[gambit-list] Difficulties linking against a C++ library

John Thompson bargarply at yahoo.com
Tue Feb 24 08:41:24 EST 2009


Hi,

I'm trying to get a toy, loadable C++ library compiled.  My setup is as follows:

foo.scm:

 (define bar (c-lambda (char-string) int "cpp_bar"))

foo.cpp:

int cpp_bar(char* text) {
  return 0;
}

foo.h:

int cpp_bar(char* text);

I'm using the latest tarball of gambit, compiled with --enable-cplusplus.

I compile foo.scm to C++ via:

gsc -link -flat foo.scm ==> foo.c and foo_.c

Then I want to compile these into object files and I run into trouble.   g++ -fPIC -c foo.c outputs the following:

oo.c: In function ‘int ___H__20_foo_23_0(___processor_state_struct*)’:
foo.c:119: error: ‘cpp_bar’ was not declared in this scope
foo.c: At global scope:
foo.c:156: warning: deprecated conversion from string constant to ‘char*’

Whereas

gcc compiles it fine.  It must be a name-mangling issue, but it seems
peculiar to me, given that I compiled gsc using g++.  Moreover, I can
compile if I add extern "C" {int cpp_bar(char*);} to foo.c.  I picked
this up from reading about someone who had similar problems a few years
ago:

http://osdir.com/ml/lisp.scheme.gambit/2005-02/msg00037.html

I then compile and link like:

g++ -fPIC -c -D___DYNAMIC foo_.c foo.c
g++ -fPIC -c -D___DYNAMIC foo.cpp -o cppfoo.o
ld -G -o foo.o1 /usr/lib/libstdc++.so.6.0.9 /usr/lib/gcc/i486-linux-gnu/4.2/crtbegin.o cppfoo.o foo_.o foo.o

Unfortunately, this leads me here:

*** WARNING -- Could not find C function: "____20_foo_2e_o1"
*** ERROR IN ##main -- .../foo.o1: undefined symbol: cpp_bar
(load "foo.o1")

Can anyone offer me any pointers on how to proceed?

-John


      
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