Re: how to check for a C++ class library

[Ralf Wildenhues]

Hello Satya,

* Satya wrote on Sun, Jan 28, 2007 at 03:13:11AM CET:
> I have to autoconfiscate a package that depends on a C++ class library. How
> can I put a check in configure.ac to check for this dependency ? I looked at
> AC_CHECK_LIB() but this library is full of classes and no directly exposed
> functions.

And what's more, real C++ functions that aren't `extern "C"' are ugly to
check with AC_CHECK_LIB anyway.  You could use something like this
(untested):

  # somewhere earlier: AC_LANG([C++])
  # ...
  satya_save_LIBS=$LIBS
  LIBS="-lmy_class_lib $LIBS"
  AC_CACHE_CHECK([for my_class_lib], [satya_cv_my_class_lib],
    [AC_LINK_IFELSE([AC_LANG_PROGRAM([
         #include <lib-header>
        ], [
          some_expression_that_involves_both_header_and_library_functions
        ])
      ], [satya_cv_my_class_lib=yes], [satya_cv_my_class_lib=no])
    ])
  LIBS=$satya_save_LIBS
  if test "$satya_cv_my_class_lib" = yes; then
    # do whatever adjusting you need to do for presence of the library
    : ...
  fi

> Do I have to write my own macro ?

If you do more than one such check, it would probably be useful to wrap
the test in a macro, yes.  It could amount to something like

  # SATYA_CXX_LIB_CHECK(LIBRARY-NICE-NAME, CACHE_VAR, PROLOGUE, EXPR, LIB,
  #                     [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
  AC_DEFUN([SATYA_CXX_LIB_CHECK],
  [
    AC_LANG_ASSERT([C++])dnl
    satya_save_LIBS=$LIBS
    LIBS="$5 $LIBS"
    AC_CACHE_CHECK([for $1], [$2],
      [AC_LINK_IFELSE([AC_LANG_PROGRAM([$3], [$4])],
         [AS_VAR_SET([$2], [yes])], [AS_VAR_SET([$2], [no])])
      ])
    LIBS=$satya_save_LIBS
    AS_IF([test AS_VAR_GET([$2]) = yes], [$6], [$7])
  ])

and then call that like this:

  SATYA_CXX_LIB_CHECK([my_class_lib], [satya_cv_my_class_lib],
    [[#include <lib-header>]],
    [some_expression_that_involves_both_header_and_library_functions],
    [-lmy_class_lib], [...])

Completely untested, all typos and thinkos are mine.  ;-)
(Instead of the AC_LANG_ASSERT, you could also bound the macro by
AC_LANG_PUSH([C++]) and AC_LANG_POP([C++])).

Hope that helps.

Cheers,
Ralf