How to test a C++ library usability in configure.in?

Question

I'm working on a C++ project on GNU/Linux and I'm looking for a way to test the existence and usability of IBM Informix's library with the Autotools - namely, editing a configure.in. I don't have experience with Autotools, so basically I'm picking up from the project's configure.in et al. scripts and copying&changing where I feel needs to be changed. IOW, I've been adapting from the existing text in configure.in.

So far I've been using successfully the AC_CHECK_LIB in configure.in to test whether a certain library both exists and is usable. But this only seems to work with libraries with functions, not e.g. classes. Namely, this fails when testing Informix's libifc++.so library:

AC_CHECK_LIB(ifc++, ITString, 
        INFORMIX_LIB="-L$INFORMIX_LIB_LOCATION/c++ -lifc++ -L$INFORMIX_LIB_LOCATION -L$INFORMIX_LIB_LOCATION/dmi -L$INFORMIX_LIB_LOCATION/esql -lifdmi -lifsql -lifasf -lifgen -lifos -lifgls -lifglx $INFORMIX_LIB_LOCATION/esql/checkapi.o -lm -ldl -lcrypt -lnsl",
        echo "* WARNING: libifc++.so not found!"
        INFORMIX_INC=""
        INFORMIX_LIB=""
)

I've also tried using other combinations, like ITString::ITString, etc.

I haven't found a "pure" function in Informix's API (i.e., one that isn't contexted in a C++ class). So I'm hoping that either there's a way to use AC_CHECK_LIB in this context, or there's another autoconf/configure.in "command" for this specific use.

Thanks in advance for your feedback.

Answer 1

There might be a cleaner way of achieving this, but I think your problem is that C++ methods get "mangled" to allow additional information about the method (argument & return types etc) to be encoded. For example; the method int A::foo(void) will get mangled to something like __ZN1A3fooEv.

So you need to find the mangled name of a method in the library. You can do this by using the nm command on Unix-like OSs:

$ nm libifc++.so | grep ITString

It's worth mentioning that the exact mangling format varies across different compilers; and so by embedding a certain compiler's mangled symbol in your configure.in it may not work on other platforms - YMMV.

Note: you can use the c++filt utility to demangle a name back to it's human-readable form; so for the example I gave previously:

$ c++filt __ZN1A3fooEv
A::foo()

See Name Mangling in C++ on Wikipedia for more information.