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Preventing Object Copy in C++
In C++, when classes are created, we can copy it using some copy constructor or assignment operator. In this section we will see, how to prevent object copy of a class in C++. To prevent object copy, we can follow some rules. These are like below.
1. Creating private copy constructor and private assignment operator.
Example
#include <iostream>
using namespace std;
class MyClass {
int x;
public:
MyClass() {
//non-parameterized constructor
}
MyClass(int y): x(y) {
}
private:
MyClass(const MyClass& obj) : x(obj.x) {
//private copy constructor
}
MyClass& operator=(const MyClass& tmp_obj) {
//private assignment operator (overloaded)
x = tmp_obj.x;
return *this;
}
};
main() {
MyClass ob(50);
MyClass ob2(ob); // calls copy constructor
ob2 = ob; // calls copy assignment operator
}Output
[Error] 'MyClass::MyClass(const MyClass&)' is private [Error] within this context [Error] 'MyClass& MyClass::operator=(const MyClass&)' is private [Error] within this context
2. Inherit dummy class with private copy constructor, and private assignment operator.
Example
#include <iostream>
using namespace std;
class DummyClass {
public:
DummyClass() {
}
private:
DummyClass(const DummyClass& temp_obj) {
}
DummyClass& operator=(const DummyClass& temp_obj) {
}
};
class MyClass : public DummyClass {
int x;
public:
MyClass() { }
MyClass(int y) : x(y) {
}
};
int main() {
MyClass ob1(50);
MyClass ob2(ob1); // Calls copy constructor
ob2 = ob1; // Calls copy assignment operator
}Output
[Error] 'DummyClass::DummyClass(const DummyClass&)' is private [Error] within this context In function 'int main()': [Note] synthesized method 'MyClass::MyClass(const MyClass&)' first required here In member function 'MyClass& MyClass::operator=(const MyClass&)': [Error] 'DummyClass& DummyClass::operator=(const DummyClass&)' is private [Error] within this context In function 'int main()': [Note] synthesized method 'MyClass& MyClass::operator=(const MyClass&)' first required here
Updated on: 30-Jul-2019
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