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noexcept 运算符 (C++11 起)

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异常规范
    noexcept 规范 (C++11)
    动态规范 (直到 C++17*)
noexcept 运算符 (C++11)
 

noexcept 运算符执行编译时检查,如果表达式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,以声明该函数对某些类型抛出异常,而对其他类型不抛出异常。

目录

[编辑] 语法

noexcept( expression )

返回类型为 boolprvalue。如果 expression潜在异常 集合为空(C++17 前)expression 被指定为 不抛出(C++17 起),结果为 true,否则为 false

expression 是一个 未求值操作数

如果 expression 是一个 prvalue,则应用 临时实体化

(C++17 起)

[编辑] 注意

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

如果 expression 是类类型或其(可能是多维)数组,临时实体化要求析构函数是非删除且可访问的。

(C++17 起)

[编辑] 关键词

noexcept

[编辑] 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(){} // dtor prevents move ctor
           // copy ctor is noexcept
};
 
class U
{
public:
    ~U(){} // dtor prevents move ctor
           // copy ctor is 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"
        // note: the following tests also require that ~T() is noexcept because
        // the expression within noexcept constructs and destroys a temporary
        "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";
}

输出

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)

[编辑] 缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告 应用于 发布时的行为 正确的行为
CWG 2722 C++17 不清楚是否应用临时实体化
如果 expression 是 prvalue
它被应用
在这种情况下
CWG 2792 C++11 要求 noexcept 运算符确定在遇到未定义行为时是否抛出异常
在遇到未定义行为时是否可能抛出异常
未要求

[编辑] 另请参阅

noexcept 说明符(C++11) 指定函数是否可能抛出异常[编辑]
动态异常规范(C++17 前) 指定函数抛出哪些异常 (C++11 中已弃用) [编辑]