From: Thomas Immich <immich@ergosign.de>
To: gcc@gcc.gnu.org
Subject: Getting the byte offset of a member variable pointer type
Date: Wed, 22 Jun 2005 13:48:00 -0000 [thread overview]
Message-ID: <311FCBFD-7462-42C9-8701-5869B3AC37BE@ergosign.de> (raw)
Hi all,
I need to get the exact byte offset of a member variable inside a
class in order to map a member variable pointer type to a concrete
member variable instance. This worked fine until I ported my code to
GCC 4.0, which is much stricter regarding type casts.
Unfortunately I cannot use the offsetof() macro, since I do not have
enough information to do so.
The only information I have is:
- The member variable type (in template parameter T, for example
int)
- A member variable pointer (m_memberVariablePtr, for example
int MyClass::*)
- The class type (in template parameter C, for example MyClass)
- A concrete instance of type C (obj)
I want to get
- The address of obj's concrete member variable (represented by
m_memberVariablePtr)
Here is how I calculated this address in GCC 3.0:
const C* addressOfObject = static_cast<const C*>(&obj);
T* result = (T*)((std::size_t)addressOfObject + (size_t)
m_memberVariablePtr);
However, this snippet does not compile in GCC 4.0, since I am not
allowed to cast a member variable pointer to a size_t type. Is there
any elegant possibility to get the address correctly?
Thanks in advance,
Thomas
next reply other threads:[~2005-06-22 13:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-06-22 13:48 Thomas Immich [this message]
2005-06-22 15:55 ` Dave Korn
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