Re: [翻譯] Rvalue References: C++0x Features in …

看板C_and_CPP作者fuha (mimi)時間14年前 (2010/05/03 17:33)推噓0(0推 0噓 0→)

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回一下這篇翻譯的文章~ 不知道大家有沒有試過這個範例~ 在講 move semantics: moving from lvalues 要把 lvalue 轉成 rvalue 會有編譯錯誤~ 自己試試看改了很久還是改不出來所以問一下有認真看這篇文章的板友我是用 VC 2010 Express 4.0.30319 RTMRel ~ 錯誤訊息是 error C2440: 'return' : cannot convert from 'remote_integer' to 'remote_integer &&' You cannot bind an lvalue to an rvalue reference Test2010.cpp(49) : see reference to function template instantiation 'remote_integer &&nMove<remote_integer&>(T)' being compiled with [ T=remote_integer & ] 既然 T 已經是　remote_integer & 型別但是會有 cannot convert from 'remote_integer' to 'remote_integer &&' 的錯誤真的頭大~ : #include <stddef.h> : #include <iostream> : #include <ostream> : using namespace std; : template <typename T> struct RemoveReference { : typedef T type; : }; : template <typename T> struct RemoveReference<T&> { : typedef T type; : }; : template <typename T> struct RemoveReference<T&&> { : typedef T type; : }; : template <typename T> typename RemoveReference<T>::type&& Move(T&& t) { : return t; : } : class remote_integer { : public: : remote_integer() { : cout << "Default constructor." << endl; : m_p = NULL; : } : explicit remote_integer(const int n) { : cout << "Unary constructor." << endl; : m_p = new int(n); : } : remote_integer(const remote_integer& other) { : cout << "Copy constructor." << endl; : m_p = NULL; : *this = other; : } : #ifdef MOVABLE : remote_integer(remote_integer&& other) { : cout << "MOVE CONSTRUCTOR." << endl; : m_p = NULL; : *this = Move(other); // RIGHT : } : #endif // #ifdef MOVABLE : remote_integer& operator=(const remote_integer& other) { : cout << "Copy assignment operator." << endl; : if (this != &other) { : delete m_p; : if (other.m_p) { : m_p = new int(*other.m_p); : } else { : m_p = NULL; : } : } : return *this; : } : #ifdef MOVABLE : remote_integer& operator=(remote_integer&& other) { : cout << "MOVE ASSIGNMENT OPERATOR." << endl; : if (this != &other) { : delete m_p; : m_p = other.m_p; : other.m_p = NULL; : } : return *this; : } : #endif // #ifdef MOVABLE : ~remote_integer() { : cout << "Destructor." << endl; : delete m_p; : } : int get() const { : return m_p ? *m_p : 0; : } : private: : int * m_p; : }; : remote_integer frumple(const int n) { : if (n == 1729) { : return remote_integer(1729); : } : remote_integer ret(n * n); : return ret; : } : int main() { : remote_integer x = frumple(5); : cout << x.get() << endl; : remote_integer y = frumple(1729); : cout << y.get() << endl; : } : C:\Temp>cl /EHsc /nologo /W4 /O2 /DMOVABLE unified_right.cpp : unified_right.cpp : C:\Temp>unified_right : Unary constructor. : MOVE CONSTRUCTOR. : MOVE ASSIGNMENT OPERATOR. : Destructor. : 25 : Unary constructor. : 1729 : Destructor. : Destructor. Test2010.cpp(19) : error C2440: 'return' : cannot convert from 'remote_integer' to 'remote_integer &&' You cannot bind an lvalue to an rvalue reference Test2010.cpp(49) : see reference to function template instantiation 'remote_integer &&nMove<remote_integer&>(T)' being compiled with [ T=remote_integer & ] -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 59.120.189.231 ※ 編輯: fuha 來自: 59.120.189.231 (05/03 17:35)

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