Question

I’m trying to create a library that I can load into Lua with require or package.loadlib, but I have so far been unsuccessful. The library itself is in C++, but as far as I can tell I’ve taken the step necessary to properly export the function to load the library. In a nutshell, this is the relevant section of my C/C++ code:

extern "C"
{

// This line is copied from http://gcc.gnu.org/wiki/Visibility
// it's actually in a header, including it here for brevity
#define EXPORT __attribute__((visibility("default")))

EXPORT int luaopen_foo(lua_State* L)
{
    luaL_register(L, "Foo", fooL_table);
    return 0;
}

}

In my Lua script, I have this:

mylib = package.loadlib("libfoo.so", "luaopen_foo")
print(mylib) -- prints "nil"

The library is being created from a Makefile generated by CMake, and in the CMakeLists.txt I have tried compiling with various options, such as

add_library(foo STATIC ${foo_SOURCES})
add_library(foo MODULE ${foo_SOURCES})
add_library(foo SHARED ${foo_SOURCES})

And none of these options appear to work.

Are there any steps I’m missing to make this work? I’m having a hard time finding information on how to do this properly online so any guidance is welcome. I’m using is Ubuntu with gcc to compile.

Answer 1

In the Lua manual, it says, “libname must be the complete file name of the C library, including if necessary a path and extension.” Is your .so file in that directory, with that name?