Re: [eigen] strange sizeof on windows

["Benoit Jacob" <jacob.benoit.1@xxxxxxxxx>]

Committed. Can somebody who has MSVC please svn up and retry
sizeof(Matrix<float,1,1>) and if possible the test_sizeof?

Thanks in advance,
Benoit

2009/1/5 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
> aha, great.
> Then I know what to do: remove the ei_matrix_with_aligned_operator_new
> base class of Matrix, and instead copy and paste the operators there.
>
> It'd be a bit stupid to do this just for one compiler but here really
> we've been relying on nonstandard behavior (the EBCO) from something
> crucial (that sizeof of our matrices is optimal).
>
> Cheers,
> Benoit
>
> 2009/1/5 FMDSPAM <fmdspam@xxxxxxxxx>:
>> Benoit Jacob schrieb:
>>>
>>> 2009/1/5 FMDSPAM <fmdspam@xxxxxxxxx>:
>>>
>>>>>
>>>>> can you try this:
>>>>>
>>>>> struct empty {};
>>>>> struct foo : empty
>>>>> {
>>>>>  float x;
>>>>> };
>>>>>
>>>>> and print sizeof(foo), sizeof(empty), sizeof(float) ?
>>>>>
>>>>>
>>>>
>>>> Sure,
>>>>
>>>> sizeof(foo) = 4
>>>> sizeof(empty) = 1
>>>> sizeof(float) = 4
>>>>
>>>
>>> Thanks very much. So at least here, your compiler has performed the
>>> EBCO (empty base class optimization)
>>> http://www.informit.com/articles/article.aspx?p=31473&seqNum=2
>>> (Indeed that turns out to be a nonstandard optimization performed only
>>> by certain compilers).
>>>
>>> The question now is, why doesn't it perform the EBCO with Eigen::Matrix ?
>>> Maybe it's related to the multiple inheritance. Can you please try:
>>>
>>> struct empty1 {};
>>> struct empty2 {};
>>> struct foo : empty1, empty2
>>> {
>>>  float x;
>>> };
>>>
>>> what is sizeof(foo) now ?
>>>
>>>
>>
>> Sure,
>>
>> sizeof(foo) = 8
>> sizeof(empty1) = 1
>> sizeof(empty2) = 1
>> sizeof(float) = 4
>>
>> Gotcha! :-(
>>
>>
>> ---
>>
>>
>

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