Re: Invalid pointer dereference, or not?
loose AT astron DOT nl <loose@astron.nl> wrote:
I was quite baffled to see this (simplified) program run without
segfaults, and without valgrind complaining about invalid memory
reads.
<code>
#include <iostream>
using namespace std;
class A
{
public:
A() { cout << "A()" << endl; }
~A() { cout << "~A()" << endl; }
void print() const { cout << "Hello World" << endl; }
};
int main()
{
A* a;
a->print(); // Should segfault, shouldn't it?
a = new A();
a->print();
delete a;
a->print(); // Should segfault, shouldn't it?
return 0;
}
</code>
Is this valid/correct C++? Any ideas?
No, your program has undefined behavior. Since print() does not access
the "this" pointer of your A object, it appears to work. However, if
you were to add a data member to A and try to access it in your
function, you most likely will get an error. Do not rely on this
behavior, i.e., do not use pointers that do not point to a valid object.
--
Marcus Kwok
Replace 'invalid' with 'net' to reply
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