CODEWITHSUNDEEP
c++
Kai Nyy
Kai Nyy

Reputation: 3

Variable or field declared as void

I have read most posts with the same problem, but I haven't found my problem in those solutions.

I want to wirte a simple linked List with generic content:

But I get the written error "variable or field >>insert<< as void declared" and this for each method except the main.

I hope you can help me, Thanks

#include<iostream>
#include<string>
//EDIT:#include"liste.t" this is waste from a former test
using namespace std;



template <typename T>
struct Element{
    T value;
    Element *next;    

    Element(T v, Element *n) : value(v), next(n)
    { }  
};





template <typename T>
void insert(Element, T, int (*eq)(T,T));
template <typename T>
void remove(Element, T, int (*eq)(T,T));
void print(Element);
template <>
int equal<string>(T, T);
template <typename T>
int equal(T, T);




int main(){    
  int (*eq)(int,int) = equal;
  Element* head=NULL;
  insert(head, 2, eq);
  insert(head, 5, eq);
  insert(head, 1, eq);
  print(head);
  remove(head, 2, eq);
  print(head);
}



template <typename T>
void insert(Element* &rp, T v, int (*eq)(T, T)){
  if(rp!=NULL){
    if(eq(rp->value, v)>=0){ 
      rp = new Element(v, rp);
    }else{
      insert(rp->next, v, eq)
    }
  }else{
    rp = new Element(v, NULL);
  }  
}

 template <typename T>
 void remove(Element * &rp, T v, int (*eq)(T, T)){
   if(rp!=NULL){
     if(eq(rp->value, v)==0){//v 
       Element *tmp = rp;
       rp=rp->next;
       delete tmp;
       remove(rp,v, eq);     
     }else{
       remove(rp->next, v, eq);
     }
   }  
 }

 void print(Element *p){
   while(p){
     cout<<p->value << " ";
     p=p->next;
   }
   cout << endl;
 }


 template <>
 int equal<string>(T a, T b){
   int min=0;
   if(length(a)<length(b)){
     min = length(a);
   }else{
     min=length(b);
   }
   for(int i=0; i< min; i++){
     if(a[i]<b[i])
       return -1;
     if(a[i]>b[i])
       return 1;
   }
   return 0;
 }



 template <typename T>
 int equal(T a, T b){
   if(a<b)
     return -1;  
   if(a>b)
     return 1;
   return 0;  
 }

Upvotes: 0

Views: 1110

Answers (1)

JP Flouret
JP Flouret

Reputation: 618

NOTE: You should probably use std::list or std::forward_list instead of rolling out your own container.

In the function declarations you'll encounter a compile error using Element without a template parameter (this is probably the error you are asking about):

template <typename T>
void insert(Element, T, int (*eq)(T,T));
            ^

This should use Element<T> instead and should also take in a pointer to the Element.

template <typename T>
void insert(Element<T>*, T, int (*eq)(T,T));

The print function also needs to be a template:

template <typename T>
void print(Element<T> *p)

It also appears that you are trying to specialize equals for strings using template specialization. The declaration should read:

template <>
int equal<string>(string, string);

because T is not declared in this context.

I need to stress again that you should really, really consider using std::list or std::forward_list instead of rolling out your own container. There is no need to reinvent the wheel.

Upvotes: 1

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