very weird problem (pointers I think)

I have a very weird problem with a piece of code I've written. I have been searching and debugging for three days now, and I still haven't found it. Unfortunately, I don't known where exactly the error is located (I know it is in area.c, but not which function etc...). So I don't really expect that you will look at it for a while, and eventually find it, but I still hope so. This is the problem :

- these are the most important structures used in the code
(coordinates are stored relatively : from 0 -> 1)

Code:

---

typedef struct Area{
        struct Area *prev, *next;

        int handle;

        struct AreaEdge *top;
        struct AreaEdge *left;
        struct AreaEdge *bottom;
        struct AreaEdge *right;
}Area;

//things to know :
//area1 : upper or left area
//area2 : down or right area
//point1 : upper or left areaPoint
//point2 : down or right areaPoint
typedef struct AreaEdge{
        struct AreaEdge *prev, *next;

        struct Area *area1;
        struct Area *area2;
        struct AreaPoint *point1;
        struct AreaPoint *point2;

        int direction;
}AreaEdge;

#define GUI_HORIZONTAL        0
#define GUI_VERTICAL        1

typedef struct AreaPoint{
        struct AreaPoint *prev, *next;

        float x;
        float y;
}AreaPoint;

---

- first of all : during initialisation, this is called :

Code:

---

addDefaultArea(s);
(see last block of code)

---

- situation : I have a default area
4 areaPoints, 4 areaEdges and 1 area (linked to eachother well)

- I made a splitArea funtion which splits the area where the usere clicks with the left mouse button :
(ev->val1 and ev->val2 are the coordinates of the mouseclick)

Code:

---

case GUI_MOUSE_LEFT_DOWN:
                if (ae = onAreaEdge(ev->val1, ev->val2)){
                        splitAreaWhere(ae, ev->val1, ev->val2);
                        return 0;
                }
                else return 1;

---

- I'll copy area.c here.

Code:

---

//area
Area *initArea(){
        Area *a;

        a = malloc(sizeof(Area));

        a->next = 0;
        a->prev = 0;
        a->top = a->bottom = a->left = a->right = 0;
        a->handle = 0;

        return a;
}

Area *addArea(Screen *s, AreaEdge *e1, AreaEdge *e2){
        Area *a;
        AreaEdge *top, *left, *bottom, *right;

        if (!s) return 0;
        if (!e1 || !e2) return 0;
        if (e1->direction != e2->direction) return 0;

        a = initArea();
        LIST_append(s->area, a);

        a->handle = (int)a;

        if (e1->direction == GUI_HORIZONTAL){
                if(e1->point1->y > e2->point1->y){
                        bottom = e1;
                        top = e2;
                }
                else{
                        bottom = e2;
                        top = e1;
                }
                if ( !(left = getAreaEdge(s, top->point1, bottom->point1)) )
                        left = addAreaEdge(s, top->point1, bottom->point1);
                if ( !(right = getAreaEdge(s, top->point2, bottom->point2)) )
                        right = addAreaEdge(s, top->point2, bottom->point2);
        }
        else{
                if(e1->point1->x > e2->point1->x){
                        right = e1;
                        left = e2;
                }
                else{
                        right = e2;
                        left = e1;
                }
                if ( !(top = getAreaEdge(s, left->point1, right->point1)) )
                        top = addAreaEdge(s, left->point1, right->point1);
                if ( !(bottom = getAreaEdge(s, left->point2, right->point2)) )
                        bottom = addAreaEdge(s, left->point2, right->point2);
        }

        a->top = top;
        top->area2 = a;
        a->left = left;
        left->area2 = a;
        a->bottom = bottom;
        bottom->area1 = a;
        a->right = right;
        right->area1 = a;

        return a;
}

void removeArea(Screen *s, Area *a){
        int index;

        index = LIST_getElemIndex(s->area, a);
        LIST_removeAt(s->area, index);

        if (a == a->top->area2) a->top->area2 = 0;
        if (a == a->bottom->area1) a->bottom->area1 = 0;
        if (a == a->left->area2) a->left->area2 = 0;
        if (a == a->right->area1) a->right->area1 = 0;

        a->handle = 0;

        freeArea(a);
}

void freeAreaList(List *l){
        Area *a;

        while(l->first){
                a = LIST_removeLast(l);
                freeArea(a);
        }
}

void freeArea(Area *a){
        free(a);
}

//areaEdge
AreaEdge *initAreaEdge(){
        AreaEdge *ae;

        ae = malloc(sizeof(AreaEdge));

        ae->next = 0;
        ae->prev = 0;

        ae->point1 = 0;
        ae->point2 = 0;

        ae->area1 = 0;
        ae->area2 = 0;

