C++ : noexcept (or throw()) virtual destructor = default;

Question

下面的代码是合法的吗？

class C
{
    virtual ~C() noexcept = default;
};

或

class C
{
    virtual ~C() throw() = default;
};

(throw() 已弃用，但我的编译器不支持 noexcept ;;)

Answer 1

8.4.2 [dcl.fct.def.default] An explicitly-defaulted function [...] may have an explicit exception-specification only if it is compatible (15.4) with the exception-specification on the implicit declaration.

15.4/3 [except.spec] Two exception-specifications are compatible if:

• both are non-throwing (see below), regardless of their form,
• both have the form noexcept(constant-expression) and the constant-expressions are equivalent, or
• both are dynamic-exception-specifications that have the same set of adjusted types.

因此，如果它与析构函数的隐式声明所具有的异常规范完全匹配，那么您只能给出一个显式的异常规范。

隐式析构函数的异常规范取决于它调用的函数:

15.4/14 [except.spec] An implicitly declared special member function shall have an exception-specification. If f is an implicitly declared [...] destructor, [...] its implicit exception-specification specifies the type-id T if and only if T is allowed by the exception-specification of a function directly invoked by f’s implicit definition; f shall allow all exceptions if any function it directly invokes allows all exceptions, and f shall allow no exceptions if every function it directly invokes allows no exceptions.

析构函数调用的函数是类的非静态数据成员、基类和虚拟基类的析构函数。

在您的情况下，由于该类没有数据成员和基类，因此它不调用任何函数，因此它属于最后一种情况。它直接调用的每个函数(没有)不允许有异常，所以这个析构函数必须不允许有异常。因此，您的异常规范必须是非抛出的，因此 nothrow、except() 和 exception(产生 true 的常量表达式)是您可以提供的唯一合适的异常规范，因此您的代码没有问题。