Re: conversion from array to reference to pointer

"kanze" <>
Fri, 9 Jun 2006 11:03:46 CST
<> wrote:

Hi everybody do you think this little chunk of code is legal and leads
to defined results?

int main()
   char v[] = "";
   char *const& p = reinterpret_cast<char*const&>(v);

Legal. v is an lvalue with type char[1]. The standard says
that you can use reinterpret_cast to convert any lvalue to a reference
of any other type (practically). Of course, since v isn't a pointer, p
(which refers to it) can't be accessed.

   return *p;

And this is undefined behavior. Logically, you've taken the address of
v, and told the compiler that the data at that address is a pointer.
Which you then dereference. You can't just take any random memory
address, tell the compiler its a pointer, and then deference it.


And the next one?

int main()
   char v[] = "";
   char *& p = reinterpret_cast<char*&>(v);
   return *p;

No difference.

Note that these examples are syntactically legal only because the
compiler has no reason to apply the array-to-pointer conversion. I
would not be surprised if some compilers applied it anyway, and said
that the code was illegal, because you are trying to convert a
non-lvalue to a reference (which isn't allowed in a reinterpret_cast).

James Kanze GABI Software
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