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Satz Klauer wrote:

int my_lua_called_c_fct(lua_State *L)

there seems to be "L" where I could get these user data from. But how
can I put the data to "L" during initialisation and how can I retrieve
them within that function?

These are some configuration-data that are required to execute


Normally you would stash the userdata in the registry table. Two options exist for this; the first is to use a string key and retrieve it with code along the lines of:
   lua_pushliteral(L, "mykey");
   lua_gettable(L, LUA_REGISTRYINDEX);
   MyType* data = "" lua_touserdata(L, -1);

Another alternative, slightly faster (because you don't have to intern the string each time) is to use a light user data pointed at a glo bal constant for the key:
   static const char* mykey = "This string is completely ignored";
   lua_pushlightuserdata(L, mykey);
   lua_gettable(L, LUA_REGISTRYINDEX);
   MyType* data = "" lua_touserdata(L, -1);

The registry table is a table that is global to the interpreter (and not normally visible to script)