dnl Available from the GNU Autoconf Macro Archive at:
dnl http://www.gnu.org/software/ac-archive/htmldoc/ac_cxx_explicit.html
dnl
AC_DEFUN([AC_CXX_EXPLICIT],
[AC_CACHE_CHECK(whether the compiler supports the explicit keyword,
ac_cv_cxx_explicit,
[AC_LANG_SAVE
 AC_LANG_CPLUSPLUS
 AC_TRY_COMPILE([class A{public:explicit A(double){}};],
[double c = 5.0;A x(c);return 0;],
 ac_cv_cxx_explicit=yes, ac_cv_cxx_explicit=no)
 AC_LANG_RESTORE
])
if test "$ac_cv_cxx_explicit" = yes; then
  AC_DEFINE(HAVE_EXPLICIT,,[define if the compiler supports the explicit keyword])
fi
])