A very unpleasant scenario possible when you forget to initialize a pointer to a class. Let's say, we have class CBase with a member function which doesn't use member data, i.e. it doesn't need
this pointer.
class CBase
{
int i;
public:
void f() { std::cout<<"CBase::f"<<std::endl;}
};
And after that you write the following code somewhere:
CBase* p = NULL;
p->f();
This is an undefined behavior by the Standard. But sometimes it works. Visual Studio 2008, for example, generates a working code. The function call is resolved during the compilation, we don't use
this. And you remain oblivious for a long period of time. Here is a scarier looking example
((CBase*)0)->f();
But when you try to use
this pointer, you program "crashes". Examples:
class CBase
{
int i;
public:
virtual void f() { std::cout<<"CBase::f"<<std::endl;}
};
class CBase
{
int i;
public:
void f() { std::cout<<"CBase::f"<<std::endl; i=0;}
};
All this leads to very interesting, hard to find bugs.
Links:
comp.lang.c++.moderated - Functions that don't use this, called with uninitialized pointers
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