Re: [Boost-build] Python port development

Subject: Re: [Boost-build] Python port development
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-07-09 15:56:32

AMDG

Artyom wrote:
> That is exactly the way it should not be done, and that is exactly the reason 
> you
> should give it to build system:
>
> Why it can't be done using printing the sizeof: It does not work when you cross 
> compile,

Oh.  Right.

> How can we check for example if sizeof(wchar_t) >= 4?
>   

There are many ways to trigger a compiler error in C++.
In C, yeah, a negative array size is probably the easiest.

>    char test[sizeof(wchar_t)*2 - 7]
>
> If sizeof(wchar_t) == 4 then 4*2-7 == 1 and the code is legal and compilation 
> succeeds,
> If sizeof(wchar_t) ==  2 then 2*2 - 7 == -3 and this code is not legal and 
> compilation fails.
>
> It is very tricky to implement this correctly.

How is this particularly tricky?  I can see that it would get tedious
is the size is not known to be one of a few possibility (thus requiring
a binary search), but it seems like this is rather the obvious solution
when running a compiled program isn't possible.

> This is why it shouldn't be done 
> by users
> as most of them would use the solution you had suggested, and it is wrong.
>
> Just to make it clear, even CMake had done this right only recently, before this 
> it was implemented
> incorrectly. This solution was discovered very long time ago by autotools.
>   

In Christ,
Steven Watanabe