Accessing main program global variables from a dlopen()ed dynamic library in C on OS X

Question

I am maintaining a small application that has some plugin-like functionality, which is implemented through runtime-loaded dynamic modules.

Specifically, since it\'s

Answer 1

Since you declare

int global;

in the multiply.h header, the DLL and main program both have their own copy of it. Instead, declare the global in main.c

int global;

and in multiply.c declare it as extern:

extern int global;

Now if you link main.cpp with the -rdynamic option, then the executable's symbols will get exported to the DLL.

I tested this under linux and it worked, but I'm afraid I dont have access to test on MacOS. Since your ssample code also didn't work on linux, I expect this was the problem.

Answer 2

Put the global in main.c and declare it extern in the shared object, and try this:

MACOSX_DEPLOYMENT_TARGET=10.3 ld -dylib -undefined dynamic_lookup -o multiply.so multiply.o

or

MACOSX_DEPLOYMENT_TARGET=10.3 libtool -dynamic -undefined dynamic_lookup -o multiply.so multiply.o

It worked for me on Mac OS X 10.4