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* c++/7201: Multiple inheritance from classes without data members wastes memory
@ 2002-07-03 11:06 markus
0 siblings, 0 replies; 2+ messages in thread
From: markus @ 2002-07-03 11:06 UTC (permalink / raw)
To: gcc-gnats
>Number: 7201
>Category: c++
>Synopsis: Multiple inheritance from classes without data members wastes memory
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Wed Jul 03 11:06:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Markus L. Noga
>Release: 2.96 20000731 (Red Hat Linux 7.3 2.96-110), 2.95.3-5 (cygwin special)
>Organization:
>Environment:
2.96 20000731 (Red Hat Linux 7.3 2.96-110) and
2.95.3-5 (Windows XP Professional, cygwin special)
>Description:
Classes without data members occupy at least one byte,
even if they do not require a vtable pointer:
class X1 {};
-> sizeof(X1)==1
When inheriting from classes without data member, the mysterious bytes add up:
class X2 {};
class X3 : public X1, public X2 {};
-> sizeof(X3)==2
They even persist when finally inheriting from a class
with data members:
class X4 { int i; };
class X5 : public X3, public X4 {};
-> sizeof(X5)==8 (due to alignment)
Forcing packed structures does not change this.
>How-To-Repeat:
#include <iostream>
class X1 {};
class X2 {};
class X3 : public X1, public X2 {};
class X4 { int i; };
class X5 : public X3, public X4 {};
int main(int argc, char **argv) {
cout << sizeof(X1) << endl;
cout << sizeof(X2) << endl;
cout << sizeof(X3) << endl;
cout << sizeof(X4) << endl;
cout << sizeof(X5) << endl;
return 0;
}
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: c++/7201: Multiple inheritance from classes without data members wastes memory
@ 2002-07-03 12:30 nathan
0 siblings, 0 replies; 2+ messages in thread
From: nathan @ 2002-07-03 12:30 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, markus, nobody
Synopsis: Multiple inheritance from classes without data members wastes memory
State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Wed Jul 3 12:30:21 2002
State-Changed-Why:
fixed in the 3.0 series. Please refer to the abi
document at http://www.codesourcery.com/cxx-abi/
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7201
^ permalink raw reply [flat|nested] 2+ messages in thread
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2002-07-03 11:06 c++/7201: Multiple inheritance from classes without data members wastes memory markus
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