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POHow to properly use protected in singly linked list
 

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  1. POHow to properly use protected in singly linked list
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    <p>I've successfully programmed a singly linked list by the following program: The header file is:</p> <pre><code>#ifndef SLL_H_ #define SLL_H_ #include &lt;iostream&gt; class node { protected: public: int key; node *next; node(); ~node(); }; class SLL : public node{ private: node *Head = NULL; int SLL_SIZE = 0; public: //Constructor SLL(); //SLL(int n); //Destructor ~SLL(); //Modifiers void Push_Front(int a); void Push_Back(SLL A,int b); void Traverse(); //Access function int SLL_size(); int Get(node* p); //Iterator node* Begin(); node* End(); //void Search(int a); }; #endif </code></pre> <p>SLL.cpp</p> <pre><code>#include "SLL.h" #include &lt;iostream&gt; using namespace std; node::node(){ cout &lt;&lt; "Empty constructor of node is being called;" &lt;&lt; endl; } node::~node(){ cout &lt;&lt; "Empty destructor of node is being called;" &lt;&lt; endl; } SLL::SLL():node(){ cout &lt;&lt; "Empty constructor of SLL is being called;" &lt;&lt; endl; } SLL::~SLL(){ cout &lt;&lt; "Empty destructor of SLL is being called." &lt;&lt; endl; } //Insert element at the front of the list void SLL::Push_Front(int k){ node *temp = new node [1]; temp-&gt;key = k; temp-&gt;next = Head; Head = temp; SLL_SIZE = SLL_SIZE + 1; } //Insert element at the end of the list void SLL::Push_Back(SLL A, int m){ node *temp1 = A.End(); node *temp2 = new node [1]; temp2-&gt;key = m; temp1-&gt;next = temp2; temp2-&gt;next = NULL; SLL_SIZE = SLL_SIZE + 1; } //Insert element at a given position //Return the number of elements in the linked list int SLL::SLL_size(){ return SLL_SIZE; } //Traverse the list (print the list) void SLL::Traverse(){ node *temp; temp = Head; while(temp!=NULL){ cout &lt;&lt; temp-&gt;key &lt;&lt; " "; temp = temp-&gt;next; } cout &lt;&lt; endl; } //Get key given pionter int SLL::Get(node* pt){ if(pt!=NULL){ node* temp = pt; return temp-&gt;key; } else { cout &lt;&lt; "Null pointer points to nowhere!" &lt;&lt; endl; return 0; } } //Return the pointer at the beginning of the list node* SLL::Begin(){ return Head; } //Return the pointer at the end of the list node* SLL::End(){ node* temp = Head; while(temp-&gt;next!=NULL){ temp = temp-&gt;next; } return temp; } </code></pre> <p>main.cpp</p> <pre><code>#include &lt;iostream&gt; #include "SLL.h" using namespace std; int main() { SLL A; A.Push_Front(1); A.Push_Front(2); A.Push_Front(5); A.Push_Front(6); A.Push_Back(A,3); A.Traverse(); cout &lt;&lt; A.SLL_size() &lt;&lt; endl; cout &lt;&lt; A.Get(A.Begin()) &lt;&lt; endl; cout &lt;&lt; A.Get(A.End()) &lt;&lt; endl; return 0; } </code></pre> <p>One error is, for example :</p> <pre><code>SLL.h||In member function 'void SLL::Push_Front(int)':| SLL.h|7|error: 'int node::key' is protected| SLL.cpp|25|error: within this context| SLL.h|8|error: 'node* node::next' is protected| SLL.cpp|26|error: within this context| SLL.h||In member function 'void SLL::Push_Back(SLL, int)':| SLL.h|7|error: 'int node::key' is protected| SLL.cpp|35|error: within this context| SLL.h|8|error: 'node* node::next' is protected| LL.cpp|36|error: within this context| SLL.h|8|error: 'node* node::next' is protected| SLL.cpp|37|error: within this context| </code></pre> <p>Similar error for the other member functions that employed key and next.</p> <p>This program works very well now. However, after I moved the 2 lines in <code>node</code> class, <code>int key; node *next;</code> under <code>protected</code>, then it gives me error such as "node::key is protected".</p> <p>First, please don't blame me for doing something stupid :P . I know if I <code>struct</code> for the node then life will be much easier. I am trying to practice inheritance and to understand protected. That's why.</p> <p>By definition, protected members can be accessed by derived class, right? I don't know where I am doing it wrong.</p> <p>Hope you can help me out. Thanks! </p>
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    1. COHow about showing the line that error is occurring at and the actual compile error you are getting?
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    2. COIt appears you're trying to set `key` and `next` from outside the class, rather than methods in the class.
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    3. CO@greatwolf, yea, the exact error shown in the compiler is "SLL.h|7|error: 'int node::key' is protected"
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