std::weak_ptr::lock
std::shared_ptr<T> lock() const; | | (since C++11) |
|---|
创建一个新的std::shared_ptr它共享托管对象的所有权。如果没有托管对象，即*this是空的，那么返回的shared_ptr也是空的。
有效回报expired() ? shared_ptr<T>() : shared_ptr<T>(*this)被原子处决。
参数
%280%29
返回值
阿shared_ptr在以下情况下，哪个共享拥有的对象的所有权？std::weak_ptr::expired回报false.否则返回默认构造的shared_ptrT型。
例外
noexcept规格：
noexcept
注记
函数和std::shared_ptr可用于获取由std::weak_ptr的不同之处在于std::shared_ptr抛出异常时，std::weak_ptr参数为空，而std::weak_ptr<T>::lock()构造空std::shared_ptr<T>...
例
二次
#include <iostream>
#include <memory>
void observe(std::weak_ptr<int> weak)
{
if (auto observe = weak.lock()) {
std::cout << "\tobserve() able to lock weak_ptr<>, value=" << *observe << "\n";
} else {
std::cout << "\tobserve() unable to lock weak_ptr<>\n";
}
}
int main()
{
std::weak_ptr<int> weak;
std::cout << "weak_ptr<> not yet initialized\n";
observe(weak);
{
auto shared = std::make_shared<int>(42);
weak = shared;
std::cout << "weak_ptr<> initialized with shared_ptr.\n";
observe(weak);
}
std::cout << "shared_ptr<> has been destructed due to scope exit.\n";
observe(weak);
}二次
产出：
二次
weak_ptr<> not yet initialized
observe() unable to lock weak_ptr<>
weak_ptr<> initialized with shared_ptr.
observe() able to lock weak_ptr<>, value=42
shared_ptr<> has been destructed due to scope exit.
observe() unable to lock weak_ptr<>二次
缺陷报告
以下行为更改缺陷报告追溯应用于先前发布的C++标准。
DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
LWG 2316 | C++11 | lock() was not required to be atomic, but required to be noexcept, which led to a contradiction | specified to be atomic |
另见
expired | checks whether the referenced object was already deleted (public member function) |
|---|
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