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Creating a simple table with Lua tables C API

Tags:

c

api

lua

I'm running a MySQL query which always returns 4 rows:

row->name, row->date, row->ip, row->custom

What I want to achieve is create a simple table basing on the above results so it would look like:

{
     "name" = result of row->name,
     "date" = result of row->date,
     "ip"   = result of row->ip,
     "custom" = result of row->custom
}

I have tried multiple possibilities, but the examples posted are really varied and I got a problems making it working.

My last unsuccessful try:

lua_createtable(L, 0, 4);
top = lua_gettop(L);
lua_pushstring(L, "name");
lua_pushstring(L, row->name);
lua_pushstring(L, "date");
lua_pushnumber(L, row->date);
lua_pushstring(L, "ip");
lua_pushstring(L, row->ip);
lua_pushstring(L, "custom");
lua_pushstring(L, row->custom);
lua_settable(L, top);
like image 370
Lucas Avatar asked Nov 22 '13 14:11

Lucas


1 Answers

As I mentioned in comment, lua_settable() takes care only of one key, value pair. Must repeat that if You need more.

I'd prefer saving the Lua stack space like this:

lua_createtable(L, 0, 4);

lua_pushstring(L, "name");
lua_pushstring(L, row->name);
lua_settable(L, -3);  /* 3rd element from the stack top */

lua_pushstring(L, "date");
lua_pushstring(L, row->date);
lua_settable(L, -3);

lua_pushstring(L, "ip");
lua_pushstring(L, row->ip);
lua_settable(L, -3);

lua_pushstring(L, "custom");
lua_pushstring(L, row->custom);
lua_settable(L, -3);

/* We still have table left on top of the Lua stack. */

Also, You could write some kind of C struct iterator or something.

NOTE: if this is for some kind of Lua wrapper - You should ensure standardized way of doing that. In the following example applied @lhf comment about shortening it a bit:

int 
l_row_push(lua_State *l)
{
    lua_createtable(L, 0, 4); /* creates and pushes new table on top of Lua stack */

    lua_pushstring(L, row->name); /* Pushes table value on top of Lua stack */
    lua_setfield(L, -2, "name");  /* table["name"] = row->name. Pops key value */

    lua_pushstring(L, row->date);
    lua_setfield(L, -2, "date");

    lua_pushstring(L, row->ip);
    lua_setfield(L, -2, "ip");

    lua_pushstring(L, row->custom);
    lua_setfield(L, -2, "custom");

    /* Returning one table which is already on top of Lua stack. */
    return 1;
}

EDIT: Fixes usage of lua_setfield() by @lhf note. Thanks!

like image 83
Kamiccolo Avatar answered Oct 17 '22 23:10

Kamiccolo