[C++] __alignof() fails to properly evalute alignment of dependent types

[C++] __alignof() fails to properly evalute alignment of dependent types by CodingCat

Closed

as Fixed

Type:	Bug
ID:	682695
Opened:	8/2/2011 11:15:28 AM
Access Restriction:	Public
Moderator Decision:	Sent to Engineering Team for consideration

Workaround(s)

view

User(s) can reproduce this bug

The VC++ 2010 compiler fails to properly evaluate the alignment of dependent types in template argument lists when these types have not been 'in use' before being passed to __alignof().

Always evaluating sizeof() with the types in question right before evaluating __alignof() works around this issue, yet, with the introduction of alignof to C++0x, this issue might become more relevant in the future.

Details (expand)

Visual Studio 2010 SP1

#include <iostream>

template <class T>
struct foo
{
    T value;
};

template <class T, size_t A = __alignof(foo<T>)>
struct foo_alignment
{
    static const size_t value = A;
};

struct fwd_decl;

int main()
{
    // SIDE NOTE: Adding this sizeof evaluation before using foo_alignment works around the issue
//    sizeof(foo<int>);

    // ERROR: prints 0, should be 4
    std::cout << foo_alignment<int>::value << std::endl;

    // SIDE NOTE: prints 0, but should rather fail just like sizeof(fwd_decl) would?
    std::cout << __alignof(fwd_decl) << std::endl;

    return 0;
}

English

Windows Vista

German

foo_alignment<int>::value evaluates to 0

foo_alignment<int>::value should be 4

0 attachments

Posted by Microsoft on 9/6/2011 at 12:39 PM

Hi: this issue has been fixed. The fix should show up in a future release of Visual C++.

Thank you for reporting the issue.

Jonathan Caves
Visual C++ Compiler Team

Posted by MS-Moderator08 [Feedback Moderator] on 8/2/2011 at 7:38 PM

Thank you for submitting feedback on Visual Studio 2010 and .NET Framework. Your issue has been routed to the appropriate VS development team for investigation. We will contact you if we require any additional information.

Posted by MS-Moderator01 on 8/2/2011 at 11:50 AM

Thank you for your feedback, we are currently reviewing the issue you have submitted. If this issue is urgent, please contact support directly(http://support.microsoft.com)