From: eldiener@tropicsoft.invalid   
      
   On 7/19/2013 8:02 PM, kawninzx6@googlemail.com wrote:   
   > Hi C++ experts,   
   >   
   > Is it ever safe to dereference a NULL pointer?  Specifically,   
   > I'm curious about dereferencing NULL during dynamic_cast.   
   >   
   > Contrived example code:   
   > // includes omitted   
   >   
   > class BaseFoo   
   > {   
   >    public:   
   >      virtual ~BaseFoo() {}   
   > };   
   >   
   > class Foo : public BaseFoo {};   
   >   
   > void process(int& i) { ... }   
   >   
   > void process(Foo& foo) { ... }   
   >   
   > BaseFoo* getFoo() { ... }   
      
   I assume you meant:   
      
   BaseFoo* getFoo() { return 0; }   
      
   >   
   > int main()   
   > {   
   >    int *i = NULL;   
   >    void process(*i); // (1)   
      
   That's not safe. You will probably get an OS exception at run-time for   
   trying to read memory at 0.   
      
   >   
   >    try   
   >    {   
   >      process(dynamic_cast(*getFoo())); // (2)   
      
   That's not safe also. Ditto with the above.   
      
   >    }   
   >    catch (const std::exception&)   
   >    {   
   >      // ignore bad_cast exception   
   >    }   
   >   
   >    return 0;   
   > }   
   >   
   > (1) - This is always undefined behavior, right?   
   > (2) - Does this dynamic_cast produce undefined behavior if   
   >        getFoo() returns a NULL pointer?   
   >   
   > If it matters, I'm not using C++11.   
      
   Neither are safe and both invoke undefined behavior. C++ doesn't tell   
   the OS what to do but an operating system exception for accessing memory   
   at 0 normally occurs in my experience.   
      
      
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