If you are a C++ programmer, you may have come across the term "implicitly-deleted copy constructor." This term refers to a situation where the compiler generates a copy constructor for a class, but the copy constructor is deleted. This guide will help you understand what an implicitly-deleted copy constructor is, why it is generated, and how to handle it.
What is an Implicitly-Deleted Copy Constructor?
An implicitly-deleted copy constructor is a copy constructor that is generated by the compiler but is not available for use. The copy constructor is generated as part of the compiler's default behavior when a copy constructor is not explicitly defined for a class. However, the generated copy constructor is deleted because the class has a member that cannot be copied.
Why is an Implicitly-Deleted Copy Constructor Generated?
An implicitly-deleted copy constructor is generated when a class has a member that cannot be copied. This can occur when the class has a member that is a reference or a const object. In these cases, the compiler cannot generate a copy constructor because it cannot copy the member.
How to Handle an Implicitly-Deleted Copy Constructor
To handle an implicitly-deleted copy constructor, you can either define a copy constructor for the class or make the class member that cannot be copied movable. If you define a copy constructor for the class, you can use it to copy the class without copying the member that cannot be copied. If you make the class member movable, the compiler can generate a move constructor that can move the member instead of copying it.
Example Code
Here is an example of a class that has an implicitly-deleted copy constructor:
class MyClass {
public:
MyClass(const int& ref) : m_ref(ref) {}
private:
const int& m_ref;
};
In this example, the class MyClass has a member m_ref that is a reference. Because the member is a reference, the compiler cannot generate a copy constructor for the class. Therefore, the copy constructor is implicitly deleted.
To handle this situation, you can define a copy constructor for the class that does not copy the member m_ref:
class MyClass {
public:
MyClass(const int& ref) : m_ref(ref) {}
MyClass(const MyClass& other) : m_ref(other.m_ref) {}
private:
const int& m_ref;
};
In this example, the copy constructor for MyClass is defined to copy the member m_ref from the object other.
FAQ
Q1: What is a copy constructor in C++?
A copy constructor is a special constructor in C++ that is used to create a new object as a copy of an existing object.
Q2: When is a copy constructor called in C++?
A copy constructor is called when a new object is created as a copy of an existing object, either explicitly or implicitly.
Q3: What is a deleted function in C++?
A deleted function is a function that is declared but not defined, and cannot be called. This is useful for preventing certain types of function calls that are not desired.
Q4: What is a const object in C++?
A const object in C++ is an object that cannot be modified after it is created. This is useful for preventing unintended changes to objects.
Q5: What is a reference in C++?
A reference in C++ is an alias for an existing object. References are useful for passing objects by reference instead of by value, which can improve performance and reduce memory usage.