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In C++11, defaulted and deleted functions give you explicit control over whether the special member functions are automatically generated. Deleted functions also give you simple language to prevent problematic type promotions from occurring in arguments to functions of all types—special member functions, as well as normal member functions and non-member functions—which would otherwise cause an unwanted function call.

In C++, the compiler automatically generates the default constructor, copy constructor, copy-assignment operator, and destructor for a type if it does not declare its own. These functions are known as the *special member functions*, and they are what make simple user-defined types in C++ behave like structures do in C. That is, you can create, copy, and destroy them without any additional coding effort. C++11 brings move semantics to the language and adds the move constructor and move-assignment operator to the list of special member functions that the compiler can automatically generate.

The consequences of these rules can also leak into object hierarchies. For example, if for any reason a base class fails to have a default constructor that's callable from a deriving class—that is, a **`public`** or **`protected`** constructor that takes no parameters—then a class that derives from it cannot automatically generate its own default constructor.

These rules can complicate the implementation of what should be straight-forward, user-defined types and common C++ idioms—for example, making a user-defined type non-copyable by declaring the copy constructor and copy-assignment operator privately and not defining them.

- Explicitly defaulted special member functions are still considered trivial, so there is no performance penalty, and `noncopyable` is not prevented from being a true POD type.

- The copy constructor and copy-assignment operator are public but deleted. It is a compile-time error to define or call a deleted function.

Similar idioms exist for making user-defined types that are non-movable, that can only be dynamically allocated, or that cannot be dynamically allocated. Each of these idioms have pre-C++11 implementations that suffer similar problems, and that are similarly resolved in C++11 by implementing them in terms of defaulted and deleted special member functions.

You can default any of the special member functions—to explicitly state that the special member function uses the default implementation, to define the special member function with a non-public access qualifier, or to reinstate a special member function whose automatic generation was prevented by other circumstances.

You can delete special member functions as well as normal member functions and non-member functions to prevent them from being defined or called. Deleting of special member functions provides a cleaner way of preventing the compiler from generating special member functions that you don't want. The function must be deleted as it is declared; it cannot be deleted afterwards in the way that a function can be declared and then later defaulted.

Deleting of normal member function or non-member functions prevents problematic type promotions from causing an unintended function to be called. This works because deleted functions still participate in overload resolution and provide a better match than the function that could be called after the types are promoted. The function call resolves to the more-specific—but deleted—function and causes a compiler error.

This **`__declspec`** attribute tells the compiler that a function does not return. As a consequence, the compiler knows that the code following a call to a **`__declspec(noreturn)`** function is unreachable.

If the compiler finds a function with a control path that does not return a value, it generates a warning (C4715) or error message (C2202). If the control path cannot be reached due to a function that never returns, you can use **`__declspec(noreturn)`** to prevent this warning or error.

In the following sample,the **`else`** clause does not contain a return statement. Declaring `fatal` as **`__declspec(noreturn)`** avoids an error or warning message.

__declspec(noreturn) extern void fatal () {}

int main() {

if(1)

return 1;

else if(0)

return 0;

else

fatal();