Apply operator overriding to classes with dynamic allocation pointers - c++

Question

I have defined the MyString class, and now I want to implement the addition operation. It's horrible for memory leaks to occur, so I've taken care of releasing the dynamically allocated pointers from the destructor.
#include <iostream>
class MyString {
private:
int _size;
char* _str;
public:
MyString() {
_size = 0;
_str = nullptr;
}
MyString(int size, char* str) {
_size = size;
_str = new char[size + 1];
strcpy(_str, str);
}
~MyString() {
delete[] _str;
}
void print() {
std::cout << _str << std::endl;
}
friend MyString operator+(const MyString& lhs, const MyString& rhs);
};
MyString operator+(const MyString& lhs, const MyString& rhs) {
char* temp = new char[lhs._size + rhs._size + 1];
strcpy(temp, lhs._str);
strcat(temp, rhs._str);
MyString ret(lhs._size + rhs._size, temp);
delete[] temp;
return ret;
}
int main() {
MyString first(5, "first");
MyString second(6, "second");
MyString add = first + second;
first.print();
second.print();
add.print();
}
However, if I compile the code and run it, the first.print() and second.print() is printed well, but the add.print() will print the garbage value, and crashes (Debug Assertion Failed!).
Output:
first
second
硼硼硼硼硼硼硼硼?흚 (and creashes :(.. )
If I annotate and run the destructor, it prints well, but a memory leak occurs. Why is this happening? I have looked at several examples of operator overriding, but I have not found an example of this dynamic allocation of pointers.
Any suggestion will be highly appreciated!

Answer 1

MyString operator+(const MyString& lhs, const MyString& rhs) {
char* temp = new char[lhs._size + rhs._size + 1];
strcpy(temp, lhs._str);
strcat(temp, rhs._str);
MyString ret(lhs._size + rhs._size, temp);
delete[] temp;
return ret;
}
At the end of this function 'ret' is destroyed which calls the destructor and deletes the buffer. What is returned is a new instance of MyString that was copied from 'ret', and its buffer points to the same memory location as the original. Since this has been deleted you are now printing out garbage.
To fix this you can add a copy constructor to ensure the buffer is copied:
class MyString {
// Other class details
public:
MyString(const MyString & other) : MyString(other._size, other._str) {}
// Other class details
}
This will ensure the buffer is copied when one MyString is assigned to another MyString.

Answer 2

#include<iostream>
using namespace std;
class Mystring{
private:
int size;
char *str;
public:
friend Mystring operator*(const Mystring &a, const int &d);
friend Mystring operator+(const Mystring &a, const Mystring& b);
friend ostream& operator << (ostream &os, const Mystring a);
friend istream& operator >> (istream &is, const Mystring a);
Mystring (int a, char b) {
this->size = a;
this->str = new char(a);
for (int i = 0; i < a; i++) {
this->str[i] = b;
}
}
~Mystring() {}
};
Mystring operator+(const Mystring &a, const Mystring& b) {
Mystring c(a.size + b.size, { 0 });
for (int i = 0; i < a.size; i++)
{
c.str[i] = a.str[i];
}
for (int i = 0; i < b.size; i++)
{
c.str[a.size + i] = b.str[i];
}
return c;
}
Mystring operator*(const Mystring& a,const int &d){
int z = a.size*d;
Mystring c(z, { 0 });
int k=0;
for (int j = 0; j < d; j++)
{
for (int i = 0; i < a.size; i++)
{
c.str[k+i] = a.str[i];
}
k = a.size + k;
}
return c;
}
ostream& operator << (ostream &os, const Mystring a) {
os << "[";
int i;
for ( i = 0; i < a.size; i++)
{
os << a.str[i];
}
os << "]";
return os;
}
istream& operator >> (istream &is, const Mystring a) {
for (int i = 0; i < a.size; i++)
{
cout << i << "번째 문자 : ";
is >> a.str[i];
}
return is ;
}
int main()
{
int aSize, bSize, iter;
char aInit, bInit;
cout << "문자열A의 크기와 초기문자를 입력: ";
cin >> aSize >> aInit;
Mystring str1(aSize, aInit);
cout << str1 << endl;
cout << "문자열A 입력" << endl;
cin >> str1;
cout << str1 << endl;
cout << "문자열B의 크기와 초기문자를 입력: ";
cin >> bSize >> bInit;
Mystring str2(bSize, bInit);
cout << str2 << endl;
cout << "문자열B 입력" << endl;
cin >> str2;
cout << str2 << endl;
cout << "문자열A와 문자열B 합치기 : ";
Mystring str3 = str1 + str2;
cout << str3 << endl;
cout << "문자열A 반복횟수 입력 : ";
cin >> iter;
Mystring str4 = str1*iter;
cout << str4 << endl;
}
enter code here
why error
~Mystring(){}