Question

Apparently gnuflex on MacOS & Linux requires the -R option or %option reentrant to generate a reentrant scanner, but on FreeBSD it generates a reentrant scanner by default and throws an error if the -R or %option reentrant are provided. I’d like to have autoconf automatically check to see if gnuflex allows the -R option and, if so, provide it. It’s not clear to me how I can make autoconf test for this. My guess is that I should run gnuflex on a null file with the -R and check the result code and set some kind of variable, and then add it to the FLEX options, but I’m not really sure. Any ideas?

Answer 1

I’ll assume you’ve set $FLEX, probably with a combination of AC_ARG_VAR and AC_PATH_PROG.

AC_CACHE_CHECK([whether $FLEX supports -R],
               [my_cv_prog_flex_dash_r],
               [mv_cv_prog_flex_dash_r=no
                echo '%%' | "$FLEX" -R && my_cv_prog_flex_dash_r=yes
                rm -f lex.yy.c])
AS_IF([test $my_cv_prog_flex_dash_r = yes], [FLEX="$FLEX -R"])