linked list (Insert)

[momotaro]

why i keep having problem in thhis line:

[CODE=c]
node *InsertVehicule (node *N, vehicule *V)
{
node *pre;
if(!N)
{
N = (node*)malloc(s izeof(node));
N->data_vehicul e = V;
}
else
{
pre = N;
while(pre->NextVehicule )
{
if(pre->data_vehicul e->distance > V->distance)
{
V = pre->NextVehicule->data_vehicul e;
pre->NextVehicule->data_vehicul e = V;
break;
}
else
pre = pre->NextVehicule ;

if(pre->NextVehicule == NULL) // ****THIS ONE****
pre->NextVehicule->data_vehicul e = V;
}
while(N->NextEdge)
printf("%s %d", N->data_vehicul e->CarId, N->data_vehicul e->distance);
}
return N;
}[/CODE]

[weaknessforcats]

pre = pre->NextVehicule ;

if(pre->NextVehicule == NULL) // ****THIS ONE****

You will crash if pre is NULL.

Check pre for NULL before trying to use it in pre->NextVehicule .

[Ganon11]

Additionally, if pre->nextVehicule is NULL (which your if...statement checks), then there will be no pre->nextVehicule->data_vehicul e, so you will crash here as well.

[momotaro]

but i need to reach that status in order to insert at the end!

[momotaro]

I realy don't know how to overcome that NULL pointer issue please help


[CODE=c] node *InsertVehicule (node *N, vehicule *V)
{

node *walker;

if(!N)

{

N = CreatNode();

N->data_vehicul e = V;

printf("%s", N->data_vehicul e->CarId);

}

else

{

walker = N;

while(walker->NextVehicule )

walker = walker->NextVehicule ;

if(!walker->NextVehicule )// ***walker->NextVehicule = NULL***

walker->NextVehicule->data_vehicul e = V;//***hence this line gonna cruch but I need to Insert in here...please help***

}

while(N->NextVehicule )

printf("%s", N->data_vehicul e->CarId);

return N;

}

[/CODE]

[momotaro]

why N is always = NULL

[CODE=c] node *InsertVehicule (node *N, vehicule *V)
{

node *walker;

if(!N)// ***N is always NULL!***

{

N = CreatNode();

N->data_vehicul e = V;

printf("%s", N->data_vehicul e->CarId);

}

else

{

walker = N;

while(walker->NextVehicule )

walker = walker->NextVehicule ;

if(!walker->NextVehicule )

walker->NextVehicule->data_vehicul e = V;

}

while(N->NextVehicule )

printf("%s", N->data_vehicul e->CarId);

return N;

}

[/CODE]

[Laharl]

Create a Vehicle*, then set walker->nextVehicle to it, then change the data values you need. This way, you set the pointer to something, then you can access the pointer safely.

[weaknessforcats]

This code:

walker = walker->NextVehicule ;

if(!walker->NextVehicule )// ***walker->NextVehicule = NULL***

is what I referred to in my Post #2.

walker can be NULL before you get to the if statement. If it is, you will crash. Check you pointers before using the indirection operator (->) on them:
[code=c]
walker = walker->NextVehicule ;
if (!walker)
{
//bail out
return;
}
if(!walker->NextVehicule )// ***walker->NextVehicule = NULL***
[/code]

[momotaro]

but I need that pointer to be null in order to inset a t the end....
am lost plz help

[Laharl]

If the pointer 'walker' points to NULL, then you get a segmentation fault (segfault) when you try to access walker->NextVehicle because NULL has to link to any Vehicle, or anything else for that matter. You can take a NULL pointer and set it to point to something else, but that is the only thing you can do with it (that I know of) other than check if it points to NULL. Anything else gives you segfaults.

As such, you have to check if walker is null before you can do anything with it, since if it is, it'll go kablooie.

[momotaro]

why my linked list is not set!!!! plz help


[CODE=c] node *walker = N;

//printf("%s\n", V->CarId); //all vehicules are ok

if(!N)

{

N = CreatNode();

N->data_vehicul e = V;

}

else

{

while(walker->NextVehicule )

walker = walker->NextVehicule ;

if(!walker->NextVehicule )

{

walker->NextVehicule = CreatNode();

walker->NextVehicule->data_vehicul e = V;

printf("%s\n", N->data_vehicul e->CarId);//there is only the one of thebegining condition****

}

}

return N;

}

[/CODE]

[momotaro]

sill waiting for a help.... :)

[weaknessforcats]

You still haven't made the changes I mentioned in my Post #8.

[momotaro]

to tell you the truth i did not get the meaning of "baikl out"

[Laharl]

"bail out" means to jump out before the ship sinks. In this case, further use in the function will lead to segfaults, so you need to exit before those can happen by using return; which instantly ends a void function (or any other, but anything else needs a value returned).