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digitalmars.D.bugs - [Issue 9021] New: Casting a class pointer to size_t and back does not return the same value

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9021

           Summary: Casting a class pointer to size_t and back does not
                    return the same value
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: malteskarupke web.de


--- Comment #0 from Malte Skarupke <malteskarupke web.de> 2012-11-13 17:44:49
PST ---
int main()
{
    class C { }
    C c = new C;
    C other = *cast(C *)cast(size_t) &c;
    assert(&other == &c);
    return 0;
}

That assert fires on DMD 2.060

I need this to interface with a C library where I have to pass a pointer as two
ints and then cast them back in a callback.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9021


Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com


--- Comment #1 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-11-13
17:47:13 PST ---
(In reply to comment #0)

 int main()
 {
     class C { }
     C c = new C;
     C other = *cast(C *)cast(size_t) &c;
     assert(&other == &c);
     return 0;
 }
 
 That assert fires on DMD 2.060
 
 I need this to interface with a C library where I have to pass a pointer as two
 ints and then cast them back in a callback.


You are comparing references. Those are two unique references to the same
object. If you want to compare the actual object address they point to use:

cast(void*)other == cast(void*)c;

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prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9021


Malte Skarupke <malteskarupke web.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


--- Comment #2 from Malte Skarupke <malteskarupke web.de> 2012-11-13 18:01:02
PST ---
(In reply to comment #1)

 (In reply to comment #0)

 int main()
 {
     class C { }
     C c = new C;
     C other = *cast(C *)cast(size_t) &c;
     assert(&other == &c);
     return 0;
 }
 
 That assert fires on DMD 2.060
 
 I need this to interface with a C library where I have to pass a pointer as two
 ints and then cast them back in a callback.


 
 You are comparing references. Those are two unique references to the same
 object. If you want to compare the actual object address they point to use:
 
 cast(void*)other == cast(void*)c;


Ah that explains it. Thanks!

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