最令人头疼的解析

Question

我从here得到的代码。

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(); 
} 

从外观上来看，它应该得到编译错误，由于行：

TimeKeeper time_keeper(Timer()); 

但如果return time_keeper.get_time();出现时，它才会发生。

为什么这条线甚至有问题，编译器会在time_keeper(Timer())构造中发现模糊性。

Answer 1

这是由于TimeKeeper time_keeper(Timer());被解释为函数声明而不是变量定义。这本身并不是错误，但当您尝试访问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。

这是你的编译器如何查看代码：[？为什么会出现在构造函数中没有呼叫]

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(); 
}