如何在 C++ 中从属于该类的函数访问该类中的向量

Question

I am new in C++. I created a cpp and a header file. Here is the header file:

class LISCH{
public:                 
    class lisch_entry{
    public:
        bool valid;
        int link;
        int data;

        lisch_entry(){
            valid = false;
        }
    };

    vector<lisch_entry> data_vec;


public:

    LISCH(int);
    void insert(int);
    

};

In cpp file , i need to access that data_vec vector in insert function but i couldn't do it because it's my first time coding in C++. Here is the cpp file:

#include "lisch.h"
#include <iostream>

using namespace std;

LISCH::LISCH(int table_size){
   table_size=10;
   int x=5;    
}


void LISCH::insert(int new_data){
   
   
   
   lisch_entry entry;
   int add=new_data%11;
   if(LISCH.data_vec[add] == NULL) //here i need to acces data_vec
   {
       
   }
   data_vec.insert(add,new_data); //and also here

}

How can i manage to do that? I need to check if a specific position of the vector is empty or not.

Answer 1

There are quite a few of things wrong with code, probably for lack of planning or formulating the desired effect.

using namespace std;  // never do this in real programs. 
                      // Even some tests may fail accidently. 

LISCH::LISCH(int table_size){
   table_size=10;  // those are local variables, why assigning values to them?
   int x=5;    
}

data_vec is defined as a vector of lisch_entry :

   vector<lisch_entry> data_vec;

The you out of blue access element of type lisch_entry with index add . Did you allocate that many elements already? It may not exist at all, the program would crash:

   if(LISCH.data_vec[add] == NULL) 

An instance lisch_entry cannot be equal, cannot be compared to NULL as far as you had defined it. The check itself looks suspicious, what had you wanted to do?

  data_vec.insert(add,new_data);

insert receives an iterator as first parameter. An integer value isn't an iterator. It looks like have to check the documentation on std::vector .