Special Member Functions - Example

Example

The following example depicts two classes: Explicit for which all C++98 special member functions are explicitly declared and Implicit for which none are declared.

#include class Explicit { friend class Implicit; string msg; public: Explicit : msg("") { std::cout << "Default constructor " << msg << '\n'; } Explicit(const string& value) : msg(value) { std::cout << "Non-default constructor " << msg << '\n'; } Explicit(const Explicit& other) : msg(other.msg) { std::cout << "Copy constructor " << msg << '\n'; } Explicit& operator=(const Explicit& other) { std::cout << "Copy assignment operator " << msg << '\n'; if (this != &other) { msg = other.msg; } return *this; } ~Explicit { std::cout << "Destructor " << msg << '\n'; } }; class Implicit : public Explicit { int i; void* p; Explicit member; public: void Spew { std::cout << "Implicit(" << msg << ", " << member.msg << ")\n"; } };

In this case the class Implicit has not explicitly defined the destructor and the compiler will create a destructor equivalently to this:

// Sub-objects are destroyed in the opposite order to their construction Implicit::~Implicit { member.~Explicit; // destroy member (void)p; // do nothing for p, void* has no destructor (void)i; // do nothing for i, int has no destructor ~Explicit; // call the base class's destructor }

Read more about this topic:  Special Member Functions

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