I don't know what's happening but added 3 constructors, destructors and also a move assignment operator and then created 3 objects with various tasks to test it out but just getting output as "parameterized constructor called" meaning only first object gets called. help!!I have added some code and modified several parts of it, but the post cannot be submitted. It is fine if this message appears when asking a new question, but it appears when I am trying to resubmit my edited post.

How can I solve this?

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

class mystring{ //class definition
    char *str;
    public:

    void display(){
        cout<<str<<endl;
    }

    mystring():str(nullptr){        //Default constructor
           cout<<"default constructor called"<<endl;
           str=new char[1];
           *str='\0';
    }

    mystring(const char *s):str(nullptr){       //Parameterized constructor
        cout<<"parameterized constructor called"<<endl;
        if(s==nullptr)
            str=new char[1];
            *str='\0';
        str= new char[strlen(s) 1];
        strcpy(str,s);
    
    }

    mystring(const mystring &rhs):str(nullptr){     //Copy constructor

        cout<<"Copy constructor called"<<endl;
        if(rhs.str==nullptr)
            this->str=new char[1];
            this->str[0]='\0';
        str=new char[strlen(rhs.str) 1];
        strcpy(str,rhs.str);


    } 

    ~mystring(){                   //destructor
        cout<<"Destructor called"<<endl;
        delete[] str;   
    }

    mystring &operator=(const mystring &rhs){       //Copy assignment

        cout<<"Copy assignment"<<endl;
        if(this==&rhs)
            return *this;
        delete[] str;
        str=new char[strlen(rhs.str)];
        strcpy(str,rhs.str);
        return *this;
    }





};






int main(){
    mystring a("Damn");
    mystring b=a;
    a="hot damn";
    mystring c(a);
    a.display();
    b.display();
    c.display(); 
    return 0;
}

CodePudding user response：

Why is my Move assignment operator not working?

There is no move assignment operator in the presented by you code. There is only the copy assignment operator that has a bug

mystring &operator=(const mystring &rhs){       //Copy assignment

    cout<<"Copy assignment"<<endl;
    if(this==&rhs)
        return *this;
    delete[] str;
    str=new char[strlen(rhs.str)];
    strcpy(str,rhs.str);
    return *this;
}

You have to write

str=new char[strlen(rhs.str)   1];

instead of

str=new char[strlen(rhs.str)];

Also there are another bugs. For example in this constructor

mystring(const char *s):str(nullptr){       //Parameterized constructor
    cout<<"parameterized constructor called"<<endl;
    if(s==nullptr)
        str=new char[1];
        *str='\0';
    str= new char[strlen(s) 1];
    strcpy(str,s);

}

there is a memory leak. The memory allocated twice

str=new char[1];
str= new char[strlen(s) 1];

You should write

mystring(const char *s):str(nullptr){       //Parameterized constructor
    cout<<"parameterized constructor called"<<endl;
    if ( s == nullptr )
    {
        str=new char[1];
        *str='\0';
    }
    else
    {
        str= new char[strlen(s) 1];
        strcpy(str,s);
    }
}

The same problem exists in the copy constructor. You have to write

mystring(const mystring &rhs):str(nullptr){     //Copy constructor
    cout<<"Copy constructor called"<<endl;

    str=new char[strlen(rhs.str) 1];
    strcpy(str,rhs.str);
}

If you will make the changes then the program output will be

parameterized constructor called
Copy constructor called
parameterized constructor called
Copy assignment
Destructor called
Copy constructor called
hot damn
Damn
hot damn
Destructor called
Destructor called
Destructor called

CodePudding user response：

//Try to call mystring::mystring(const char*):


//                    pass a null pointer to the object data pointer
//                          V
mystring(const char *s):str(nullptr)
{

    cout<<"parameterized constructor called"<<endl;
    //if const char* == null,
    //then allocate memory for object data
    if(s==nullptr)
    //This line will not be executed if you pass a string literal. Because a string literal does not point to null
        str=new char[1];
    //If the previous line failed, then you cannot access the data (points to null)
    *str='\0';
    str= new char[strlen(s) 1];
    strcpy(str,s);

}

in main function:

//class Object  Constructor paremeter: const char*
// V     V      V
mystring a("Damn");