Makefile

all: ParseConfig

ParseConfig: config_main.c config.c
	gcc config_main.c config.c -o ParseConfig

config.c: config.l
	lex -o config.c config.l

clean:
	rm -vf config.c ParseConfig