最令人烦恼的parsing

我从这里得到了代码。

class Timer { public: Timer(); }; class TimeKeeper { public: TimeKeeper(const Timer& t); int get_time() { return 1; } }; int main() { TimeKeeper time_keeper(Timer()); return time_keeper.get_time(); } 

从它的外观来看，它应该得到编译错误，由于行：

 TimeKeeper time_keeper(Timer()); 

但只有在return time_keeper.get_time(); 存在。

为什么这一行甚至是重要的，编译器会在time_keeper(Timer() )构造上time_keeper(Timer() )歧义。

Answer 1

这是由于TimeKeeper time_keeper(Timer()); 被解释为函数声明而不是variables定义。 这本身并不是错误，但是当您尝试访问time_keeper（这是一个函数，而不是TimeKeeper实例）的get_time()成员时，编译器会失败。

这就是你的编译器如何查看代码：

 int main() { // time_keeper gets interpreted as a function declaration with a function argument. // This is definitely *not* what we expect, but from the compiler POV it's okay. TimeKeeper time_keeper(Timer (*unnamed_fn_arg)()); // Compiler complains: time_keeper is function, how on earth do you expect me to call // one of its members? It doesn't have member functions! return time_keeper.get_time(); }