Why can't my loop detect \0 symbol in const string? - c++

Question

#include<iostream>
#include<string>
#include<sstream>
#include <typeinfo>
#include<cmath>
#include<vector>
#include <algorithm>
using namespace std;
class Mystring {
char *arr;
public:
Mystring(const char pointer[]) {
int i = 0;
while (pointer[i] != '\0') {
i++;
cout << pointer[i] << endl;
}
arr = new char[i];
i = 0;
while (pointer[i] != '\0') {
arr[i] = pointer[i];
i++;
}
}
friend ostream& operator<<(ostream& out, Mystring& str) {
int i = 0;
while (str.arr[i] != '\0') {
out << str.arr[i];
i++;
}
return out;
}
};
int main() {
Mystring string("Hello, world!");
cout << string << endl;
}
I'm trying to create my own string class. The length of "hello world!" is 13, but the length of arr turns out to be 17. It is filled with some strange chars for some reason I don't understand. When I'm trying to cout string it returns this: Hello, world!¤¤¤¤.

Answer 1

You forgot to add '\0' at the end of your arr[].
Moreover, the size or arrshould be increased to incorporate this \0, as noted in #user7860670's answer.
Moreover, using string as a variable name, in addition to using namespace std;, is confusing at least.
#include<iostream>
#include<string>
#include<sstream>
#include <typeinfo>
#include<cmath>
#include<vector>
#include <algorithm>
//using namespace std;
class Mystring {
char *arr;
public:
Mystring(const char pointer[]) {
int i = 0;
while (pointer[i] != '\0') {
i++;
std::cout << pointer[i] << std::endl;
}
arr = new char[i+1];
i = 0;
while (pointer[i] != '\0') {
arr[i] = pointer[i];
i++;
}
arr[i] = '\0';
}
friend std::ostream& operator<<(std::ostream& out, const Mystring& str) {
int i = 0;
while (str.arr[i] != '\0') {
out << str.arr[i];
i++;
}
return out;
}
};
int main() {
Mystring mstring("Hello, world!");
std::cout << mstring << std::endl;
}

Answer 2

Buffer size required to hold "Hello, world!" (including terminating null) is 14 while you only allocate space for 13 chars and completely omit terminating null. So during iteration inside of operator<< buffer index will go out of bounds which is Undefined Behavior.
You should allocate one extra byte and make sure that buffer ends with terminating null
arr = new char[i + 1];
i = 0;
while (pointer[i] != '\0')
{
arr[i] = pointer[i];
++i;
}
arr[i] = '\0';