C++ 带括号的取消引用(带迭代器)

Question

我的问题很简单。我有一个值 vector (这里是线程，无关紧要)，我想遍历它们。但是，有两个版本的代码对我来说看起来相同，但只有第二个版本有效。我想知道为什么。

版本 1 (不编译)

int main(){
    int someValue = 5;
    vector<std::thread *> threadVector;

    threadVector.resize(20);

    for (int i = 0; i < 20; i++) {
        threadVector[i] = new std::thread(foo, std::ref(someValue));
    }

    for (std::vector<std::thread *>::iterator it = threadVector.begin(); it != threadVector.end(); ++it) {
        *it->join(); // *********Notice this Line*********
    }

    system("pause"); // I know I shouldn't be using this
}

版本 2 (有效)

int main(){
    int someValue = 5;
    vector<std::thread *> threadVector;

    threadVector.resize(20);

    for (int i = 0; i < 20; i++) {
        threadVector[i] = new std::thread(foo, std::ref(someValue));
    }

    for (std::vector<std::thread *>::iterator it = threadVector.begin(); it != threadVector.end(); ++it) {
        (*it)->join(); // *********Notice this Line*********
    }

    system("pause"); // I know I shouldn't be using this
}

Answer 1

这是操作顺序的问题。

*it->join();

解析为:

*(it->join());