So what I am trying to do, I have two classes named ClassA and ClassB, in ClassB there exists a pointer which is referring to an array of ClassA objects. But when I am trying to save the objects inside the array the details are not getting reflected. I tried debugging the same and it's giving me segmentation fault. Is there anything I am doing wrong?

Classes File:

#include <bits/stdc  .h>
using namespace std;

class ClassA{
    private:
        string name;
        string phone;
    public:
        ClassA(string name, string phone)
        {
            this->name = name;
            this->phone = phone;
        }
        string getName()
        {
            return name;
        }
        string getPhone()
        {
            return phone;
        }
};

class ClassB{
    private:
        ClassA* details;
        int size;
    public:
        ClassB()
        {
            size = 0;
            details = (ClassA*)malloc(5*sizeof(ClassA));
        }
        void addDetails(string name, string phone)
        {
            ClassA* temp = new ClassA(name, phone);
            details[size  ] = *temp;
            // cout<<details[size-1].getName()<<" "<<details[size-1].getPhone()<<endl;
        }
        void print()
        {
            for(int i = 0; i < size; i  )
            {
                cout << details[i].getName() << " " << details[i].getPhone() << endl;
            }
        }
};

Driver Code:

#include "temp.h"
using namespace std;

int main()
{
    ClassB b;
    b.addDetails("A", "123");
    b.addDetails("B", "456");
    b.addDetails("C", "789");
    b.print();
    return 0;
}

Anyone, please help me out on this.

CodePudding user response：

When you are calling malloc you won't call the constructor, so ClassA is not constructed. Plus, your malloc put only allocate a place for one object. You better use std::vector, see the example below.

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

class ClassA{
private:
    string name;
    string phone;
public:
    ClassA(string name, string phone)
    {
        this->name = name;
        this->phone = phone;
    }
    string getName()
    {
        return name;
    }
    string getPhone()
    {
        return phone;
    }
};
class ClassB{
private:
    std::vector<ClassA> details;

public:
   
    void addDetails(string name, string phone)
    {
        details.emplace_back(name, phone);
        //cout<<details[details.size()-1].getName()<<" "<<details[details.size()-1].getPhone()<<endl;
    }
    void print()
    {
        for(int i = 0; i < details.size(); i  )
        {
            cout << details[i].getName() << " " << details[i].getPhone() << endl;
        }
    }
};

int main()
{
    ClassB b;
    b.addDetails("A", "123");
    b.addDetails("B", "456");
    b.addDetails("C", "789");
    b.print();
    return 0;
}   

CodePudding user response：

You are mixing malloc and new, which causes undefined behavior.

The C library function malloc() does not initialize the memory nor call the initializer of the class, since C does not have classes. That's why you should never call malloc() to allocate heap memory for classes/structs in C . Whereas new is a operator which returns the exact data type and calls the initializer of the class\struct.

Some Problems:

• Use size_t to store length of the array.
• Use std::vector to store unknown amount of similar data type.
• If parameter is not going to change inside the function, write it as const std::string &
• do not include <bits/stdc .h>
• do not write this using namespace std;

So, you final code should be TRY IT ONLINE:

#include <iostream>
#include <vector>

class ClassA{
    private:
        std::string name;
        std::string phone;
    public:
        ClassA(const std::string &name, const std::string &phone)
        {
            this->name = name;
            this->phone = phone;
        }
        std::string getName()
        {
            return this->name;
        }
        std::string getPhone()
        {
            return this->phone;
        }
};

class ClassB{
    private:
    std::vector<ClassA> vec;
    public:
        ClassB() = default;
        void addDetails(const std::string &name, const std::string &phone)
        {
            vec.push_back(ClassA(name, phone));
        }
        void print()
        {
            for (auto &&i : vec){
                std::cout << i.getName() << " " << i.getPhone() << "\n";
            }
            std::cout << std::endl;
        }
};

int main(void)
{
    ClassB b;
    b.addDetails("A", "123");
    b.addDetails("B", "456");
    b.addDetails("C", "789");
    b.print();
    return 0;
}