Re: Trying to be fancy with feature testing

[Eric Blake]

According to NightStrike on 3/6/2010 10:23 AM:
> It comes up often that we want to test to see whether a feature of GCC
> works.  For instance, we want to see if -m64 is a valid gcc option to
> know if we should build the 64-bit libraries by default.  Other things
> include checking for unicode support, and the -municode option.  To do
> this, we usually do something like the following:
> 
> _save_CFLAGS="$CFLAGS"

Overkill.  Shell assignments are NOT subject to word splitting, so it
_does not matter_ whether $CFLAGS contains spaces.  It is perfectly safe
to use:

_save_CFLAGS=$CFLAGS

> CFLAGS="$CFLAGS option"

This line does indeed need double quotes, but that is in order to include
literal whitespace as part of the word that will later be interpreted as a
shell assignment.  It is also possible (although less common) to write
this as:

CFLAGS=$CFLAGS\ option

with no change in semantics.

> AC_COMPILE_IFELSE([AC_LANG_PROGRAM.......
> CFLAGS="$_save_CFLAGS"
> 
> I was trying to improve upon that using AS_VAR_COPY for the
> save/restore, but I can't figure out how to handle variables
> containing spaces.

They are handled like any other variable.

AS_VAR_COPY([_save_CFLAGS], [CFLAGS])

-- 
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden

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