noexcept 运算符 (C++11 起)

 

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技术规范

 

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异常

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noexcept 指定符(C++11)

noexcept 运算符(C++11)

动态异常规定(C++20 前)

 

noexcept 运算符进行编译时检查，若表达式声明为不抛出任何异常则返回 true 。

它可用于函数模板的 noexcept 指定符以声明函数将对某些类型抛出异常，但不对其他类型抛出。

语法

noexcept( expression )

返回 bool 类型的纯右值。

解释

noexcept 运算符不对 expression 求值。

若 expression 含有至少一个下列潜在求值的构造则结果为 false ： 调用无不抛出异常指定的任意类型函数，除非它是常量表达式。 throw 表达式。 目标类型是引用类型，且转换需要运行时检查时的 dynamic_cast 表达式 参数类型是多态类类型的 typeid 表达式 所有其他情况下结果是 true 。	(C++17 前)
若 expression 的潜在异常集合为空则结果为 true ，否则为 false 。	(C++17 起)

关键词

noexcept

示例

运行此代码

#include <iostream>
#include <utility>
#include <vector>
 
void may_throw();
void no_throw() noexcept;
auto lmay_throw = []{};
auto lno_throw = []() noexcept {};
class T{
public:
  ~T(){} // 析构函数防止移动构造函数
         // 复制构造函数是 noexcept
};
class U{
public:
  ~U(){} // 析构函数防止移动构造函数
         // 复制构造函数是 noexcept(false)
  std::vector<int> v;
};
class V{
public:
  std::vector<int> v;
};
 
int main()
{
 T t;
 U u;
 V v;
 
 std::cout << std::boolalpha
           << "Is may_throw() noexcept? " << noexcept(may_throw()) << '\n'
           << "Is no_throw() noexcept? " << noexcept(no_throw()) << '\n'
           << "Is lmay_throw() noexcept? " << noexcept(lmay_throw()) << '\n'
           << "Is lno_throw() noexcept? " << noexcept(lno_throw()) << '\n'
           << "Is ~T() noexcept? " << noexcept(std::declval<T>().~T()) << '\n'
           // note: the following tests also require that ~T() is noexcept because
           // the expression within noexcept constructs and destroys a temporary
           << "Is T(rvalue T) noexcept? " << noexcept(T(std::declval<T>())) << '\n'
           << "Is T(lvalue T) noexcept? " << noexcept(T(t)) << '\n'
           << "Is U(rvalue U) noexcept? " << noexcept(U(std::declval<U>())) << '\n'
           << "Is U(lvalue U) noexcept? " << noexcept(U(u)) << '\n'  
           << "Is V(rvalue V) noexcept? " << noexcept(V(std::declval<V>())) << '\n'
           << "Is V(lvalue V) noexcept? " << noexcept(V(v)) << '\n';  
}

输出：

Is may_throw() noexcept? false
Is no_throw() noexcept? true
Is lmay_throw() noexcept? false
Is lno_throw() noexcept? true
Is ~T() noexcept? true
Is T(rvalue T) noexcept? true
Is T(lvalue T) noexcept? true
Is U(rvalue U) noexcept? false
Is U(lvalue U) noexcept? false
Is V(rvalue V) noexcept? true
Is V(lvalue V) noexcept? false

参阅

noexcept 指定符	要求函数不抛出任何异常 (C++11)
异常规定	指定函数所抛出的异常 (弃用)