std::move_if_noexcept

 

C++

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实用工具库

类型的支持 (basic types, RTTI, type traits)

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日期和时间

函数对象

initializer_list （C++11）

bitset

hash （C++11）

关系运算符 Original: Relational operators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

双和元组 Original: Pairs and tuples The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

pair

tuple （C++11）

piecewise_construct_t （C++11）

piecewise_construct （C++11）

掉期，远期和移动 Original: Swap, forward and move The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

swap

forward （C++11）

move （C++11）

move_if_noexcept （C++11）

declval （C++11）

 

Defined in header <utility>
template< class T > typename std::conditional<     !std::is_nothrow_move_constructible<T>::value && std::is_copy_constructible<T>::value,     const T&,     T&& >::type move_if_noexcept(T& x);		（C++11 起）

move_if_noexcept获得一个右值引用它的参数，如果它的移动构造函数不会抛出异常，否则得到一个左值，它的参数。它通常用于移动语义组合具有很强的异常保证.

Original:

move_if_noexcept obtains an rvalue reference to its argument if its move constructor does not throw exceptions, otherwise obtains an lvalue reference to its argument. It is typically used to combine move semantics with strong exception guarantee.

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例如，std::vector::resize偶尔会分配新的存储，然后移动或复制的元素从旧存储到新的存储。在此操作过程中如果发生异常，std::vector::resize撤消它所做的一切到这点，这是唯一可能std::move_if_noexcept来决定是否使用移动建设或拷贝构造.

Original:

For example, std::vector::resize occasionally allocates new storage and then moves or copies elements from old storage to new storage. If an exception occurs during this operation, std::vector::resize undoes everything it did to this point, which is only possible if std::move_if_noexcept was used to decide whether to use move construction or copy construction.

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参数

x

-

对象物的移动或复制 Original: the object to be moved or copied The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

返回值

std::move(x)或x，根据例外担保.

Original:

std::move(x) or x, depending on exception guarantees.

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例外

noexcept specification:  

noexcept

  （C++11 起）

为例

#include <iostream>
#include <utility>
 
struct Bad
{
    Bad() {}
    Bad(Bad&&)  // may throw
    {
        std::cout << "Throwing move constructor called\n";
    }
    Bad(const Bad&) // may throw as well
    {
        std::cout << "Throwing copy constructor called\n";
    }
};
 
struct Good
{
    Good() {}
    Good(Good&&) noexcept // will NOT throw
    {
        std::cout << "Non-throwing move constructor called\n";
    }
    Good(const Good&) {};
};
 
int main()
{
    Good g;
    Bad b;
    Good g2 = std::move_if_noexcept(g);
    Bad b2 = std::move_if_noexcept(b);
}

Output:

Non-throwing move constructor called
Throwing copy constructor called

复杂性

常数

Original:

Constant

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另请参阅

forward （C++11）	转发函数的参数 Original: forwards a function argument The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. （函数模板）
move （C++11）	获得一个右值引用 Original: obtains an rvalue reference The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. （函数模板）