Create a table with table keys in Lua with the C API

Question

In Lua, you can create a table whose keys are themselves tables:

t = {}
t[{1,2}] = 2

I would like to know how to do the analogous thing using the C API. That is, I am writing a C function callable from Lua, which will return a table with table keys. I tried to push a table as a key and then use lua_settable, but it seems to do nothing.

Edit: Relevant code:

lua_createtable(L, 0, n);
for(i = 0; i < n; ++i){
    // push the key table
    lua_createtable(L, 2, 0);
    for(j = 0; j < 2; ++j){
        lua_pushinteger(L, j+1);
        lua_pushinteger(L, j);
        lua_settable(L, -3);
    }
    // push the value table
    lua_createtable(L, 4, 0);
    for(j = 0; j < 4; ++j){
        lua_pushinteger(L, j+1);
        lua_pushnumber(L, j);
        lua_settable(L, -3);
    }
    lua_settable(L, -3);
}

Edit: I was being dumb; I used lua_objlen(L, -1) at the end to check on the size of the table, which returns 0 since there are no integer keyed entries. Also, in the Lua code that processed the table, I used ipairs instead of pairs. Silly mistake.

Puppy Puppy · Accepted Answer · 2010-07-23T21:35:33

Pushing a table as the key and using lua_settable is the right thing to do. Most likely, you just forgot to also push on a value and did effectively t = { {} = nil }, which is of course nothing.

Create a table with table keys in Lua with the C API

2 Answers