Calling a lua function from table.subtable in C++

Question

im trying to call a lua function from C++ where function is in subtable of global table. Im using lua version 5.2.* compiled from source.

Lua function

function globaltable.subtable.hello()
 -- do stuff here
end

C++ code

lua_getglobal(L, "globaltable");
lua_getfield(L, -1, "subtable");
lua_getfield(L, -1, "hello");
if(!lua_isfunction(L,-1)) return;
    lua_pushnumber(L, x);
    lua_pushnumber(L, y);
    lua_call(L, 2, 0);

However im unable to call it, i always get an error

PANIC: unprotected error in call to Lua API (attempt to index a nil value)

On line #3: lua_getfield(L, -1, "hello");

What am I missing?

Side question: I would love to know also how to call function deeper than this - like globaltable.subtable.subsubtable.hello() etc.

Thank you!

This is what im using to create the globaltable:

int lib_id;
lua_createtable(L, 0, 0);
lib_id = lua_gettop(L);
luaL_newmetatable(L, "globaltable");
lua_setmetatable(L, lib_id);
lua_setglobal(L, "globaltable");

how do i create the globaltable.subtable?

Michal Kottman · Accepted Answer · 2012-07-14 11:25:26Z

2

function is a keyword in Lua, I am guessing on how did you manage to compile the code:

-- test.lua
globaltable = { subtable = {} }
function globaltable.subtable.function()
end

When this is run:

$ lua test.lua
lua: test.lua:2: '<name>' expected near 'function'

Maybe you changed the identifiers for this online presentation, but check that on line 2 "subtable" really exists in the globaltable, because on line 3, the top of stack is already nil.

Update:

To create multiple levels of tables, you can use this approach:

lua_createtable(L,0,0); // the globaltable
lua_createtable(L,0,0); // the subtable
lua_pushcfunction(L, somefunction);
lua_setfield(L, -2, "somefunction"); // set subtable.somefunction
lua_setfield(L, -2, "subtable");     // set globaltable.subtable

edited Jul 14, 2012 at 11:25

answered Jul 14, 2012 at 9:20

Michal Kottman

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3 Comments

Vlastimil Šenfeld Over a year ago

function globaltable.subtable.function() was supposed to be just for orientation - lets assume its "function globaltable.subtable.hello()"

Michal Kottman Over a year ago

Then my second point applies. It looks like subtable cannot be found in globaltable. Try creating a Lua stackDump function to show the content of the stack, and call it after every Lua operation.

Vlastimil Šenfeld Over a year ago

Ive edited the question above - im creating this globaltable in C++ and i don't know how to create the subtable in globaltable

Vlastimil Šenfeld · Accepted Answer · 2012-07-15 10:09:42Z

0

lua_newtable(L);
luaL_newmetatable(L, "globaltable");
lua_newtable(L); //Create table
lua_setfield(L, -2, "subtable"); //Set table as field of "globaltable"
lua_setglobal(L, "globaltable");

This is what i was looking for.

answered Jul 15, 2012 at 10:09

Vlastimil Šenfeld

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