        ae->direction = -1;

        return ae;
}

AreaEdge *addAreaEdge(Screen *s, AreaPoint *p1, AreaPoint *p2){
        AreaEdge *a;
        int dir=0;

        if (!s) return 0;
        if (!p1 || !p2) return 0;

        if ( (p2->x - p1->x) > 0.0001f ) dir |= 1;
        if ( (p2->y - p1->y) > 0.0001f ) dir |= 2;
        if (dir == 0 || dir == 3) return 0;
        dir--;

        a = initAreaEdge();
        LIST_append(s->areaEdge, a);

        a->point1 = p1;
        a->point2 = p2;
        a->direction = dir;

        return a;
}

void removeAreaEdge(Screen *s, AreaEdge *ae){
        int index;

        if (ae->area1 || ae->area2) return;

        index = LIST_getElemIndex(s->areaEdge, ae);
        LIST_removeAt(s->areaEdge, index);

        ae->point1 = 0;
        ae->point2 = 0;
        ae->direction = -1;

        freeAreaEdge(ae);
}

void freeAreaEdgeList(List *l){
        AreaEdge *ae;

        while(l->first){
                ae = LIST_removeLast(l);
                freeAreaEdge(ae);
        }
}

void freeAreaEdge(AreaEdge *ae){
        free(ae);
}

AreaEdge *getAreaEdge(Screen *s, AreaPoint *p1, AreaPoint *p2){
        AreaEdge *t;

        t = s->areaEdge->first;
        while(t){
                if (t->point1 == p1 && t->point2 == p2){
                        return t;
                }
                else if (t->point1 == p2 && t->point2 == p1){
                        return t;
                }
                t = t->next;
        }
        return 0;
}

//areaPoint
AreaPoint *initAreaPoint(){
        AreaPoint *ap;

        ap = malloc(sizeof(AreaPoint));

        ap->next = 0;
        ap->prev = 0;

        ap->x = 0;
        ap->y = 0;

        return ap;
}

AreaPoint *addAreaPoint(Screen *s, float x, float y){
        AreaPoint *p;

        if (!s) return 0;

        p = initAreaPoint();
        LIST_append(s->areaPoint, p);

        p->x = x;
        p->y = y;

        return p;
}

void removeAreaPoint(Screen *s, AreaPoint *ap){
        AreaEdge *t;
        int index;

        t = s->areaEdge->first;
        while(t){
                if (t->point1 == ap || t->point2 == ap) return;
                t = t->next;
        }

        index = LIST_getElemIndex(s->areaPoint, ap);
        LIST_removeAt(s->areaPoint, index);

        ap->x = 0;
        ap->y = 0;

        freeAreaPoint(ap);
}

void freeAreaPointList(List *l){
        AreaPoint *ae;

        while(l->first){
                ae = LIST_removeLast(l);
                freeAreaPoint(ae);
        }
}

void freeAreaPoint(AreaPoint *ap){
        free(ap);
}

void addDefaultArea(Screen *s){
        AreaPoint *p1, *p2, *p3, *p4;
        AreaEdge *e1, *e2, *e3, *e4;
        Area *a;
        float x, y;

        x = 0;        y = 0;
        p1 = addAreaPoint(s, x, y);
        x = 1;        y = 0;
        p2 = addAreaPoint(s, x, y);
        x = 1;        y = 1;
        p3 = addAreaPoint(s, x, y);
        x = 0;        y = 1;
        p4 = addAreaPoint(s, x, y);

        e1 = addAreaEdge(s, p1, p2);
        e2 = addAreaEdge(s, p2, p3);
        e3 = addAreaEdge(s, p4, p3);
        e4 = addAreaEdge(s, p1, p4);

        a = addArea(s, e1, e3);
}

void splitAreaWhere(AreaEdge *ae, int x, int y){
        AreaPoint *lb, *rb, *ro, *lo, *newp1, *newp2;
        AreaEdge *b, *o, *l, *r, *newe1, *newe2, *newe3, *newe4, *newe5;
        Area *split = 0, *newa1, *newa2;
        guiEvent *event = 0;
        float fx, fy, where;
        int dir, loop_done = 0;

        //1 : omzetten naar relatieve coordinaten
        fx = (float)x / (float)G->win->x;
        fy = (float)y / (float)G->win->y;

        dir = ae->direction;
       
