[prog] GNU autotools and namespaced libraries

[John Clarke]

On Wed, Dec 15, 2004 at 09:32:00 -0600, Meredith L. Patterson wrote:

> unpacking what you mean by "functions which have a C linkage", though;
> would you mind elaborating?

Anything enclosed in 'extern "C" { ... }' has a C linkage, i.e. it's
pure C code.  The compiler doesn't do the C++ name mangling on anything
in these blocks, the same as if that part of the code was compiled with
a C compiler. 

Here's an example:

    [johnc at dropbear ~/tmp]$ cat test.C
    char func1()
    {
        return 'a';
    }
    
    extern "C"
    {
        char func2()
        {
            return 'a';
        }
    }
    [johnc at dropbear ~/tmp]$ gcc -c test.C
    [johnc at dropbear ~/tmp]$ nm test.o | grep func
    00000000 T func1__Fv
    00000008 T func2

See what the compiler has done to func1's name in the object file? 
That's name mangling, and it's why AC_CHECK_LIB fails.  func2 though,
being C, is unchanged, and AC_CHECK_LIB will be able to find it.


Does this help?


Cheers,

John
-- 
I also had to use Visual Source Safe at one job, but that was a trauma I
hope  never to repeat.  It would have been better for source code
control to post  our source code to comp.sources.unix and retrieve the
versions using  groups.google.com.                  -- Paul Tomblin