Question

This is probably an easy question, but I am stumped. This is for Lua 5.1.

I have a script which runs in its own environment. In that environment, I have a variable called “plugin” I set from C++ like so:

    lua_getfield(L, LUA_REGISTRYINDEX, getScriptId());  // Put script's env table onto the stack  -- env_table

    lua_pushstring(L, "plugin");  //                           -- env_table, "plugin"
    luaW_push(L, this);       //                               -- env_table, "plugin", *this
    lua_rawset(L, -3);        // env_table["plugin"] = *this   -- env_table

    lua_pop(L, -1);           // Cleanup                       -- <<empty stack>>

Before running my Lua script, I set the function environment like so:

 lua_getfield(L, LUA_REGISTRYINDEX, getScriptId());    // Push REGISTRY[scriptId] onto stack           -- function, table
 lua_setfenv(L, -2);                                   // Set that table to be the env for function    -- function

When my script runs, it can see and interact with the plugin variable, as expected. So far, so good.

At one point, the Lua script calls a C++ function, and in that function, I want to see if the plugin variable is set.

I have tried many many things, and I can’t seem to see the plugin variable. Here are but 4 things I tried:

lua_getfield(L, LUA_ENVIRONINDEX, "plugin");
bool isPlugin = !lua_isnil(L, -1);
lua_pop(L, 1);    // Remove the value we just added from the stack

lua_getfield(L, LUA_GLOBALSINDEX, "plugin");
bool isPlugin2 = !lua_isnil(L, -1);
lua_pop(L, 1);    // Remove the value we just added from the stack

lua_getglobal(L, "plugin");
bool isPlugin3 = !lua_isnil(L, -1);
lua_pop(L, 1);    // Remove the value we just added from the stack

lua_pushstring(L, "plugin");
bool isPlugin4 = lua_isuserdata(L, -1);
lua_pop(L, 1);

Unfortunately, all the isPlugin variables return false. It is as if the C++ function called from Lua cannot see a variable set in a Lua environment.

Any idea how I can see the plugin variable from C++?

Thanks!

Answer 1

Every function in Lua has it’s own environment. They don’t inherit the environment of whomever calls them. So if your C++ function doesn’t use the environment that has this plugin variable, then it won’t see it.