线程在构造关联的线程对象时立即开始执行(等待任何OS调度延迟),从提供给作为构造函数参数的顶层函数开始。顶层函数的返回值将被忽略,而且若它以抛异常终止,则调用std::terminate。顶层函数可以通过std::promise或通过修改共享变量(可能需要同步,见std::mutex与std::atomic)将其返回值或异常传递给调用方。
它用于创建一个对象的引用包装器(reference wrapper),这个引用包装器可以被传递给函数或者存储在容器中。具体来说,std::ref 可以用来避免对象的拷贝,并确保传递的是对象的引用,而不是对象的副本。 std::ref 的使用场景 函数参数传递:在某些情况下,我们希望将对象的引用而不是对象本身传递给函数,避免不必要的拷贝...
(std::chrono::milliseconds(10)); } } int main() { int n = 0; std::thread t1; // t1 is not a thread std::thread t2(f1, n + 1); // pass by value std::thread t3(f2, std::ref(n)); // pass by reference std::thread t4(std::move(t3)); // t4 is now running f2(...
std::ref(n));// pass by referencestd::threadt4(std::move(t3));// t4 is now running f2(). t3 is no longer a threadstd::threadt5(&foo::bar, &f);// t5 runs foo::bar() on object fstd::threadt6(b);// t6 runs baz::operator() on object bt2.join()...
thread 是模板，参数的形式是所谓的 forwarding reference(或 universal reference)，所以传参给 thread 的...
(std::chrono::milliseconds(10)); } } int main() { int n = 0; std::thread t1; // t1 is not a thread std::thread t2(f1, n + 1); // pass by value std::thread t3(f2, std::ref(n)); // pass by reference std::thread t4(std::move(t3)); // t4 is now running f2(...
std::thread t1;//t1 is not represent a threadstd::thread t2(func1, arg +1);//pass to thread by valuestd::thread t3(func2, std::ref(arg));//pass to thread by referencestd::thread t4(std::move(t3));//t4 is now running func2(). t3 is no longer a thread//t1.join() Erro...
(std::chrono::milliseconds(10)); } } int main() { int n = 0; std::thread t1; // t1 is not a thread std::thread t2(f1, n + 1); // pass by value std::thread t3(f2, std::ref(n)); // pass by reference std::thread t4(std::move(t3)); // t4 is now running f2(...
reference_wrapper通过使用std::ref显式初始化线程:auto thread1 = std::thread(SimpleThread, std::ref(a));(或std::cref代替std::ref,视情况而定)。根据cppreference中的std:thread注释:线程函数的参数按值移动或复制。如果需要将引用参数传递给线程函数,则必须将其包装(例如,使用std::ref或std::cref)。
为了解决这些问题，C++ 标准库提供了三个有用的工具：std::cref、std::ref 和 std::reference_...