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Old 03-20-2017, 06:00 AM   #1
yakkmeister
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Registered: Jan 2005
Location: QLD Australia
Distribution: Ubuntu LTS 14.04
Posts: 56

Rep: Reputation: 15
C - Adding n nodes to a slist with struct - glib


Hello,

I'm trying to wrap my head around using glib for its list and sorting routines, in the hope that I'd be doing myself a favour in using robust code ...

I discovered that I have 2 big problems here, one of which there may be no solution to.

What I need to do is create n nodes, insert them into the list, calculate a number then sort them based on the number.

I recognised that I would need a struct for the node data as GSList only has a single pointer and single variable.
GSList

Problem is, each struct would need to be named, so I expect that I would need to have anticipated every name ... which means I don't really think I'm approaching the problem correctly ... I suspect there may be no direct remedy for this.

Second, I get an error at compile-time - it complains that it expected GCompareFunc but got something like GInt.
I do apologise for not having the exact error - I'll paste it when I get to work tomorrow (my home machine doesn't like to locate any libs at all so I can't reproduce it... :/ )
Suffice to say, I don't get what it wants in terms of being a GCompareFunc.



Details:

I have been using this IBM tutorial on data management with Glib.

Eventually, I want to be able to read a series of numbers from a file (probably a .csv) then add that number of new items to my list.
The random number simply pretends to be the number from a file.

The following code is, clearly, broken... but maybe it'll help explain what I'm trying to achieve.
I've attempted writing my own lists, I was using a doubly linked list of Struct with next* and prev* pointers in there but I couldn't get it to work - I know, shame on me...

Code:
//lists.c
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <string.h>
#include <glib.h>

typedef struct {
	int id;
	int iq;
} Person;

gint my_comparator(gconstpointer item1, gconstpointer item2) {
	return item1 - item2;
}

int main(int argc, char** argv) {
	GSList* list = NULL;
	
	int i;

	srand(time(NULL)); //random number takes the place of file input for now

	for(i = (rand() % 100); i > 0; i--){
		Person* !problem! = g_new(Person, 1); 		// allocate memory for one Person struct
		!problem!->id = i;				// !problem! = here's the problem
		!problem!->iq = (rand() % 200);
		list = g_slist_prepend(list, !problem!); 	//prepend for speed
	}
	list = g_slist_sort(list, (GCompareFunc)my_comparator);	//something really wrong here

	return 0;
}

Last edited by yakkmeister; 03-20-2017 at 06:46 AM. Reason: mucked up the code!
 
Old 03-20-2017, 07:45 AM   #2
yakkmeister
Member
 
Registered: Jan 2005
Location: QLD Australia
Distribution: Ubuntu LTS 14.04
Posts: 56

Original Poster
Rep: Reputation: 15
Problem solved.

A friend of mine (in Germany, no less) happened to come online and help me out. I wasn't as far off as I thought I was ...
Here's the working code:

Code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <string.h>
#include <glib.h>

typedef struct {
    int id;
    int iq;
} Person;

gint my_comparator(gconstpointer item1, gconstpointer item2)
{
    return ((Person*)item1)->iq - ((Person*)item2)->iq;
}

int main(int argc, char** argv)
{
    GSList* list = NULL;

    int i;

    srand(time(NULL)); //random number takes the place of file input for now

    for(i = (rand() % 100); i > 0; i--){
        Person* problem = g_new(Person, 1);         // allocate memory for one Person struct
        problem->id = i;
        problem->iq = (rand() % 200);
        list = g_slist_prepend(list, problem);  //prepend for speed
    }
    list = g_slist_sort(list, (GCompareFunc)my_comparator); //something really wrong here
    for(GSList *p = list; p; p = p->next)
        printf("%d: %d\n", ((Person*)p->data)->id, ((Person*)p->data)->iq);

    return 0;
}
 
  


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