I want to create a table like
myTable = {
[0] = { ["a"] = 4, ["b"] = 2 },
[1] = { ["a"] = 13, ["b"] = 37 }
}
using the C API?
My current approach is
lua_createtable(L, 0, 2);
int c = lua_gettop(L);
lua_pushstring(L, "a");
lua_pushnumber(L, 4);
lua_settable(L, c);
lua_pushstring(L, "b");
lua_pushnumber(L, 2);
lua_settable(L, c);
to create the inner tables in a loop. Before, this loop, I use
lua_createtable(L, 2, 0);
int outertable = lua_gettop(L);
to create the outer table for 2 numeric slots.
But how can I save the inner tables to the outer table?
Here's a full and minimal program demonstrating how to nest tables. Basically what you are missing is the lua_setfield
function.
#include <stdio.h>
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
int main()
{
int res;
lua_State *L = lua_open();
luaL_openlibs(L);
lua_newtable(L); /* bottom table */
lua_newtable(L); /* upper table */
lua_pushinteger(L, 4);
lua_setfield(L, -2, "four"); /* T[four] = 4 */
lua_setfield(L, -2, "T"); /* name upper table field T of bottom table */
lua_setglobal(L, "t"); /* set bottom table as global variable t */
res = luaL_dostring(L, "print(t.T.four == 4)");
if(res)
{
printf("Error: %s\n", lua_tostring(L, -1));
}
return 0;
}
The program will simply print true
.
If you need numeric indices, then you continue using lua_settable
:
#include <stdio.h>
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
int main()
{
int res;
lua_State *L = lua_open();
luaL_openlibs(L);
lua_newtable(L); /* bottom table */
lua_newtable(L); /* upper table */
lua_pushinteger(L, 0);
lua_pushinteger(L, 4);
lua_settable(L, -3); /* uppertable[0] = 4; pops 0 and 4 */
lua_pushinteger(L, 0);
lua_insert(L, -2); /* swap uppertable and 0 */
lua_settable(L, -3); /* bottomtable[0] = uppertable */
lua_setglobal(L, "t"); /* set bottom table as global variable t */
res = luaL_dostring(L, "print(t[0][0] == 4)");
if(res)
{
printf("Error: %s\n", lua_tostring(L, -1));
}
return 0;
}
Rather than using absolute indices of 0 like I did, you might want to use lua_objlen
to generate the index.
For simple code like the one you gave, my lua2c works fine and generates the code below.
/* This C code was generated by lua2c from the Lua code below.
myTable = {
[0] = { ["a"] = 4, ["b"] = 2 },
[1] = { ["a"] = 13, ["b"] = 37 }
}
*/
static int MAIN(lua_State *L)
{
lua_newtable(L);
lua_pushnumber(L,0);
lua_newtable(L);
lua_pushliteral(L,"a");
lua_pushnumber(L,4);
lua_pushliteral(L,"b");
lua_pushnumber(L,2);
lua_settable(L,-5);
lua_settable(L,-3);
lua_pushnumber(L,1);
lua_newtable(L);
lua_pushliteral(L,"a");
lua_pushnumber(L,13);
lua_pushliteral(L,"b");
lua_pushnumber(L,37);
lua_settable(L,-5);
lua_settable(L,-3);
lua_settable(L,-5);
lua_settable(L,-3);
lua_setglobal(L,"myTable");
return 0;
}
Here is something generic I came up to solve a similar problem, based on lhf's answer. This will create a Lua table for the form
{
{"foo"},
{"bar", "baz"}
}
With arbitrary table/sub table length.
int list_of_lists_to_lua(lua_State* L, const std::vector<std::vector<std::string>>& convertme) {
lua_newtable(L);
int counter = 0;
for (const std::vector<std::string>& list : convertme) {
lua_pushnumber(L, ++counter);
lua_newtable(L);
int counter2 = 0;
for (const std::string& item : list) {
lua_pushnumber(L, ++counter2);
lua_pushstring(L, item);
lua_settable(L,-3);
}
lua_settable(L,-3);
}
return 1;
}
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