noexcept operator (since C++11)

noexcept 运算符执行编译时检查，若表达式被声明为不抛出任何异常则返回 true 。

它可以在函数模板的 noexcept 说明符 中使用，用于声明该函数对于某些类型会抛出异常，而对于其他类型则不会。

语法

返回一个类型为 bool 的 纯右值 。若 表达式 的 潜在异常集合 为空 (C++17 前) 表达式 被指定为 不抛出 (C++17 起) ，则结果为 true ，否则为 false 。

expression 是一个 unevaluated operand 。

注释

即使 noexcept ( expr ) 为 true ，对 expr 的求值仍可能因遇到未定义行为而抛出异常。

关键词

noexcept

示例

#include <iostream>
#include <utility>
#include <vector>
void may_throw();
void no_throw() noexcept;
auto lmay_throw = []{};
auto lno_throw = []() noexcept {};
class T
{
public:
    ~T(){} // 析构函数阻止移动构造函数
           // 拷贝构造函数为 noexcept
};
class U
{
public:
    ~U(){} // 析构函数阻止移动构造函数
           // 拷贝构造函数为 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 <<
        "may_throw() is noexcept(" << noexcept(may_throw()) << ")\n"
        "no_throw() is noexcept(" << noexcept(no_throw()) << ")\n"
        "lmay_throw() is noexcept(" << noexcept(lmay_throw()) << ")\n"
        "lno_throw() is noexcept(" << noexcept(lno_throw()) << ")\n"
        "~T() is noexcept(" << noexcept(std::declval<T>().~T()) << ")\n"
        // 注意：以下测试还需要 ~T() 为 noexcept，因为
        // noexcept 内的表达式会构造并销毁临时对象
        "T(rvalue T) is noexcept(" << noexcept(T(std::declval<T>())) << ")\n"
        "T(lvalue T) is noexcept(" << noexcept(T(t)) << ")\n"
        "U(rvalue U) is noexcept(" << noexcept(U(std::declval<U>())) << ")\n"
        "U(lvalue U) is noexcept(" << noexcept(U(u)) << ")\n"
        "V(rvalue V) is noexcept(" << noexcept(V(std::declval<V>())) << ")\n"
        "V(lvalue V) is noexcept(" << noexcept(V(v)) << ")\n";
}

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

缺陷报告

下列行为变更缺陷报告被追溯应用于先前发布的C++标准。

参见