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std::shared_ptr::use_count

STD：：共享[医]PTR：：使用[医]数数

long use_count() const;​​

返回不同shared_ptr实例%28this包括%29管理当前对象。如果没有托管对象，​0​会被归还。

在多线程环境中，使用返回的值。[医]计数大约为%28，典型实现使用记忆[医]命令[医]放松加载%29。

参数

%280%29

返回值

的数目shared_ptr实例管理当前对象或​0​如果没有托管对象。

例外

noexcept规格：

noexcept

注记

常见用例包括。

  • 与...比较​0​.如果use_count返回零，共享指针为空空并且不管理对象%28，无论其存储的指针是否为空%29。但是，这在多线程环境中并不能得到保证。

  • 与...比较1.如果use_count返回1，没有其他所有者，这可能表明托管对象是安全的修改。成员函数unique()是为这个用例提供的。但是，这在多线程环境中并不能得到保证。

例

二次

#include <memory> 
#include <iostream> 
 
void fun(std::shared_ptr<int> sp)
{
    std::cout << "fun: sp.use_count() == " << sp.use_count() << '\n'; 
}
 
int main() 
{ 
    auto sp1 = std::make_shared<int>(5
    std::cout << "sp1.use_count() == " << sp1.use_count() << '\n'; 
 
    fun(sp1
}

二次

产出：

二次

sp1.use_count() == 1
fun: sp.use_count() == 2

二次

另见

unique (deprecated)checks whether the managed object is managed only by the current shared_ptr instance (public member function)

 © cppreference.com

在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/Memory/Shared[医]PTR/使用[医]数数

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