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

[<qa...@ho...>]

Make sure to test that 
s->firstptr !=3D NULL 
otherwise the right-hand-side of the statement 
s->firstptr=3Ds->firstptr->next;
would be 
NULL->next
and that is ofcourse wrong

/J


*********** REPLY SEPARATOR  ***********

On 2002-11-19 at 16:23 Oroszi Bal=E1zs wrote:

>Hello j b!
>
>Monday, November 18, 2002, 8:16:12 PM, you wrote:
>
>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??
>
>> /* definitions*/
>>
>> typedef struct node{
>>   int coefficient;
>>   int exponent;
>>   struct node *next;
>> }node;
>>
>> typedef struct stack{
>>   node *firstptr;
>> }stack;
>>
>> /*and the pop function*/
>> 
>> 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;
>> }
>
>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.
>
>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.
>
>Something like:
>
>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;
>}
>
>OR:
>=3D=3D=3D
>Why  not  return only a pointer to the node, instead of creating a new
>one?
>Then the code would be:
>
>node *pop(stack *s){
>   node *nptr; /* Only a pointer */
>   nptr =3D s->firstptr;
>   s->firstptr=3Ds->firstptr->next;
>   return nptr;
>}
>
>Of  course  you  will  need  to  free  the node that you get, from the
>outside.
>
>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.
>
>-- 
>Best regards,
> Oroszi Bal=E1zs                     mailto:or...@vp...
>
>PGP-FP: FB80 8A43 2664 6126 E465  46E2 2546 CFA3 C25B 9F70
>finger -l or...@se...  
>
>
>
>
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