        //2 : berekenen welke area
        if (dir == GUI_HORIZONTAL){
                where = fx;
                if (fy >= ae->point1->y) split = ae->area2;
                else split = ae->area1;
        }
        else{
                where = fy;
                if (fx >= ae->point1->x) split = ae->area2;
                else split = ae->area1;
        }

        printf("split : %d\n", split);
        printf("ae : %d\n", ae);

        lb = split->top->point1;
        rb = split->top->point2;
        ro = split->bottom->point2;
        lo = split->bottom->point1;

        b = split->top;
        o = split->bottom;
        l = split->left;
        r = split->right;

        //3 : de eigenlijke splitsing
        if (dir == GUI_HORIZONTAL){
                removeArea(G->curScreen, split);

                removeAreaEdge(G->curScreen, b);
                removeAreaEdge(G->curScreen, o);

                newp1 = addAreaPoint(G->curScreen, where, l->point1->y);
                newp2 = addAreaPoint(G->curScreen, where, l->point2->y);

                newe1 = addAreaEdge(G->curScreen, lb, newp1);
                newe2 = addAreaEdge(G->curScreen, newp1, rb);
                newe3 = addAreaEdge(G->curScreen, lo, newp2);
                newe4 = addAreaEdge(G->curScreen, newp2, ro);
                newe5 = addAreaEdge(G->curScreen, newp1, newp2);

                newa1 = addArea(G->curScreen, newe1, newe3);
                newa2 = addArea(G->curScreen, newe2, newe4);
        }
        else{
                removeArea(G->curScreen, split);

                removeAreaEdge(G->curScreen, l);
                removeAreaEdge(G->curScreen, r);

                newp1 = addAreaPoint(G->curScreen, b->point1->x, where);
                newp2 = addAreaPoint(G->curScreen, b->point2->x, where);

                newe1 = addAreaEdge(G->curScreen, lb, newp1);
                newe2 = addAreaEdge(G->curScreen, newp1, lo);
                newe3 = addAreaEdge(G->curScreen, rb, newp2);
                newe4 = addAreaEdge(G->curScreen, newp2, ro);
                newe5 = addAreaEdge(G->curScreen, newp1, newp2);

                newa1 = addArea(G->curScreen, newe1, newe3);
                newa2 = addArea(G->curScreen, newe2, newe4);
        }

        /*//4 : in loop gaan tot key-up
        while (!loop_done){
                loop_done = 1;
        }
        //5 :                aanpassen van vensterdata
        //6 :                update()*/
        /*printf("areas :\n");
        LIST_printList(G->curScreen->area);
        printf("areaEdges :\n");
        LIST_printList(G->curScreen->areaEdge);
        printf("areaPoints :\n");
        LIST_printList(G->curScreen->areaPoint);
        printf("\n");*/
}

void joinAreas(AreaEdge *ae){
}

AreaEdge *onAreaEdge(int x, int y){
        AreaEdge *a;
        float fx, fy;
        float t, b, l, r;
        float offs = 0.01f;

        fx = (float)x / (float)G->win->x;
        fy = (float)y / (float)G->win->y;

        a = G->curScreen->areaEdge->first;
        while (a){
                t = a->point1->y - offs;
                b = a->point2->y + offs;
                l = a->point1->x - offs;
                r = a->point2->x + offs;

                if (t<=fy && b>=fy && l<=fx && r>=fx) return a;
                a = a->next;
        }

        return 0;
}

---

Now the error occurs when I have a similar situation as described here :

Code:

---

1)
------------------
|                |
|                |
|                |
|                |
|                |
|                |
|                |
------------------
2)
------------------
|        |      |
|        |      |
|        |      |
|        |      |
|        |      |
|        |      |
|        |      |
------------------
3)
------------------
|        |      |
|        |      |
|        |------|
|        |      |
|        |      |
|        |      |
|        |      |
------------------
4)
------------------
|        |      |
|        |      |
|        |------|
|        |      |
|        |------|
|        |      |
|        |      |
------------------

---

This is ofcourse flippable.

The problem happens inbetween situation 3 and 4, when I have called splitAreaWhere(). It crashes at this line :
lb = split->top->point1;
Debugging showed me that split didn't get a value. That is because in the next block, ae->area2 == 0. And this is wrong since ae->area2 shouldn't be NULL.

Code:

---

else{
                where = fy;
                if (fx >= ae->point1->x) split = ae->area2;
                else split = ae->area1;
        }

---

I hope someone has a clue. If this is not clear, or if someone should be interested in this problem, then the complete source can be found here :
http://users.pandora.be/willem.packet1/Gui.zip

Thanks in advance,

Hans

God damn, what a nightmare. Explain in one small paragraph, what you're trying to do. Simply state what you want your program to do, what it does, what it doesn't do that it should, and/or, what it does that it shouldn't.


Quzah.

Quote:

---

I don't known where exactly the error is located

---

A debugger should be able to narrow it down a bit more than that.