Do you want to learn about deleted implicitly declared destructor in a C++ app? Do you know what kind of methods we have that we can declare and use to deleted implicitly-defined destructors? What is defaulted destructor? In this post, we will try to explain deleted implicitly declared destructors in Classes with given examples.
What does a Constructor mean in a C++ app?
The Constructor in C++ is a function, a method in the class, but it is a ‘special method’ that is automatically called when an object of a class is created. We don’t need to call this function. Whenever a new object of a class is created, the Constructor allows the class to initialize member variables or allocate storage. This is why the name Constructor is given to this special method. Here is a simple constructor class example below,
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class myclass { public: myclass() { std::cout << "myclass is constructed!\n"; }; }; |
What does a Destructor mean in a C++ app?
The Destructor in classes (i.e class_name) is a special member function to delete objects, in other words it is called when the lifetime of an object ends. The purpose of the destructor is to do operations when destruct the object. The object may have acquired or allocated data on memory on runtime, they need to be freed too when objects are being deleted, destructor is the function that frees the resources of the object. When we construct an object, sometimes we need operations to deconstruct. Destructors are not only used in classes but also used with struct and union data types.
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class myclass { public: ~myclass() // Destructor { }; }; |
What is a deleted implicitly-declared destructor in C++?
The implicitly-declared or defaulted destructor for the class is a destructor method that it is defined as deleted since C++11. To say that is a Implicitly Declared Destructor, any of the following below should be maintained,
- The class has a non-static data member that cannot be destructed
- The class has direct or virtual base class that cannot be destructed
- The class is a union and has a variant member with non-trivial destructor
also note that,
- If the base class has a virtual destructor then implicitly-declared destructor is virtual
- A defaulted prospective destructor for the class is defined as deleted if it is not the destructor for that class
According to open-std.org resource, any direct or virtual base class or non-static data member has a type with a destructor that is deleted or inaccessible from the defaulted default constructor or default constructor.
Here is an Implicitly-Declared Default Constructor example that gives an Error,
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#include <iostream> class my_class { public: ~my_class() = delete; // Destructor that is deleted }; class my_otherclass : public my_class { public: // This class has Deleted Implicitly-Declared Destructor }; int main() { my_otherclass class1; // ERROR: default constructor of 'my_otherclass' is implicitly deleted because base class 'my_class' has a deleted destructor class1.~my_otherclass(); // Calling a Implicitly-Declared Destructor getchar(); return 0; } |
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