Question

After years of java, javascript, python, I am not only forget C++, but also confuse that syntax.

http://heavycoder.com/tutorials/lua_embed.php

static const luaL_reg lualibs[] =
{
        { "base",       luaopen_base },
        { NULL,         NULL }
};

lualibs init with a 2D array? luaL_reg is a type, but obviously is not a array,

const luaL_reg *lib;

for (lib = lualibs; lib->func != NULL; lib++)
{
    lib->func(l);
    lua_settop(l, 0);
}

Answer 1

luaL_reg probably looks something as the below.

typedef struct luaL_reg_t {
  char const * const name;
  void(*func)(< type_of_<l> >);
} luaL_reg;

---

The members of an object can be set using {} as in the below example, which will set the member name to point towards the location of "hello world" and func to have the adress of my_function.

luaL_reg obj = {"hello world", my_function};

---

The syntax shown in the previous snippet can also be used when initializing members of an array. In the below snippet a array of const luaL_reg instances is set to contain two objects, the first one having name = "base" and func set to luaopen_base.

To make things clear; the below is not a 2D array, but an array of const luaL_reg initialized using {} to set the members of each instance.

static const luaL_reg lualibs[] =
{
  { "base",       luaopen_base },
  { NULL,         NULL }
};

---

The last element is used to simplify iterating our array, setting both members to NULL makes it easy to see when we have reached the last element.

The loop in the upcoming snippet takes advantage of this. As long as the member func isn’t equal to NULL we haven’t gotten to the end of our array.

for (lib = lualibs; lib->func != NULL; lib++) {
  lib->func(l);
  lua_settop(l, 0);
}