CODEWITHSUNDEEP
c++lualua-table
Zack Lee
Zack Lee

Reputation: 3044

Passing table with fields as an argument to Lua function from C++?

I would like to know how to form a Lua table with fields and values so I can pass it as an argument to a Lua function from C++.

I know how to form a table using indices but I don't know how to from a table made of fields and values.

For example, I want to send this table to a Lua function as an argument from C++.

t = {xpos = 50, ypos = 80, message = 'hello'}

The below code is the closest I could get, but it's just indexed table with no field name.

lua_getglobal(L, "myLuaFunc");
if (lua_type(L, -1) == LUA_TFUNCTION)
{
    lua_newtable(L);
    lua_pushinteger(L, 1);
    lua_pushnumber(L, 50);
    lua_pushinteger(L, 2);
    lua_pushnumber(L, 80);
    lua_pushinteger(L, 3);
    lua_pushstring(L, 'hello');   
    lua_settable(L, -3);
    if (lua_pcall(L, 1, 0, 0))
        std::cout << "Error : " << lua_tostring(L, -1) << std::endl;   
}
lua_pop(L, 1);

Upvotes: 2

Views: 1787

Answers (2)

Henri Menke
Henri Menke

Reputation: 10939

I'm not sure whether I understand the question correctly. If you want strings as keys in the table, then just push strings instead of numbers.

#include <iostream>

#include <lua.hpp>

int main() {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);

    char const script[] = "function test(t)\n"
                          "    print(t.xpos)\n"
                          "    print(t.ypos)\n"
                          "    print(t.message)\n"
                          "end";

    if (luaL_dostring(L, script) != 0) {
        std::cerr << lua_tostring(L, -1) << '\n';
        lua_close(L);
        return 1;
    }

    lua_getglobal(L, "test");
    if (lua_isfunction(L, -1)) {
        lua_newtable(L);
        // xpos = 50
        lua_pushstring(L, "xpos");
        lua_pushinteger(L, 50);
        lua_settable(L, -3);
        // ypos = 80
        lua_pushstring(L, "ypos");
        lua_pushinteger(L, 80);
        lua_settable(L, -3);
        // message = "hello"
        lua_pushstring(L, "message");
        lua_pushstring(L, "hello");
        lua_settable(L, -3);

        if (lua_pcall(L, 1, 0, 0) != 0) {
            std::cerr << "lua:" << lua_tostring(L, -1) << '\n';
            lua_close(L);
            return 1;
        }
    }

    lua_close(L);
}

Upvotes: 3

lhf
lhf

Reputation: 72312

You can also use lua_setfield, which makes the code shorter and probably easier to read:

    lua_newtable(L);
    lua_pushinteger(L, 50);         // xpos = 50
    lua_setfield(L, -2, "xpos");
    lua_pushinteger(L, 80);         // ypos = 80
    lua_setfield(L, -2, "ypos");
    lua_pushstring(L, "hello");     // message = "hello"
    lua_setfield(L, -2, "message");

Upvotes: 4

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