C++单例模式实现（线程安全&支持多参数构造） C++单例模式实现（线程安全&支

C++单例模式实现（线程安全&支持多参数构造）线程安全版本

#include <>template class ThreadSafeSingleton { public: static T& get() { std::call_once(ThreadSafeSingleton::create_once_, &ThreadSafeSingleton::Create); return *ThreadSafeSingleton::instance_; } protected: static void Create() { instance_ = new T(); } static std::once_flag create_once_; static T* instance_; }; template std::once_flag ThreadSafeSingleton::create_once_; template T* ThreadSafeSingleton::instance_ = nullptr;

支持多参数版本的单例类

#include #include #include template class ThreadSafeSingleton {public: template static T& Getinstance(Args&&... args) { std::call_once(ThreadSafeSingleton::_call_once_flag, std::forward(&ThreadSafeSingleton::init), std::forward(args)...); return *ThreadSafeSingleton::m_instance; }private: ThreadSafeSingleton() = default; ~ThreadSafeSingleton() { delete ThreadSafeSingleton::m_instance; ThreadSafeSingleton::m_instance = nullptr; } ThreadSafeSingleton(const ThreadSafeSingleton& o) = delete; ThreadSafeSingleton& operator=(const ThreadSafeSingleton& o) = delete; template static void init(Args&&...args) { m_instance =new T(std::forward(args)...); }private: static std::once_flag _call_once_flag; static T* m_instance; }; template T* ThreadSafeSingleton::m_instance = nullptr; template std::once_flag ThreadSafeSingleton::_call_once_flag;

遇到问题点：

std::call_once中模板传参时候需要注意点：第二个参数为函数参数
std::forward<函数类型>(具体值)

【C++单例模式实现（线程安全&支持多参数构造）】std::forward(&ThreadSafeSingleton::init),
最后调用：

std::call_once(ThreadSafeSingleton::_call_once_flag,?std::forward(&ThreadSafeSingleton::init),?std::forward(args)...);

测试代码：

class TestSingleton1 { public: TestSingleton1(const std::string&){ std::cout << "lvalue" << std::endl; } TestSingleton1(std::string&&){ std::cout << "rvalue" << std::endl; } ~TestSingleton1() = default; void testFunc() { std::cout << "test function 1" << "\n"; } }; class TestSingleton2 { public: TestSingleton2(const std::string&){ std::cout << "lvalue" << std::endl; } TestSingleton2(std::string&&){ std::cout << "rvalue" << std::endl; } ~TestSingleton2() = default; void testFunc() { std::cout << "test function 2" << "\n"; } }; class TestSingleton3 { public: TestSingleton3(const std::string&,int i,double k){ std::cout << "lvalue" << std::endl; } ~TestSingleton3() = default; void testFunc() { std::cout << "test function 3" << "\n"; } }; int main(int argc, char **argv) { std::string str = "bb"; ThreadSafeSingleton::Getinstance(str).testFunc(); ThreadSafeSingleton::Getinstance(std::move(std::string("xxxx"))).testFunc(); ThreadSafeSingleton::Getinstance("yyyy",1,2.0).testFunc(); return 0 }

本文代码参考
《深入应用C++11》