Every non-static member of class type has a trivial default constructorĪ trivial default constructor is a constructor that performs no action.Every direct base of T has a trivial default constructor.T has no non-static members with brace-or-equal initializers.The constructor is not user-provided (that is, implicitly-defined or defaulted). performs no action) if all of the following is true: The default constructor for class T is trivial (i.e. T is a union and all of its variant members are const.T is a union with at least one variant member with non-trivial default constructor.T has a direct or virtual base which has a deleted destructor, or a destructor that is inaccessible from this constructor.T has a direct or virtual base which has a deleted default constructor, or it is ambiguous or inaccessible from this constructor.T has a member (without a brace-or-equal initializer) (since C++11), which has a deleted default constructor, or its default constructor is ambiguous or inaccessible from this constructor.T has a const member without user-defined default constructor or a brace-or-equal initializer (since C++11).T has a member of reference type without a brace-or-equal initializer.The implicitly-declared or defaulted default constructor for class T is undefined (until C++11) defined as deleted (since C++11) if any of the following is true: Deleted implicitly-declared default constructor That is, it calls the default constructors of the bases and of the non-static members of this class. If the implicitly-declared default constructor is not deleted or trivial, it is defined (that is, a function body is generated and compiled) by the compiler, and it has exactly the same effect as a user-defined constructor with empty body and empty initializer list. If some user-defined constructors are present, the user may still force the generation of the implicitly declared constructor with the keyword default If no user-defined constructors of any kind are provided for a class type ( struct, class, or union), the compiler will always declare a default constructor as an inline public member of its class. The default constructors are called during default initializations and value initializations. 4) Explicitly forcing the automatic generation of a default constructorĬlassName is the identifier of the enclosing class
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