Why is the code failing in the Destructor? - class

Question

I have gone through stackoverflow questions similar to "Why is the destructor called twice?". My question can be a similar one but with a small change. I am getting an error when running the following code:
struct Employee{
char *name;
char *tag;
Employee *employee;
Employee(){
name = NULL;
tag = NULL;
employee = NULL;
}
//copy constructor
Employee(const Employee &obj){
cout << "Copy constructor called" << endl;
name = (char*)malloc(sizeof(char)*strlen(obj.name));
strcpy(name, obj.name);
tag = (char*)malloc(sizeof(char)*strlen(obj.tag));
strcpy(tag, obj.tag);
employee = (struct Employee*)malloc(sizeof(obj.employee));
employee = obj.employee;
}
//overloaded assignment operator
void operator = (const Employee &obj){
cout << "Assignment operator called" << endl;
if (this == &obj){
return;
}
strcpy(name, obj.name);
strcpy(tag, obj.tag);
employee = obj.employee;
}
//destructor
~Employee(){
cout << "Destructor called" << endl;
if (name != NULL){
cout << "Freeing name" << endl;
free(name);
name = NULL;
}
if (tag != NULL){
cout << "Freeing tag" << endl;
free(tag);
tag = NULL;
}
if (employee != NULL){
cout << "Freeing employee" << endl;
free(employee);
employee = NULL;
}
}
};
Employee createNode(){
Employee emp;
emp.name = (char*)malloc(sizeof(char)* 25);
strcpy(emp.name, "Alan");
emp.tag = (char*)malloc(sizeof(char)* 25);
strcpy(emp.tag, "Engineer");
emp.employee = (struct Employee*)malloc(sizeof(struct Employee));//just created memory, no initialization
return emp;
}
Employee get(){
//Employee emp = createNode();
//return emp;
return createNode();
}
int main(){
Employee emp = get();
getchar();
return 0;
}
I debugged the code and found that error is raising when the destructor is called second time when the main function exits.
1) I want to know why the code fails to run?
2) Are there any memory leaks?
3) How can I fix the error properly deallocating memory?
Thanks in advance.
Update:
As per the three Rule I have also added a copy constructor and overloaded the assignment operator. But the error(Expression : _crtisvalidheappointer(puserdata)) is raising. After checking in the Google I could see that some where the Heap corruption is happening. When I comment the initialization of the Struct member employee in the createNode() then I could see the error raising when trying to free the employee in destructor. So I suspect the problem is with the employee struct member. Please help me with this.I am using Visual studio for debugging and running.

Answer 1

Your problem is a lack of copy construct and assignment operator in your class. As a result you are freeing the strings within the class multiple times.

Answer 2

Just tried your code and found out a few issues that causes a crash:
1) strlen returns length of string without null terminator character, but strcpy requires that additional byte, so your allocating should look like that:
name = (char*)malloc(strlen(obj.name)+1);
2) When you copy employee, you copy pointer, so you have memory leak and employee pointer as a dangling one.
Also malloc cannot work with constructors, therefore after
employee = (struct Employee*)malloc(sizeof(obj.employee));
employee has a garbage inside.