Re: [Dev-C++] linked lists...

[Per W. <pw...@ia...>]

By the way - where does the pop function check if there is something to
pop, i.e. that s->firtptr isn't NULL?

/Per W

On Tue, 19 Nov 2002, Oroszi Bal=E1zs wrote:

> Hello j b!
>=20
> Monday, November 18, 2002, 8:16:12 PM, you wrote:
>=20
> jb> i  tried  to  write  a  code  using  linked lists to implement the
> jb> multiplication  and  addition  of twp polynomials but it seems i'm
> jb> not  very  successfull  cause  my pop funcition doesn't do what it
> jb> should  and  i  don't  know  why i get that access violation error
> jb> ..could any one help??
>=20
> > /* definitions*/
> >
> > typedef struct node{
> >   int coefficient;
> >   int exponent;
> >   struct node *next;
> > }node;
> >
> > typedef struct stack{
> >   node *firstptr;
> > }stack;
> >
> > /*and the pop function*/
> >=20
> > node *pop(stack *s){
> >   node *nptr=3Dnew node;
> >   if(nptr=3D=3DNULL){
> >     cout<<"exhausted memory"<<endl;
> >     exit(1);
> >   }
> >   else{
> >     nptr->coefficient=3Ds->firstptr->coefficient;
> >     nptr->exponent=3Ds->firstptr->exponent;
> >     s->firstptr=3Ds->firstptr->next;//that's the problematic part
> >   }
> >   return nptr;
> > }
>=20
> Well  the  above code shouldn't give an access violation error, IF the
> push  (I  assume you have a function named like that) works fine. So I
> think the problem is with the push function.
>=20
> And  one  more  thing. I don't know much about C++, but I'm good at C,
> and  I  think  you should clean up memory when you detatch a node from
> the list.
>=20
> Something like:
>=20
> node *pop(stack *s){
>    node *ntmp; /* Temporary pointer */
>    ...
>    else{
>      ...
>      ntmp =3D s->firstptr;  /*!*/
>      s->firstptr=3Ds->firstptr->next; //that's the problematic part
>      free(ntmp);          /*!*/
>    }
>    return nprt;
> }
>=20
> OR:
> =3D=3D=3D
> Why  not  return only a pointer to the node, instead of creating a new
> one?
> Then the code would be:
>=20
> node *pop(stack *s){
>    node *nptr; /* Only a pointer */
>    nptr =3D s->firstptr;
>    s->firstptr=3Ds->firstptr->next;
>    return nptr;
> }
>=20
> Of  course  you  will  need  to  free  the node that you get, from the
> outside.
>=20
> As  I  stated above, I don't know much about C++, but I've heard, that
> there  are  many  built-in functions, and "things" inside C++ for list
> creation. (They are created through templates, as I remember). Look in
> the book.
>=20
> --=20
> Best regards,
>  Oroszi Bal=E1zs                     mailto:or...@vp...
>=20
> PGP-FP: FB80 8A43 2664 6126 E465  46E2 2546 CFA3 C25B 9F70
> finger -l or...@se... =20
>=20
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