Reading config file in C using libconfig

Question

I defined a structure for options in my config file and a pointer to this structure in "config.h" file and I read config file using libconfig and set values in function get_config() that is defined in file "config.c". In main function I initialize pointer to structure and call get_config() function. libconfig works well and prints values of structure's fields correctly but when I print same fields in main functions their values are incorrect!

"config.h"

#include <stdio.h>
#include <stdlib.h>
#include <libconfig.h>

typedef struct
{
    int buffer_size;
    const char * DBusername;
    const char * DBpassword;
}conf;

conf *config;

int get_config();

"config.c"

#include "config.h"


int get_config()
{
    config_t cfg;
    config_setting_t *setting;

    config_init(&cfg);

    /* Read the file. If there is an error, report it and exit. */
    if(! config_read_file(&cfg, "config.cfg"))
    {
        fprintf(stderr, "%s:%d - %s\n", config_error_file(&cfg),
            config_error_line(&cfg), config_error_text(&cfg));
        config_destroy(&cfg);
        return(EXIT_FAILURE);
    }

    if(config_lookup_int(&cfg, "buffersize", &config->buffer_size))
        printf("buffersize: %d\n\n", config->buffer_size);
    else
        fprintf(stderr, "No 'buffersize' setting in configuration file.\n");

    if(config_lookup_string(&cfg, "DBusername", &config->DBusername))
        printf("DBusername: %s\n\n", config->DBusername);
    else
        fprintf(stderr, "No 'DBusername' setting in configuration file.\n");

    if(config_lookup_string(&cfg, "DBpassword", &config->DBpassword))
        printf("DBpassword: %s\n\n", config->DBpassword);
    else
        fprintf(stderr, "No 'DBpassword' setting in configuration file.\n");

    config_destroy(&cfg);

    return(EXIT_SUCCESS);

}

"store.c"

int main(){
    config = (conf*) malloc(sizeof(conf));
    if(get_config() == EXIT_FAILURE)
        return 0;

    printf("\n%s", config->DBusername);
    printf("\n%s", config->DBpassword);
    printf("\n%d", config->buffer_size);
}

Answer 1

The problem is because of defining char* in structure. I changed the char* to char[] and the problem is solved! :)

Answer 2

I defined a structure for options in my config file and a pointer to this structure in "config.h" file...

That statement makes me wonder what a config file is. i.e. is it a .c, or a .h? And what is the visibility to it for other files?

Your issue is likely because the scope (visibilty) of the structure is not provided to the file in which the main() function resides. #include the .h where the struct is defined, and make sure an instantiation of that struct either has global scope, or create an instantiation inside main()

This configuration of files will provide visibility to to main of a struct defined in the .h:

in somefile.h:

typedef struct 
{
  int membername;
} A_STRUCT;

extern A_STRUCT a

;

in someotherFile.c

#include "somefile.h"

A_STRUCT a = {3};  //global copy of the struct, with assignment

int main(void)
{
    printf("%d", a.membername);
    return 0;
}