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16.4.3 Libtool C++ support

At the moment, Libtool is the weak link in the chain when it comes to working with C++. It is very easy to naively build a shared library from C++ source using libtool:

$ libtool -mode=link g++ -o -rpath /usr/local/lib foo.c++

This works admirably for trivial examples, but with real code, there are several things that can go wrong:

  • On many architectures, for a variety of reasons, libtool needs to perform object linking using ld. Unfortunately, the C++ compiler often links in standard libraries at this stage, and using ld causes them to be dropped.

    This can be worked around (at the expense of portability) by explicitly adding these missing libraries to the link line in your `Makefile'. You could even write an Autoconf macro to probe the host machine to discover likely candidates.

  • The C++ compiler likes to instantiate static constructors in the library objects, which C++ programmers often rely on. Linking with ld will cause this to fail.

    The only reliable way to work around this currently is to not write C++ that relies on static constructors in libraries. You might be lucky enough to be able to link with LD=$CXX in your environment with some projects, but it would be prone to stop working as your project develops.

  • Libtool's inter-library dependency analysis can fail when it can't find the special runtime library dependencies added to a shared library by the C++ compiler at link time.

    The best way around this problem is to explicitly add these dependencies to libtool's link line:

    $ libtool -mode=link g++ -o -rpath /usr/local/lib foo.cxx \
    -lstdc++ -lg++

Now that C++ compilers on Unix are beginning to see widespread acceptance and are converging on the ISO standard, it is becoming unacceptable for Libtool to impose such limits. There is work afoot to provide generalized multi-language and multi-compiler support into Libtool----currently slated to arrive in Libtool 1.5. Much of the work for supporting C++ is already finished at the time of writing, pending beta testing and packaging(36).

This document was generated by Gary V. Vaughan on February, 8 2006 using texi2html