D指针和Q指针

通过多方查阅资料，普遍认为Qt引入D指针和Q指针一方面是为了数据封装实现隐藏，另一方面是为了解决二进制兼容问题，避免因改变类的私有数据重新编译库的问题。

d_ptr.h

#ifndef D_PTR_H#define D_PTR_H#include <QObject>template <typename T>static inline T *GetPtrHelper(T *ptr) { return ptr; }#define DECLARE_PRIVATE(Class) \    inline Class##Private* d_func() { return reinterpret_cast<Class##Private*>(GetPtrHelper(d_ptr)); } \    inline const Class##Private* d_func() const { return reinterpret_cast<const Class##Private*>(GetPtrHelper(d_ptr)); }\    friend class Class##Private;#define DPTR(Class) Class##Private * const d  = d_func()class MyClassPrivate;class MyClass : public QObject{    Q_OBJECTpublic:    explicit MyClass(QObject *parent = 0);    virtual ~MyClass();    void testFunc();protected:    MyClass(MyClassPrivate &d);private:    DECLARE_PRIVATE(MyClass)    MyClass(const MyClass&);    MyClass& operator= (const MyClass&);    MyClassPrivate * const d_ptr;};#endif // D_PTR_H

d_ptr.cpp

include "d_ptr.h"#include "d_ptr.h"#include "q_ptr.h"MyClass::MyClass(QObject *parent) :    QObject(parent),    d_ptr(new MyClassPrivate(this)){}MyClass::~MyClass(){    DPTR(MyClass);    delete d;}void MyClass::testFunc(){    DPTR(MyClass);    d->fool();}

q_ptr.h

#ifndef Q_PTR_H#define Q_PTR_H#include <QObject>#include "d_ptr.h"#define DECLARE_PUBLIC(Class) \    inline Class* q_func() { return static_cast<Class *>(q_ptr); } \    inline const Class* q_func() const { return static_cast<const Class *>(q_ptr); } \    friend class Class;#define QPTR(Class) Class * const q = q_func()class MyClassPrivate : public QObject{    Q_OBJECTpublic:    MyClassPrivate(MyClass *q, QObject *parent = 0);    virtual ~MyClassPrivate() {}signals:    void testSgnl();private slots:    void testSlt();public:    void fool();private:    DECLARE_PUBLIC(MyClass)    MyClass * const q_ptr;};#endif // Q_PTR_H

q_ptr.cpp

#include "q_ptr.h"MyClassPrivate::MyClassPrivate(MyClass *q, QObject *parent) :    QObject(parent), q_ptr(q){    connect(this, SIGNAL(testSgnl()), this, SLOT(testSlt()));}void MyClassPrivate::fool(){    emit testSgnl();}void MyClassPrivate::testSlt(){    printf("This is a pimpl pattern sample implemented in qt's \"d_ptr, q_ptr\" way\n");}

main.cpp

#include "q_ptr.h"int main(/*int argc, char *argv[]*/){    MyClass * d_ptr = new MyClass;    d_ptr->testFunc();    delete d_ptr;//    while(1);    return 0;}