Errors in template class

[appleguy]

I am trying to get it to work but I seem to be doing something wrong in the main. Both of my classes are correct.

# include <iostream>
# include <string>
# include <vector>
# include <fstream>
# include <sstream>
# include <cmath> 

using namespace std;

 template < typename T>
 class Deque;

 template < typename T>
class Queue {
   vector <T>* elements;
   int frontSpace;
   int rearItem;
   int maxAdds;
   
   friend class Deque<T>;
   public:
   Queue(int maxAdds) :

   elements ( new vector <T> (maxAdds)),
   frontSpace  (0),
   rearItem (0),
   maxAdds( maxAdds)
   { }
   virtual bool isEmpty() { return frontSpace == rearItem; }
   virtual bool isFull() { return frontSpace == maxAdds; }
   virtual int size() { return frontSpace - rearItem; }
   virtual void pushFront(string newItem) {
      elements->at(frontSpace++) = newItem;
   }
   virtual T popRear() {
      if (isEmpty()) {
       cerr <<"Later we'll define and throw an EmptyQException" << endl;
       return "";
      }
        else
       {
         return elements -> at (rearItem++);
       }
   }
   virtual T toString()
     {
      T out("");
      for (int i = rearItem; i < frontSpace; i++)
     {
         out += elements ->at(i) + " ";
      }
      return out;
   }
};	
  template <class T>
  class Deque: public Queue<T>  {     
          friend class Queue<T>;	

  public: Deque<T> (int maxAdds) : Queue<T> (2*maxAdds)  
          {this->frontSpace = maxAdds;    
           this->rearItem = maxAdds ;			
          }  



          virtual void pushRear(T newItem) {
          if (this -> isFull()){
             cerr << "later we'll define and throw a FullDQException" << endl;
             cerr << this->toString() << endl;
          } else {					
            this-> elements->at(--(this->rearItem)) = newItem;
          }
        }   

          virtual T popFront() {	
          if (Queue<T>::isEmpty()) {
          cerr <<"Later we'll define and throw an EmptyQException" << endl;
          return "";
          }
           else {
          return this->elements -> at (--this->frontSpace);
          }
          } 

          virtual bool isFull() const {
          return(Queue<T>::isFull() || this -> rearItem ==0);
         
      }    
        
    
		

    }; 
  bool ed1(const string& x, const string& y){
     int xlen = x.length();
     int ylen = y.length();
     if (abs(xlen - ylen) >= 2) {return false;}	
     if (xlen == ylen) {
        int count = 0;
        for (int i = 0; i < xlen; i ++) {
           if (x.at(i) != y.at(i)) {count++;}
        }  
        return (count == 1);
     }
     else if (xlen == ylen +1) {
        for (int i= 0; i < ylen; i++) {
           if (x.at(i) != y.at(i)) {
              return (x.substr(i+1)== (y.substr(i)));
           } 
        } 
        return true;
     }

     else if (ylen == xlen +1) {
        for ( int i = 0; i< xlen; i++){
           if (y.at(i) != x.at(i)) {
              return( y.substr(i+1)==(x.substr(i)));  
           } 
        }  
        return true;
    }
}  
  
int main () {

   Queue* sq = new Queue(100);
   sq->pushFront("oh");
   sq->pushFront("say");
   sq->pushFront("can");
   sq->pushFront("you");
   sq->pushFront("see");
   cout << (sq->toString())<< endl;
   T pop2 = sq->popRear() + " " + sq->popRear();
   cout << (pop2 + ", did this print in the right order?")<< endl;
   sq->pushFront("me?");
   cout <<("Final queue: " + sq->toString())<< endl;

  Deque* sd = new Deque(100); 
   T infileName = "words.txt";    
   ifstream* INFILEp = new ifstream(infileName.c_str(), ios_base::in);
   T word;
   while((*INFILEp) >> word)    {
     if (sd->isEmpty()) {
        sd-> pushFront(word);
     }  
     else {
        frontWord = sd->popFront();
        sd->pushFront(frontWord);
        rearWord = sd->popRear();
        sd->pushRear(rearWord);
        if(ed1(word , frontWord)) {
cerr << "Pushing " << word << " on front " << endl;
           sd->pushFront(word);
        }
        else if(ed1(word , rearWord)) {
cerr << "Pushing " << word << " to rear " << endl;
           sd-> pushRear(word);
        }
        else if(ed1(word, rearWord) && ed1( word , frontWord)) {
           sd->pushFront(word);
        } 
        else {
        }  //don nothing, just skip word
     }

  }
  cout << "Final contents: " << sd->toString() << endl;
   
  return 0;
}

I keep getting these errors:

In function ‘int main()’:
141: error: missing template arguments before ‘*’ token
141: error: ‘sq’ was not declared in this scope
141: error: expected type-specifier before ‘Queue’
141: error: expected `;' before ‘Queue’
148: error: ‘T’ was not declared in this scope
148: error: expected `;' before ‘pop2’
149: error: ‘pop2’ was not declared in this scope
153: error: missing template arguments before ‘*’ token
153: error: ‘sd’ was not declared in this scope
153: error: expected type-specifier before ‘Deque’
153: error: expected `;' before ‘Deque’
154: error: expected `;' before ‘infileName’
155: error: ‘infileName’ was not declared in this scope
156: error: expected `;' before ‘word’
157: error: ‘word’ was not declared in this scope
162: error: ‘frontWord’ was not declared in this scope
164: error: ‘rearWord’ was not declared in this scope

[hamsterman]

Whenever you use a template you have to specify the template parameters. The right way would be Queue<string>* sq = new Queue<string>(100);. The same for Deque.
In some cases, template parameters can be deduced. This is not one of those cases, however.
When you write template<typename T> the T is only a valid identifier inside the class/function. In main this T is not known. Write string.

[appleguy]

Is there a way for me to use the T inside the int main?

[filipe]

T is not a type, it's just a placeholder for a type. You need to specify what type you're talking about, as hamsterman said.

[hamsterman]

You could create another template function..

template<typename T>
void this_is_totally_not_main(){
   Queue<T>* sq = new Queue<T>(100);
   //...
   T word;
   //...
}

int main(){
   this_is_totally_not_main<string>();
   return 0;
}