Did you know that the following will generate a compiler error?
class X {
public:
X() {}
virtual ~X() {}
virtual void A() {}
void B() {}
private:
char data[4];
};
class Q {
protected:
char data[8];
};
class Y : public X, public Q {
public:
Y() {}
virtual ~Y() {}
virtual void A() { data[1] = '2'; }
void B() {}
};
The error generated is:
test.cpp: In member function `virtual void Y::A()':
test.cpp:26: error: reference to `data' is ambiguous
test.cpp:18: error: candidates are: char Q::data[8]
test.cpp:12: error: char X::data[4]
test.cpp:26: error: `data' was not declared in this scope
At least with GCC 3.4.5. I find this annoying because Y::A() technically only has access to Q::data, not to X::data. Also, did you know that adding virtual methods to a class increases its size? Note:
#include <iostream>
struct X {
public:
virtual void A() {}
void B() {}
private:
char data[4];
};
struct Y {
public:
void A() {}
void B() {}
private:
char data[4];
};
int main(int argc, char **argv) {
using namespace std;
cout << "Sizeof X: " << sizeof(X) << " sizeof Y: " << sizeof(Y);
}
gives the output:
jason@localhost ~/Programming/sizeof $ ./a.out
Sizeof X: 8 sizeof Y: 4