Re: How to pass AC_ARG_ENABLE an argument

[Eric Sunshine]

Dave Kirkby wrote:
> What am I doing wrong here then?
> AC_ARG_ENABLE([cpus],
>    AC_HELP_STRING([--enable-CPUs=<N>], [use N CPUs in SMP mode
>        (default is 4)]),
>    AC_DEFINE([CPUS],$enable_cpus,[Enabled N CPUs in SMP mode]),
>    AC_DEFINE([CPUS],4,[Enabled the default number of CPUs in SMP mode]))
> configure --enable-cpus=12
> Then my config.h shows:
> #define CPUS $enable_cpus

Some notes:

(1) Use AC_DEFINE_UNQUOTED to get $enable_cpus to expand properly.

(2) You should handle the case when the user specifies --disable-cpus 
(or --enable-cpus=no).

(3) To avoid confusing users, your help message should reflect the 
actual option name (that is, --enable-cpus rather than --enable-CPUs).

(4) As a general rule, it is important to quote all arguments to all 
functions.  For instance, you are using AC_HELP_STRING() and AC_DEFINE() 
as arguments to AC_ARG_ENABLE(), so those invocations should be quoted. 
 For example: AC_ARG_ENABLE([cpus], [AC_HELP_STRING([--blah]...)], 
[AC_DEFINE([FOO]...)]).

Here is one possible implementation which will provide the output you 
desire, and which addresses the above issues.

AC_ARG_ENABLE([cpus],
    [AC_HELP_STRING([--enable-cpus=<N>],
        [use N CPUs in SMP mode (default is 4)])],
    [], [enable_cpus=4])
AS_IF([test $enable_cpus = no], [enable_cpus=1])
AC_DEFINE_UNQUOTED([CPUS],[$enable_cpus],[Enabled N CPUs in SMP mode])

-- ES