casts and pointers

[Wade Ward]

[repost]
[snipped from elsewhere]

You can't. Fortran doesn't do that - not even with the C interop stuff.
Of course,you can always play around with TRANSFER, but recall that the
standard says that the resulting values are undefined when you type
cheat with TRANSFER. And you can do it in C.

You can't do it portably in C, either. I believe you can memcpy() in
to an (unsigned char *) and back again. If sizeof(int) >= sizeof(void*)
you might be able to do the cast, but the use of the value of the
int is non-portable. Those writing large model x86 code, and
who try to do such casts, know all about this one.

I suppose you are trying to use a structure constructor here. You can't
do that with C_PTR as it has (intentionally) private components. The
whole point of private components is to keep you from fiddling with the
innards. You can't write a structure constructor for a private component
- you don't even know what the components are. Now maybe you know what a
C pointer better look like inside, but accordingh to the Fortran
compiler, you don't know.

From K&R2 (close, but not exactly, the C89 standard) A6.6:

"Certain other conversions involving pointers and integers are
permitted, but have implementation defined aspects. They must
be specified by an explicit type-conversion operator, or cast."

"A pointer may be converted to an integral type large enough to
hold it; the required size is implementation-dependent. The
mapping function is also implementation dependent."

"An object of integral type may be explicitly converted to a
pointer. The mapping always carries a sufficiently wide integer
converted from a pointer back to the same pointer, but is
otherwise implementation-dependent."

Can someone in the know comment on the above?