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Re: AC_CHECK_SIZEOF for members

From: Paul Eggert
Subject: Re: AC_CHECK_SIZEOF for members
Date: Wed, 11 May 2005 11:05:53 -0700
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux)

Sam Steingold <address@hidden> writes:

>> Yes, that's correct.  You'd need to write a variant to do what you want.
> <screaming in pain>

It's not that bad, if you can assume Autoconf 2.59.  Just copy the
existing code from the sizeof-using macro, and repair it to allow
objects rather than types.

> the reason I want a CPP macro and not a run-time if is that the code
> will end up looking like this:
>   if (size_of(u.ut_tv.tv_sec) = 4)
>     a_function_expecting_32_bit_argument(u.ut_tv.tv_sec);
>   else
>     a_function_expecting_64_bit_argument(u.ut_tv.tv_sec);
> the result is that on _each_ platform there will be a compile-time
> warning about a wrong argument type.

My suggestion is to fix the compiler, or get a better compiler, or
ignore the warnings.  Your life is too short to waste it worrying
about incorrect compiler warnings.

Also, unless there is a serious efficiency issue (not likely here) or
some other issue I don't quite follow, I'd write the code like this:

  a_function_expecting_64_bit_argument (u.ut_tv.tv_sec);

This will work fine on C89 and better, if you've prototyped the function.

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