类的成员函数作为回调函数

思路是借助类的静态成员函数

方式一：

class A{
public:
    A(int a){
        m_a = a;
    }
    void print(){
        cout << "m_a = " << m_a << endl;
    }
    void setCur(){
        s_curA = this;
    }
    
    static void callback(){
        s_curA->print();
    }
private:
    static A* s_curA;
    int m_a;
};
A* A::s_curA = nullptr;

typedef void (*FUN_S)();
void Handle(FUN_S call){
    call();
}

int main( )
{  
    A a(10), b(20);
    a.setCur();
    Handle(A::callback);
    b.setCur();
    Handle(A::callback);
    
    return 0;
}

方式二：

class A{
public:
    A(int a){
        m_a = a;
    }
    void print(){
        cout << "m_a = " << m_a << endl;
    }   
    static void callback(void *a){
        ((A*)a)->print();
    }
private:
    int m_a;
};

typedef void (*FUN)(void *);
void Handle(void *a, FUN call){
    call(a);
}

int main( )
{  
    A a(10), b(20);
    Handle(&a, A::callback);
    Handle(&b, A::callback);
    
    return 0;
}

输出：

Start
m_a = 10
m_a = 20
0
Finish

还可以进一步封装：

typedef void (*FUN_S)();
void Handle(FUN_S call){
    cout << "Handle(FUN_S) begin..." << endl;
    call();
    cout << "Handle(FUN_S) end..." << endl;
}
typedef void (*FUN)(void *);
void Handle(void *a, FUN call){
    cout << "Handle(void *, FUN) begin..." << endl;
    call(a);
    cout << "Handle(void *, FUN) end..." << endl;
}
class A{
public:
    A(int a){
        m_a = a;
    }
    void print(){
        cout << "m_a = " << m_a << endl;
    }
    void setCur(){
        s_curA = this;
    }
    void startup(){
        setCur();
        Handle(A::callback);
    }
    void startup(int){
        Handle(this, A::callback);
    }
    static void callback(){
        s_curA->print();
    }
    static void callback(void *a){
        ((A*)a)->print();
    }
private:
    static A* s_curA;
    int m_a;
};
A* A::s_curA = nullptr;

int main( )
{  
    A a(10), b(20);
    a.startup();
    b.startup();
    cout << "======================================" << endl;
    a.startup(1);  
    b.startup(1);  
    return 0;
}

输出：

Start
Handle(FUN_S) begin...
m_a = 10
Handle(FUN_S) end...
Handle(FUN_S) begin...
m_a = 20
Handle(FUN_S) end...
======================================
Handle(void *, FUN) begin...
m_a = 10
Handle(void *, FUN) end...
Handle(void *, FUN) begin...
m_a = 20
Handle(void *, FUN) end...
0
Finish