问题
I am studying CPP templates myself and got stuck while trying templates of templates parameters for a class. I am getting errors when I am trying to instantiate the class member.
#pragma once
#include "stdafx.h"
# include <list>
template<class type, template<type> class T>
class stack
{
private:
int count;
int size;
T<type> st;
public:
stack(size_t size):size(100), count(-1){ }
void push(type elem);
type pop();
};
template<class type, template<type> class T>
void stack<type, T>::push(type elem)
{
if (count < (size - 1))
{
st.push_back(elem);
count++;
}
else
{
cout << "Elements cannot be added to the internal stack" << endl;
}
}
template<class type, template<type> class T>
type stack<type, T>::pop()
{
if (count < 0)
{
cout << "Stack is empty," << endl;
}
else
{
T elem = st.back();
st.pop_back();
count--;
return elem;
}
}
void test_stack_class()
{
stack<int, list> s1(10);
/*s1.push(vec);
s1.push(22);
s1.push(40);
s1.push(12);
s1.push(7);
cout << "Stacks pops: " << s1.pop() << endl;
cout << "Stacks pops: " << s1.pop() << endl;
*/
}
Kindly help me get over this error and try to explain a bit. I think somehwere my understanding about templates is weak that even after referring many online sites I am not able to get to the issue.
Update:- I am getting these errors.
Severity Code Description Project File Line Suppression State
Error C2514 'stack': class has no constructors templates_learning c:\users\bhpant\source\repos\templates_learning\templates_learning\stack.h 58
Error C2993 'type': illegal type for non-type template parameter '__formal' templates_learning c:\users\bhpant\source\repos\templates_learning\templates_learning\stack.h 12
Error (active) E0999 class template "std::list" is not compatible with template template parameter "T" templates_learning c:\Users\bhpant\source\repos\templates_learning\templates_learning\stack.h 58
Error C3201 the template parameter list for class template 'std::list' does not match the template parameter list for template parameter 'T' templates_learning c:\users\bhpant\source\repos\templates_learning\templates_learning\stack.h 58
回答1:
You're declaring template template parameter incorrectly. Change
template<class type, template<type> class T>
class stack
to
template<class type, template<typename> class T>
class stack
BTW: std::list has two template parameters (the 2nd one has default value), but T has only one; they don't match. Since C++17 it works fine but if your compiler doesn't support C++17 well you might have to use parameter pack to solve the issue.
template<class type, template<typename...> class T>
class stack
来源：https://stackoverflow.com/questions/50656291/errors-while-using-templates-templates-parameters