🚀 go-pugleaf

In article kav@bmtlh10.bnr.ca, John Hickin <hickin@bnr.ca> writes:
>I accidently discovered that the following code compiles and executes using my
>favourite compiler:
>
>#include <iostream.h>
>#include <stddef.h>
>
>void* operator new(unsigned sz,const char*,int)
>{
>  return ::operator new(sz);
>}
>
>struct Foo { Foo(); ~Foo(); };
>
>Foo::Foo()  { cerr << "Foo::Foo[this==" << (void*)this << ']' << endl; }
>Foo::~Foo() { cerr << "Foo::~Foo[this==" << (void*)this << ']' << endl; }
>
>main()
>{
>  Foo* p = new(__FILE__,__LINE__) Foo[ 42 ];
>  delete[] p;
>}
>
>(1) Is it legal C++?
>(2) If so, what should the behavior be?

The results of using "delete" on a pointer value obtained from a placement-
new are undefined. Any result is allowed. It is invalid C++, but no
diagnostic is required.
---
Steve Clamage, stephen.clamage@eng.sun.com

In <3vu2gv$kav@bmtlh10.bnr.ca> John Hickin <hickin@bnr.ca> writes: 
>
>I accidently discovered that the following code compiles and executes
using my
>favourite compiler:
>
>#include <iostream.h>
>#include <stddef.h>
>
>void* operator new(unsigned sz,const char*,int)
>{
>  return ::operator new(sz);
>}
>
>struct Foo { Foo(); ~Foo(); };
>
>Foo::Foo()  { cerr << "Foo::Foo[this==" << (void*)this << ']' << endl;
}
>Foo::~Foo() { cerr << "Foo::~Foo[this==" << (void*)this << ']' <<
endl; }
>
>main()
>{
>  Foo* p = new(__FILE__,__LINE__) Foo[ 42 ];
>  delete[] p;
>}
>
>
>
>(1) Is it legal C++?
>(2) If so, what should the behavior be?
>
>In my environment (HP-UX 9.x, C++ A.03.05) the Foo::Foo's are called
but the
>Foo::~Foo's are not called.  If i change new(__FILE__,__LINE__) to
just new the
>destructors get called as expected.
>
>-- 
>John Hickin      Bell-Northern Research, Montreal, Quebec
>(514) 765-7924   hickin@bnr.ca
>

Yes it is a legal C++ code. And it is supposed to call the overloaded
new one time and the ctor and dtor of the Foo for 42 times. In my
environment (Microsoft Visual C++ 2.0) the same code is working without
any change.

- Ramesh S
rameshs@ix.netcom.com

Steve Clamage (clamage@Eng.Sun.COM) wrote:

|> The results of using "delete" on a pointer value obtained from a placement-
|> new are undefined. Any result is allowed. It is invalid C++, but no
|> diagnostic is required.

Can this be true?  I always thought that the results of using delete
were to call the destructors, and then call operator delete().  If the
memory was not obtained by calling operator new( size_t ), then the
results are undefined, but in the example given, the memory was obtained
by the placement new calling operator new( size_t ).

Does this mean that I cannot delete memory obtained by:

	p = new ( nothrow() ) T ;

This would sort of make this version of new useless.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
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