deep copying using copy constructor c++

Question

I am trying to implement my own CString class. I am facing some problem in shallow copying the pointer. Here is the class

#include<iostream>
#include<string.h>
using namespace std;

class myCString{
public:
    myCString(){
        m_value = NULL;
    }
    myCString(char* strParam){
        int len = length(strParam);
        m_value = new char[len+1];
        for(int i=0;i<len; i++)
        {
            m_value[i] = strParam[i];
        }
        m_value[len]='\0';

    }
    myCString(const myCString& obj)
    {
        int len = obj.length();
        m_value = new char[len+1];
        for(int i=0;i<len; i++)
        {
            m_value[i] = obj.m_value[i];
        }
        m_value[len]='\0';
    }
        myCString(const myCString *obj)
    {
        int len = obj->length();
        m_value = new char[len+1];
        for(int i=0;i<len; i++)
        {
            m_value[i] = obj->m_value[i];
        }
        m_value[len]='\0';
    }
     const int length() const
    {
        return length(m_value);
    }
    myCString operator=(myCString obj)
    {
        int i=0;
        int length= obj.length();
        m_value = new char[length + 1];
        for(;i<obj.length(); i++)
        {
            m_value[i] = obj.m_value[i];
        }
        m_value[length]='\0';
        return m_value;
    }

    ~myCString()
    {
        delete []m_value;
        m_value = NULL;
    }
    friend ostream& operator<<(ostream& os, const myCString obj);
private:
    const int length(char* strParam)const
    {
        int i=0;
        while(strParam[i]!='\0'){
        i++;
        }
        return i;
    }
    char *m_value;
};
ostream& operator<<(ostream& os, myCString obj)
    {
        os<<obj.m_value;
        return os;
    }

and here is the main():

#include"myCString.h"
int main()
{
    myCString *ptr = new myCString("Hi! This is myCString\n");
    cout<<*ptr;
    myCString *ptr2 = ptr;
    delete ptr;
    cout<<*ptr2;
    delete ptr2;
    return 0;
}

The issue is when shallow copy happens; i know that writing

myCString *ptr2 = new myCString(ptr); 

will fix the issue; but i want to keep the main function intact and make some changes in the class. Is there anyway i can do it? Thanks in advance.

Answer 1

将您的myCString(char* strParam)签名更改为

myCString(const char* strParam)

Answer 2

Your request is to make a deep copy of the objekt in the line myCString *ptr2 = ptr , but this aim is not reachable by object's class programing, because this line only copies a pointer and does not involve the object's class. If you like to call the copy constructor, You must write as You suggested: myCString *ptr2 = new myCString(ptr) ; or You can write:

myCString mystr("Hi! This is myCString\n");
cout<<mystr;
myCString mystr2 =mystr;
cout<<mystr;

Another problem: calling function ostream& operator<<(ostream& os, myCString obj) the copy operator myCString(const myCString& obj) is called for parameter obj. You should write

ostream& operator<<(ostream& os, const myCString& obj)

to avoid this.