Segmentation fault when parsing group elemnt with libconfig - c

Question

I'm trying to write C code to parse a config file using libconfig
The config file contains a simple element and a group. A group is composed of multiple settings, each has a unique name. ref
Config file :
host_name = "HOST";
device_settings:
{
rcu1:
{
product_id = 0x0001;
vendor_id = 0x0217;
},
rcu2:
{
product_id = 0x0001;
vendor_id = 0x0218;
}
}
I want to parse all RCUs data and store it in a data structre (the storing part is not a problem for now).
So I'm using the simple steps of :
Store the group in a config_setting_t * called section.
get length of section in a varaible called len
Iterrate len time to read RCUs data.
The problem is when i want to read RCU data i get a seg fault.
Code :
#include <libconfig.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
config_t cfg;
config_setting_t *root;
config_setting_t *section;
config_setting_t *elem;
int d, len;
config_init(&cfg);
if (config_read_file(&cfg,"./config.cfg") != CONFIG_TRUE) {
printf("[%s:%d] %s \n", config_error_file(&cfg),
config_error_line(&cfg), config_error_text(&cfg));
config_destroy(&cfg);
return -1;
}
if ((root = config_root_setting(&cfg)) == NULL) {
printf ("[%s:%d] %s \n", config_error_file(&cfg),
config_error_line(&cfg), config_error_text(&cfg));
config_destroy(&cfg);
return -1;
}
/* Device settings */
if ((section = config_setting_get_member(root, "device_settings")) != NULL)
{
len = config_setting_length(section);
printf("len = %d \n",len);
}
int i;
const char* device_id;
config_setting_t *device = NULL;
printf("device_settings %s a group \n",config_setting_is_group(section)?"is":"isn't");
for(i=0;i<len;i++) {
printf("iteration i = %d \n",i);
//device
if(device = config_setting_get_elem(section, i) != NULL) {
/*device id*/
if ((d = config_setting_lookup_string(device, "device_id",&device_id) != CONFIG_FALSE)) /*seg fault here*/
{
// Do stuff
}
}
}
return 0;
}
Something strange I noticed is when I compile the code i get this warning :
parse.c: In function ‘main’: parse.c:46:14: warning: assignment to
‘config_setting_t *’ {aka ‘struct config_setting_t *’} from ‘int’
makes pointer from integer without a cast [-Wint-conversion]
if(device = config_setting_get_elem(section, i) != NULL) {
GDB output :
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7da78a0 in config_setting_get_member () from
/lib/x86_64-linux-gnu/libconfig.so.9
ref to config_setting_get_elem(..)
I can not find what wrong Im doing. Everything looks correct to me.
Can someone see why the seg fault is happening?

Answer 1

if (device = config_setting_get_elem(section, i) != NULL)
needs to be
if ((device = config_setting_get_elem(section, i)) != NULL)
Because != has higher precedence than =.