Template Membership Problems?

Question

I get errors for the below code when I try to compile that tell me the following:

'isEmpty' : is not a member of '_Stack'

Error while compiling class template member function 'void QueueS::enqueue(const T &)

#include <iostream>
#include <stack>
using namespace std;

template <class T>
class _Stack : public stack<T> {

public:

   T pop(){
       T tmp=stack::top();
       stack::pop();
       return tmp;
   }
};

template <class T>
class QueueS {
public:
    QueueS(){}

   bool isEmpty() const{

   }


   void enqueue(const T& el){

    while (!output.isEmpty()) {
         input.push(ouput.pop());
    }

    input.push(el);

    }

 private:

 _Stack<T> input;
 _Stack<T> output;

};

I'm not sure what's going on. Can anyone offer any assistance? I have obviously not implemented isEmpty yet. Was wondering if that should have an effect.

One problem is that `'isEmpty' : is not a member of '_Stack'`. This is nothing to do with templates. — juanchopanza, Jun 08 '13 at 23:54
What do you think `stack::top()` returns? `top` is a member function and it should be called off an *instance* of `std::stack`. — David G, Jun 08 '13 at 23:54
Unrelated to your problem, but still: You shouldn't use identifiers that start with underscore and uppercase letter (such as `_Stack`). See [here](http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier) for a related SO post. — jogojapan, Jun 09 '13 at 00:08
Better indentation would help to see that `isEmpty` is clearly defined outside the `_Stack` template. — jogojapan, Jun 09 '13 at 00:10
Sorry; the indentation is clearer in my own code, but I always run into difficulty trying to paste something in the given code brackets here. — Rome_Leader, Jun 09 '13 at 00:18
Would have tried to help if only this code was more readable, it's impossible to know what is going on... — Ravid Goldenberg, Jun 09 '13 at 00:20
Indentation should be better now. I see the point now about the isEmpty() usage. I should probably be using the library defined .empty instead. Still I'm confused about the latter error. — Rome_Leader, Jun 09 '13 at 00:29

Ravid Goldenberg · Answer 1 · 2013-06-09T17:46:03.340

1

What is it you are trying to do? That wont work since isEnpty is a member function of the class _stack. You can solve the first problem by adding the function isEmpty to your _Stack class.

Like so:

#include <iostream>
#include <stack>
using namespace std;

template <class T>
class _Stack : public stack<T> 
{

public:

T pop(){
T tmp=stack::top();
stack::pop();
return tmp;
}
bool isEmpty() const{

return stack::empty();
}
};

template <class T>
class QueueS {


public:
QueueS(){}

bool isEmpty() const{

}


void enqueue(const T& el){

while( !output.isEmpty()) {
input.push(output.pop());
}

input.push(el);

}

 private:
 _Stack<T> input;
 _Stack<T> output;

};


int main()
 {
 _Stack<int> sk;
 sk.isEmpty();
 QueueS<int> qu;
 qu.enqueue(4);
 return 1;
 }

edited Jun 09 '13 at 17:46

answered Jun 09 '13 at 00:30

Ravid Goldenberg

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I was just trying to use it as a check. Since my stacks are private, I was going to attempt to use the function (once written) as a go between for accessing them. Since they're declared in separate classes, though, might I be better off just using the library's .empty() check? – Rome_Leader Jun 09 '13 at 00:33
I'd still need an instance of the object to make that change, wouldn't I? I "get use of class template requires template argument list", and I believe that's what it is saying. – Rome_Leader Jun 09 '13 at 12:31
I am not quite sure what do you mean, maybe if you will add your main or the line that gave you the error. – Ravid Goldenberg Jun 09 '13 at 15:54
The line return std::empty() gives the error use of class template requires template argument list. – Rome_Leader Jun 09 '13 at 17:27
I still don't know what do you mean, I re edited the post with a main and this worked fine where is the problem? – Ravid Goldenberg Jun 09 '13 at 17:42
Verified your solution! My compiler was stuck on some garbage I had introduced in a previous solution. All good, thanks! – Rome_Leader Jun 09 '13 at 22:08

Template Membership Problems?

1 Answers1