QT的d/q指针

结论：

• d指针指向private类
  • 在public接口类的成员函数中被使用
• q指针指向public类
  • 在private实现类的成员函数中被使用

FooClass.h

#include"FooClassPrivate.h"

template <typename T> static inline T *qGetPtrHelper(T *ptr) { return ptr; }

#define Q_DECLARE_PRIVATE(Class) \
    inline Class##Private* d_func() { return reinterpret_cast<Class##Private *>(qGetPtrHelper(d_ptr)); } \
    inline const Class##Private* d_func() const { return reinterpret_cast<const Class##Private *>(qGetPtrHelper(d_ptr)); } \
    friend class Class##Private;

#define Q_D(Class) Class##Private * const d = d_func()

class FooClass{
public:
    FooClass():d_ptr(new FooClassPrivate(this)){}
    virtual ~FooClass()
    {
        Q_D(FooClass);
        delete d;
    }
    int getID(){
        Q_D(FooClass);
        return d->getID();
    }
    void setID(int id){
        Q_D(FooClass);
        d->setID(id);
    }

private:
    FooClassPrivate* const d_ptr;
    Q_DECLARE_PRIVATE(FooClass)
};

FooClassPrivate.h

class FooClass;

#define Q_DECLARE_Public(Class) \
    inline Class* q_func() { return reinterpret_cast<Class *>(q_ptr); } \
    inline const Class* q_func() const { return reinterpret_cast<const Class *>(q_ptr); } \
    friend class Class;

#define Q_Q(Class) Class * const q = q_func()

class FooClassPrivate{
public:
    FooClassPrivate(FooClass* p):q_ptr(p){

    }
    int getID(){
        return _id;
    }
    void setID(int id){
        _id = id;
    }
    virtual ~FooClassPrivate(){}

private:
    FooClass* const q_ptr;
    int _id  = 0;

    Q_DECLARE_Public(FooClass)
};

main.cpp

#include <iostream>
#include "FooClass.h"

int main(){
    FooClass* foo = new FooClass();
    std::cout << "ID = "  << foo->getID() << std::endl;
    foo->setID(10);
    std::cout << "ID = "  << foo->getID() << std::endl;
    return 0;
}

运行测试

g++ -o main main.cpp
./main