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Re: Call the AC_CHECK_HEADER macro on a condition
From: |
Thomas Petazzoni |
Subject: |
Re: Call the AC_CHECK_HEADER macro on a condition |
Date: |
Tue, 19 Apr 2016 15:40:00 +0200 |
Hello,
On Tue, 12 Apr 2016 11:05:51 -0400, Nick Bowler wrote:
> There are several basic solutions:
>
> - First, you can just expand AC_PROG_CPP directly and unconditionally
> before your if. This will ensure the macro is available in both cases.
>
> - Second is to rewrite your condition using AS_IF, which automatically
> "hoists" the dependency AC_PROG_CPP (and any other dependencies)
> outside of the if condition. For example:
>
> AS_IF([test x"$host" = x"avr"],
> [AC_CHECK_HEADER([avr/io.h], [],
> [AC_MSG_ERROR([missing header: avr/io.h])])
> AC_CHECK_HEADER([util/delay.h], [],
> [AC_MSG_ERROR([missing header: util/delay.h])])],
>
> [AC_CHECK_HEADER([stdio.h], [],
> [AC_MSG_ERROR([missing header: stdio.h])])
> AC_CHECK_HEADER([time.h], [],
> [AC_MSG_ERROR([missing header: time.h])])])
>
> - Third, you can make the checks unconditional but the hard
> failures conditional, e.g.:
>
> AC_CHECK_HEADER([avr/io.h], [],
> [if test x"$host" = x"avr"; then
> AC_MSG_ERROR([missing header: avr/io.h])
> fi])
I just wanted to thank you for this explanation. I was not affected by
the original issue, but your answer was very useful. Until now, I
thought AS_IF() was just a stupid wrapper around the shell's if clause,
but your answer makes it clear that it is a lot smarter than that.
Thanks!
Thomas
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com