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https://github.com/changkun/modern-cpp-tutorial.git
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67 lines
2.3 KiB
C++
67 lines
2.3 KiB
C++
#include <iostream>
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#include <memory>
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void foo(std::shared_ptr<int> i)
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{
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(*i)++;
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}
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//struct Base {
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// Base() { std::cout << " Base::Base()\n"; }
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// ~Base() { std::cout << " Base::~Base()\n"; }
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//};
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//
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//struct Subclass: public Base {
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// Subclass() { std::cout << " Subclass::Subclass()\n"; }
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// ~Subclass() { std::cout << " Subclass::~Subclass()\n"; }
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//};
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//
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//void thr(std::shared_ptr<Base> p)
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//{
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// std::this_thread::sleep_for(std::chrono::seconds(1));
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// std::shared_ptr<Base> lp = p; // 即使引用计数增加也是线程安全的
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// {
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// static std::mutex io_mutex;
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// std::lock_guard<std::mutex> lk(io_mutex);
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// std::cout << "local pointer in a thread:\n"
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// << " lp.get() = " << lp.get()
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// << ", lp.use_count() = " << lp.use_count() << '\n';
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// }
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//}
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int main()
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{
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// auto pointer = new int(10); // 非法, 不允许直接赋值
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// 构造了一个 std::shared_ptr
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auto pointer = std::make_shared<int>(10);
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auto pointer2 = pointer; // 引用计数+1
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auto pointer3 = pointer; // 引用计数+1
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foo(pointer);
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std::cout << *pointer << std::endl; // 11
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int *p = pointer.get(); // 这样不会增加引用计数
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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pointer2.reset();
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std::cout << "reset pointer2:" << std::endl;
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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pointer3.reset();
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std::cout << "reset pointer3:" << std::endl;
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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// std::cout << *pointer << std::endl; // 引用计数为0时, 非法访问
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// 离开作用域前，pointer 会被析构，引用计数减为0, 从而释放内存
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return 0;
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}
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