strict aliasing

[Patrick Horgan]

Ingo Rohloff wrote:
> ...skillful elision by patrick who is rarely caught top posting;)...
> Is the above statement OK or not ?
>   
Yep
> Or is it, because "ptr2" is an "unsigned char *", that ptr2 is assumed to
> be able to alias anything ? (Because it is a char pointer).
>   
Yep
> Does these "char pointer can alias anything" really only refer to "char *"
> or also to "unsigned char *".
>   
Any char type--see below.

C++ spec says (along with a footnote that says: 49) The intent of this 
list is to specify those circumstances in which an object may or may not 
be aliased.)

15 If a program attempts to access the stored value of an object through 
an lvalue of other than one of the following types the behavior is undefined
— the dynamic type of the object,
— a cv-qualified version of the dynamic type of the object,
— a type similar (as defined in 4.4) to the dynamic type of the object,
— a type that is the signed or unsigned type corresponding to the 
dynamic type of the object,
— a type that is the signed or unsigned type corresponding to a 
cv-qualified version of the dynamic type of the object,
— an aggregate or union type that includes one of the aforementioned 
types among its members (including, recursively, a member of a 
subaggregate or contained union),
— a type that is a (possibly cv-qualified) base class type of the 
dynamic type of the object,
— a char or unsigned char type.


so accessing as a char * is ok. They did this for backward compatibility 
with bazillions of programs which do this.

Patrick