vtable

Number of Virtual tables and Virtual Pointers in a C++ Program

由 生来就可爱ヽ(ⅴ＜●) 提交于 2019-11-27 01:41:24
问题 Let say we have below program: class A { public: virtual fun(){}; }; class B:public A { public: virtual fun(){}; }; int main() { A a1; B b1; } My question is how many vtables and how many vptrs will be created, when we run this program? 回答1: Its heavily implementation dependent, but generally you'll get one vtable object per class that has any virtual functions (classes with no virtual functions or bases don't need them), and one vptr per object of a class with a vtable (pointing at the class

C++ Undefined Reference to vtable and inheritance

由 蹲街弑〆低调 提交于 2019-11-27 01:18:14
File A.h #ifndef A_H_ #define A_H_ class A { public: virtual ~A(); virtual void doWork(); }; #endif File Child.h #ifndef CHILD_H_ #define CHILD_H_ #include "A.h" class Child: public A { private: int x,y; public: Child(); ~Child(); void doWork(); }; #endif And Child.cpp #include "Child.h" Child::Child(){ x = 5; } Child::~Child(){...} void Child::doWork(){...}; The compiler says that there is a undefined reference to vtable for A . I have tried lots of different things and yet none have worked. My objective is for class A to be an Interface, and to seperate implementation code from headers. Alok

Where in memory is vtable stored?

由 自古美人都是妖i 提交于 2019-11-26 22:45:34
问题 Where in memory is vtable stored? 回答1: Depends on compiler. In VC++, the vtable pointer stored at the beginning of the object allocation, before any member data. (Provided your class has at least one virtual member function.) There also may be multiple vtable pointers, if your class multiply-inherits from other classes with vtables. The vtables themselves are statically allocated somewhere in your address space. Then the object layout looks like (for an instance of C): A's VTable ptr A's

undefined reference to vtable [duplicate]

由 ↘锁芯ラ 提交于 2019-11-26 21:42:04
问题 This question already has an answer here: Undefined reference to vtable 28 answers i have a class afporoills that helps find data in our memory managment module. (dont ask why such a wierd name i have no idea) class afporoills{ void** test(int pos); }; void** afporoills::test(int pos){ int x=(pos<<3)|1023*x; void** ret=(void**)x; if((int)ret%16) return this.test(pos+1); void* (*fp)(float, uint16__t)=x; ret=ret+(*fp)(1.0f, (uint16__t)pos); return ret; } int test(){ afporoills afporoills14;

What is Vtable in C++ [duplicate]

由 陌路散爱 提交于 2019-11-26 19:53:12
问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: why do I need virtual table? What is vtAble in C++? Got to know vtable is a virtual table which has an array of pointers to virtual functions. Is there an article with practical implementation? (Any walk through will be appreciated) 回答1: V-tables (or virtual tables) are how most C++ implementations do polymorphism. For each concrete implementation of a class, there is a table of function pointers to all the

Can't downcast because class is not polymorphic?

由 人走茶凉 提交于 2019-11-26 19:48:29
问题 Is it possible to have inheritance with no virtual methods? The compiler is saying that the following code is not polymorphic. Example: Class A(){ int a; int getA(){return a;}; } Class B(): A(){ int b; int getB(){return b;}; } In another class we are trying to downcast from an A object to a B object: A *a; B *b = dynamic_cast<B*>(a) but this gives the following error: cannot dynamic_cast ... (source type is polymorphic) 回答1: Syntax errors non-withstanding, you cannot dynamic_cast a non

Qt: Signals and slots Error: undefined reference to `vtable for

由 牧云@^-^@ 提交于 2019-11-26 18:28:48
问题 Following example from this link: http://developer.kde.org/documentation/books/kde-2.0-development/ch03lev1sec3.html #include <QObject> #include <QPushButton> #include <iostream> using namespace std; class MyWindow : public QWidget { Q_OBJECT // Enable slots and signals public: MyWindow(); private slots: void slotButton1(); void slotButton2(); void slotButtons(); private: QPushButton *button1; QPushButton *button2; }; MyWindow :: MyWindow() : QWidget() { // Create button1 and connect button1-

What is the VTT for a class?

由 拈花ヽ惹草 提交于 2019-11-26 17:34:55
问题 Recently ran across a C++ linker error that was new to me. libfoo.so: undefined reference to `VTT for Foo' libfoo.so: undefined reference to `vtable for Foo' I recognized the error and fixed my problem, but I still have a nagging question: what exactly is a VTT? Aside: For those interested, the problem occurs when you forget to define the first virtual function declared in a class. The vtable goes into the compilation unit of the class's first virtual function. If you forget to define that

What is the first (int (*)(…))0 vtable entry in the output of g++ -fdump-class-hierarchy?

由 不问归期 提交于 2019-11-26 17:07:56
For this code: class B1{ public: virtual void f1() {} }; class D : public B1 { public: void f1() {} }; int main () { B1 *b1 = new B1(); D *d = new D(); return 0; } After compilation, the vtable I get with g++ -fdump-class-hierarchy is: Vtable for B1 B1::_ZTV2B1: 3u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI2B1) 16 B1::f1 Vtable for D D::_ZTV1D: 3u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI1D) 16 D::f1 I failed to understand what do the entries like (int ( )(...))0* correspond to. Of course it means something like, it is a function which returns an int and takes unlimited number

Q_OBJECT throwing 'undefined reference to vtable' error [duplicate]

由 喜你入骨 提交于 2019-11-26 16:01:42
This question already has an answer here: Qt Linker Error: “undefined reference to vtable” [duplicate] 9 answers I'm using Qt Creator 2.0.1 with Qt 4.7.0 (32 bit) on Windows 7 Ultimate 32 bit. Consider the following code, which is a minimum to produce the error: class T : public QObject, public QGraphicsItem { Q_OBJECT public: T() {} QRectF boundingRect() const {return QRectF();} void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {} }; int main() { T t; return 0; } The above code fragment causes the following linker errors: In function `T': undefined
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