virtual2.cpp

#include <iostream>
#include <string>

class Sample1 {
public:
    virtual void vMethod1() {
        printf("This is virtual method 1\n");
        printf("member1 = %d\n", member1);
    }
    virtual void vMethod2() {
        printf("This is virtual method 2\n");    
    }
    void method2() {
        printf("This is NONVIRTUAL method 2\n");    
    }
public:
    int     member1;
    int     member2;
};

//Define method type
//Thêm tham số thisPtr ở đây
typedef void (*MyFunc)(Sample1 *thisPtr);

struct ClassDesc {
    MyFunc* vmt;
    int     member1;
    int     member2;
};

void fakeVMethod1(ClassDesc* thisPtr) {
    printf("fake virtual method1 - member1: %d\n", thisPtr->member1);
    
}

void fakeVMethod2(ClassDesc* thisPtr) {
    printf("fake virtual method2 - member2: %d\n", thisPtr->member2);
    
}

void constructor(ClassDesc* desc) {
    //Init virtual method table
    desc->vmt = new MyFunc[2];
    desc->vmt[0] = (MyFunc)&fakeVMethod1;
    desc->vmt[1] = (MyFunc)&fakeVMethod2;
}

void destructor(ClassDesc* desc) {
    //delete virtual method table
    delete []desc->vmt;
}


void override_fakeVMethod1(ClassDesc* thisPtr) {
    printf("override fake virtual method1 - member1: %d\n", thisPtr->member1);
    
}

void constructor_Extend(ClassDesc* desc) {
    constructor(desc);
    desc->vmt[0] = (MyFunc)&override_fakeVMethod1;
}

int main(int argc, const char * argv[]) {
    Sample1 *a = new Sample1();
    
    a->member1 = 1000;
    printf("size of Sample1: %d\n", sizeof(Sample1));
    
    MyFunc *virtualMethodTable = (MyFunc*)(*(MyFunc*)a);    
    
    virtualMethodTable[0](a); //call method1
    virtualMethodTable[1](a); //call method2
    
    printf("\n--------------FAKE CLASS----------------\n\n");
    
    
    ClassDesc* clsDesc = new ClassDesc(); //   |
    constructor(clsDesc);                 //   | <=>  a = new Sample1();
    
    clsDesc->member1 = 2000;
    clsDesc->member2 = 3000;
    
    Sample1* b = reinterpret_cast<Sample1*>(clsDesc); // cast Class Description struct to Sample1*
        
    b->vMethod1();
    b->vMethod2();
        
    destructor(clsDesc);        //
    delete clsDesc;             //  <=> delete b;
    
    
    printf("\n--------------FAKE INHERITANCE CLASS----------------\n\n");
    
    ClassDesc* clsDesc2 = new ClassDesc(); //   |
    constructor_Extend(clsDesc2);                 //   | <=>  a = new Sample1();
    
    clsDesc2->member1 = 2000;
    clsDesc2->member2 = 3000;
    
    b = reinterpret_cast<Sample1*>(clsDesc2); // cast Class Description struct to Sample1*
        
    b->vMethod1();
    b->vMethod2();
        
    destructor(clsDesc2);        //
    delete clsDesc2;             //  <=> delete b;
    
    return 0;
}