最令人頭疼的解析

Question

我從here得到的代碼。

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(); 
} 

從外觀上來看，它應該得到編譯錯誤，由於行：

TimeKeeper time_keeper(Timer()); 

但如果return time_keeper.get_time();出現時，它纔會發生。

爲什麼這條線甚至有問題，編譯器會在time_keeper(Timer())構造中發現模糊性。

Answer 1

這是由於TimeKeeper time_keeper(Timer());被解釋爲函數聲明而不是變量定義。這本身並不是錯誤，但當您嘗試訪問time_keeper（這是一個函數，而不是TimeKeeper實例）的get_time()成員時，編譯器會失敗。

這是你的編譯器如何查看代碼：[？爲什麼會出現在構造函數中沒有呼叫]

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(); 
}