do you the type of this variable?

MounaRM · 11-25-2013, 10:15 AM

hello everyone, I wrote this code, and I am having a big problem to manipulate it:

Code:

 
struct neighbor {
 	int id;
	float ph;
	struct neighbor * next;
};
typedef struct neighbor T_neighbor;
//========================================================
struct entree {
	int destination_id;
	T_neighbor  * neighbor;
	struct entree * next;
};
typedef struct entree T_entree;
 
 
 
//========data 
struct data {
	//
	T_entree *		table;
 
};typedef struct data T_data;

whenever I try to use data->table , I got a segmentation fault.I think the type of data->table is T_entree * . Have you any idea about the type of data->table ?
thanks in advance for the help.

NevemTeve · 11-25-2013, 10:32 AM

1. simplify it:

Code:

 
typedef struct neighbor {
        int id;
        float ph;
	struct neighbor * next;
} neighbor;

typedef struct entree {
	int destination_id;
	neighbor  * neighbor;
	struct entree * next;
} entree;

typedef struct data {
	entree *table;
} data;

2. Compile with flags -W -Wall -Wextra -Werror

3. Always initialize your pointers with NULL, structures with memset, eg:

Code:

entree e1;
memset (&e1, 0, sizeof (e1));

4. Use debugger

5. Quote the problematic code

mina86 · 11-25-2013, 10:40 AM

Problem is with the place you are using this data structure. Not here where it is defined. Provide a short example code where the undesired behaviour can be tested, and then someone might be able to help.

MounaRM · 11-25-2013, 03:18 PM

Quote:

Originally Posted by mina86

Problem is with the place you are using this data structure. Not here where it is defined. Provide a short example code where the undesired behaviour can be tested, and then someone might be able to help.

I wanted to add contents to data->table, so I defined a function :

Code:

void AddDestination(T_entree **pp_L,int id){
	T_entree *nouveau;
	nouveau=(T_entree*)malloc(sizeof(T_entree));
	nouveau->destination_id=id;
	nouveau->neighbor=NULL;
	nouveau->next=*pp_L;
	*pp_L=nouveau;
}

in order to test this function, I added this code to main()

Code:

T_entree *L;
L=NULL;
AddDestination(&L,3);

this code works correctly , but when I tried the same test with data->table in stead of L , it didn't work !

Code:

T_data * data = malloc(sizeof(T_data));
AddDestination(&data->table,3);

may be I should initialize table, but I have no idea how to do it ..
Any idea ?
thanks

mina86 · 11-25-2013, 03:44 PM

Code:

nouveau=(T_entree*)malloc(sizeof(T_entree));

Don't do that. In C the cast is unnecessary and at times may lead to compiler silently ignoring stdlib.h not being included. Furthermore, I would recommend using of the variable rather then the type with sizeof, as in:

Code:

nouveau = malloc(sizeof *nouveau);

As to your problem, the below works just fine:

Code:

#include <stdlib.h>

typedef struct neighbor {
	int id;
	float ph;
	struct neighbor *next;
} T_neighbor;

typedef struct entree {
	int destination_id;
	T_neighbor  *neighbor;
	struct entree *next;
} T_entree;

typedef struct data {
	T_entree *table;
} T_data;

void AddDestination(T_entree **pp_L,int id){
	T_entree *nouveau;
	nouveau = malloc(sizeof *nouveau);
	nouveau->destination_id = id;
	nouveau->neighbor = NULL;
	nouveau->next = *pp_L;
	*pp_L = nouveau;
}

int main(void) {
	T_entree *L;
	T_data *data;

	AddDestination(&L, 3);

	data = malloc(sizeof *data);
	AddDestination(&data->table, 3);

	return 0;
}

So again, please provide a complete minimal code where we can observe the issue you are experiencing.