Default value of pointer - c++

Question

I already knew that value of pointer member of class is undefined if it is not initialized in constructor (refer this question). I made a simple example to test it.
main.cc
#include <iostream>
class Foo {
public:
Foo() {
std::cout << __FUNCTION__ << std::endl;
count = 10;
}
void test() {
std::cout << __FUNCTION__ << count << std::endl;
}
private:
int count;
};
class Bar {
public:
void bar() {
std::cout << __FUNCTION__ << std::endl;
std::cout << m_foo << std::endl;
m_foo->test();
m_foo = new Foo();
std::cout << m_foo << std::endl;
}
private:
Foo *m_foo;
};
int main(int argc, char *argv[])
{
std::cout << __FUNCTION__ << std::endl;
Bar bar;
bar.bar();
return 0;
}
If I use g++:
g++ -std=c++11 main.cc -o test
It runs with error as expected:
main
bar
0
Segmentation fault
But, if I change to compile with clang++:
clang++ -std=c++11 main.cc -o test
It runs without any error:
main
bar
0x400920
test-1991643855
Foo
0x1bf6030
As you see, although the pointer is not initialized, it has address not NULL and it can call the function test normally. How can I prevent this error with clang++?

Answer 1

There is no "default value" for pointers. m_foo is not initialized, period. So dereferencing it is undefined behaviour. Be aware that "undefined behaviour" includes "apparently working fine".
Declare m_foo like this:
Foo * m_foo = nullptr;
Dereferencing a nullptr is still undefined behaviour, but on most platforms this will trigger a segmentation fault.