[問題] C++ Primer 4/e ch14問題

看板C_and_CPP (C/C++)作者Zephyr750 (紅蓮西風750)時間12年前 (2011/08/11 14:53)推噓0(0推 0噓 11→)

留言11則, 3人參與討論串1/1

使用平台：VC++6 //範例中沒有，隨意定義內容的Screen class class Screen { public: int a; }; class ScrPtr { friend class ScreenPtr; Screen *sp; size_t use; ScrPtr(Screen *p):sp(p), use(1){} ~ScrPtr(){delete sp;} }; class ScreenPtr { public: //沒有default建構式：ScreenPtrs必須綁定於某個物件上 ScreenPtr(Screen *p):ptr(new ScrPtr(p)){} //拷貝成員並累加參用計數 ScreenPtr(const ScreenPtr &orig):ptr(orig.ptr){ ++ptr->use; } ScreenPtr& operator=(const ScreenPtr&); //如果參用計數為0，刪除StrPtr物件 ~ScreenPtr(){ if(--ptr->use == 0) delete ptr; } → const Screen& operator*() const{ return *ptr->sp;} //錯誤訊息出現時指著這一行 const Screen* operator->() const{ return ptr->sp;} Screen& operator*(){ return *ptr->sp;} Screen* operator->(){ return ptr->sp;} private: ScrPtr *ptr;//指向被計數的ScrPtr }; error訊息： --------------------Configuration: ch14 - Win32 Debug-------------------- Compiling... main.cpp d:\c++primer4\ch14\screenptr.h(11) : error C2440: 'return' : cannot convert from 'class Screen' to 'const class ScreenPtr &' Reason: cannot convert from 'class Screen' to 'const class ScreenPtr' No constructor could take the source type, or constructor overload resolution was ambiguous d:\c++primer4\ch14\screenptr.h(12) : error C2440: 'return' : cannot convert from 'class Screen *' to 'const class ScreenPtr *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast d:\c++primer4\ch14\screenptr.h(13) : error C2440: 'return' : cannot convert from 'class Screen' to 'class ScreenPtr &' A reference that is not to 'const' cannot be bound to a non-lvalue d:\c++primer4\ch14\screenptr.h(14) : error C2440: 'return' : cannot convert from 'class Screen *' to 'class ScreenPtr *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast Error executing cl.exe. ch14.exe - 4 error(s), 0 warning(s) 請問是發生了什麼問題？？是不是const 的refrence和const的derefrence不可以放non-const呢？不過已經重載了，怎麼還會？？ -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 60.248.125.78 ※ 編輯: Zephyr750 來自: 60.248.125.78 (08/11 14:55) ※ 編輯: Zephyr750 來自: 60.248.125.78 (08/11 14:58)