Compiler Error: ‘std::array<...>::~array()’ is implicitly deleted

Question

I have the following .hpp file:

#ifndef CODE_HPP
#define CODE_HPP
#include <array>
#include <vector>
using std::vector;
using std::array;

template<typename T, typename C = vector<T>>
class stack;

template<typename T, typename C = vector<T>, typename K = stack<T,C>>
class stack_array;

template<typename T, typename C>
class stack
{
    C pile;

    stack();
    ~stack();
    void push(T&);
    friend class stack_array<T,C,stack<T,C>>;
};


template<typename T, typename C, typename K>
class stack_array
{
    private:
        static const size_t max_elem = 10;
        array<K, max_elem> store{};
        size_t index;
    public:
        stack_array(T&);
        ~stack_array();
};


template<typename T, typename C> stack<T,C>::stack(){
    pile.clear();
}

template<typename T, typename C> stack<T,C>::~stack(){
}

template<typename T, typename C> void stack<T,C>::push(T& _data){
    pile.push_back(_data);

    return;
}

template<typename T, typename C, typename K> stack_array<T,C,K>::stack_array(T& _data){

    index = 0;

    store[index].push(_data);
}

template<typename T, typename C, typename K> stack_array<T,C,K>::~stack_array(){
}

#endif

My .cpp file is reproduced below:

#include "code.hpp"
#include <iostream>
using std::cout;

int main (void){

    auto i = 0;
    stack_array<decltype(i)> s_a(i);

    return 0;
}

When the above code is compiled using the following command:

g++ -ggdb -std=c++17 -Wall main.cpp code.hpp

I get the following compilation error:

In file included from main.cpp:1:0:
code.hpp: In instantiation of ‘stack_array<T, C, K>::stack_array(T&) [with T = int; C = std::vector<int, std::allocator<int> >; K = stack<int, std::vector<int, std::allocator<int> > >]’:
main.cpp:8:35:   required from here
code.hpp:52:86: error: use of deleted function ‘std::array<stack<int, std::vector<int, std::allocator<int> > >, 10>::~array()’
 template<typename T, typename C, typename K> stack_array<T,C,K>::stack_array(T& _data){
                                                                                      ^
In file included from code.hpp:3:0,
                 from main.cpp:1:
/usr/lib/gcc/x86_64-pc-cygwin/7.4.0/include/c++/array:94:12: note: ‘std::array<stack<int, std::vector<int, std::allocator<int> > >, 10>::~array()’ is implicitly deleted because the default definition would be ill-formed:
     struct array
            ^~~~~

Why is the destructor for std::array getting invoked because of the code inside stack_array<T,C,K>::stack_array()?

that is intentional...the stack ctor() is getting invoked from within the friend class stack_array — Vinod
– Vinod, Commented Jul 23, 2019 at 7:53
how do you expect the array destructor to work if it can't access the destructor of the items in it ? More details : en.cppreference.com/w/cpp/language/… — Sander De Dycker
– Sander De Dycker, Commented Jul 23, 2019 at 7:59
presume that observation is correct,,,I got rid of the destructor for the stack class which wasn't doing much anyway, and the error disappeared... — Vinod
– Vinod, Commented Jul 23, 2019 at 8:06
if you didn't explicitly delete the destructor, there will be an implicitly defined (public) destructor in that case (which makes std::array happy). If you explicitly delete the destructor, you should get the same error. — Sander De Dycker
– Sander De Dycker, Commented Jul 23, 2019 at 8:10
I didn't explicitly delete the destructor using =delete; rather just let the compiler define a default destructor for stack by removing the declaration and definition altogether. And that got rid of the error. — Vinod
– Vinod, Commented Jul 23, 2019 at 8:13

Martin Morterol · Accepted Answer · 2019-07-23 08:02:02Z

4

You should add std::array as friend

template<typename T, typename C>
class stack
{
    C pile;

    stack();
    ~stack();
    void push(T&);
    friend class stack_array<T,C,stack<T,C>>;

    template< class TT, std::size_t N>  friend class std::array ;
};

demo : https://wandbox.org/permlink/TxAyRCvrwj9CtOhV

The message say : std::array<stack<int, std::vector<int, std::allocator<int> > >, 10>::~array()’ is implicitly deleted...

So you have an std::array of stack<smt>, std::array should be able to delete stack or its destructor is private => the destructor of array is implicitly deleted.

So you have to make it accessible to std::array by making it public or friend.

answered Jul 23, 2019 at 8:02

Martin Morterol

3,0121 gold badge14 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Compiler Error: ‘std::array<...>::~array()’ is implicitly deleted

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related