How can I create a pointer to existing data using the LuaJIT FFI?

Question

I know there are examples of creating pointers using the LuaJIT FFI, but most of these aren\'t pointed to existing data. One such example of this is here: How to pass a poin

Answer 1

I was able to do that with a C function that copies the cdata pointer like this

void cdataToPointer(void *cdata, void **pointer) {
    *pointer = cdata;
}

// ...

void *mycdata = NULL;

lua_pushlightuserdata(L, &mycdata);
lua_setglobal(L, "__TEMP_USERDATA__");

luaL_dostring(L,
     "local ffi = require'ffi'\n"
     "ffi.cdef[[\n"
     "  void cdataToPointer(void *cdata, void **pointer);\n"
     "]]\n"
     "ffi.C.cdataToPointer(mycdata, __TEMP_USERDATA__)\n");