Thread: question on function pointers

Hello I have another question this one regards function pointers.
I have an api function that has the following prototype.

Code:

int sqlite3_exec( 
  sqlite3*,                                  /* An open database */
  const char *sql,                           /* SQL to be evaluated */
  int (*callback)(void*,int,char**,char**),  /* Callback function */
  void *,                                    /* 1st argument to callback*/
  char **errmsg                              /* Error msg written here */
);

the callback function takes a void pointer for the argument and returns
an integer used for sqlite return code.


I need to be able to return values from the callback function however I
am not sure how I can do that. I have heard that u can pass a function
pointer as the argument to be able to this but I am not sure how this is
done.
If anyone can help me with this I would be greatful. I have spent a long
time trying to figure this out on my own I have to go sleep now.


thank you.

I understand this, my question is that since the callback function returns an integer and I need to retrieve a struct from it, how can I do this? So basically is there a way I can pass a pointer as argument where I can save my values and be able to retrieve them from the pointer outside of the function? the argument takes a void pointer so I will have to cast it and assign it to another variable. I assume defining a global variable pointer to a struct will work but not sure.

Code:

static struct test *arg;

int main()
{
   struct test *q;
   q = malloc(sizeof(struct test));
   /* allocate memory for any further values needed for struct */
   sqlite3_exec(sqlite, sqlstmt, my_callback, &q, &error);
}

int my_callback(void *ptr1, int num, char **ptr2, char **ptr3)
{
   arg = (struct test *)ptr1;
   /* update arg values */
}

I have not tried this yet but I assume it should do the job if you have any suggestions please let me know.