help about inheritance and this pointer

[neoreturned]

hi everyone i hav a porgram and it is uses streams and files also inheritances....

//////////////////////
.
.
.

class base{
protected:
int a;
int b;
public:
void getdata()
{}

void FileWrite(const char* filename,int no)
{
ofstream dos(filename,ios::binary|ios::app);
dos.seekp(no*sizeof(*this));
dos.write((char*)this,sizeof(*this));
}
};
.
.
.
class derivedublic base
{
private:
int c;
public:
void FileWrite(const char* filename,int no)
{
base::FileWrite(filename,no);
}
};
.
.
.
int main()
{
derived* derobj=new derobj;

derobj->getdata();
derobj->FileWrite("FILE.DAT",0);
}


In this program derived's class FileWrite function sees this pointer as derived object and sizeof(*this)=12...(sizeof(int)=4). But base::FileWrite() function sees this derived object but sizeof(*this)=8...
and it only see base datas not derived(in this int c is derived's data...)

What is wrong and how can i fix this problem????

 

[cpjust]

There is no problem. That's how it's supposed to work. base has 2 ints (2 x 4 bytes), and derived has 3 ints (3 x 4 bytes). base can never see data in derived classes; what would be the point?

 

[neoreturned]

void FileWrite(const char* filename,int no)
{
base::FileWrite(filename,no);
}
derobj call derived class's FileWrite() so 'this' is derobj's address

in this program when we enter base::FileWrite(filename,no);
line this shows derobj->a,derobj->b but not derobj->c it is the porblem why NOT derobh->c