How do you pass the Lua function to the C function and execute the Lua function several times?

Question

I want to create a function that will iterate over some objects and call a function for each function. I use BlitzMax, not C, but it is not, because it has the full shell of Lua C functions. Lua has the lua_pushcfunction () command, but where is the lua_pushfunction () command? It is very easy to call functions that have a name, but what do you call a function that was passed as an argument?

Sort of:

ForEach( PlanetList, function (planet)
    if(planet.exists == true) then
        Planet_Count = Planet_Count + 1
    end
end )

Usually you just say "lua_getglobal (L, name)" and it positions the lua function perfectly on the stack, but how do you get it from the argument?

EDIT

I came back and actually tried to use luaL_ref()from this question that I found earlier . What I am doing is using luaL_ref () to print the function value from the top of the stack and put it in a temporary register, I used the value returned from luaL_ref()to use lua_rawgeti()for each of the items in the list, And then used luaL_unref()after the list was completed to free this register.

Answer 1

I had the same question since I am new to Lua. Since, in my opinion, there was no satisfactory answer, I decided that I would write it, although this question may never be closed. Hope this helps someone else in this situation.

main.c

#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

/* this keeps our Lua reference to the Lua function */
int callback_reference = 0;

/* this is called by Lua to register its function */
int lua_registerCallback( lua_State *L ) {

  /* store the reference to the Lua function in a variable to be used later */
  callback_reference = luaL_ref( L, LUA_REGISTRYINDEX );

  return 0;
}

/* calls our Lua callback function and resets the callback reference */
void call_callback( lua_State *L ) {

  /* push the callback onto the stack using the Lua reference we */
  /*  stored in the registry */
  lua_rawgeti( L, LUA_REGISTRYINDEX, callback_reference );

  /* duplicate the value on the stack */
  /* NOTE: This is unnecessary, but it shows how you keep the */
  /*  callback for later */
  lua_pushvalue( L, 1 );

  /* call the callback */
  /* NOTE: This is using the one we duplicated with lua_pushvalue */
  if ( 0 != lua_pcall( L, 0, 0, 0 ) ) {
    printf("Failed to call the callback!\n %s\n", lua_tostring( L, -1 ) );
    return;
  }

  /* get a new reference to the Lua function and store it again */
  /* NOTE: This is only used in conjunction with the lua_pushvalue */
  /*  above and can be removed if you remove that */
  callback_reference = luaL_ref( L, LUA_REGISTRYINDEX );
}

int main( void ) {

  /* set up Lua */
  lua_State *L = lua_open();
  luaL_openlibs( L );

  /* register the lua_registerCallback function as */
  /*  "RegisterCallback" so it can be called by Lua */
  lua_pushcfunction( L, lua_registerCallback );
  lua_setglobal( L, "RegisterCallback" );

  /* run our Lua file */
  if ( 0 != luaL_dofile( L, "callback.lua" ) ) {
    printf("Failed to load calback.lua!\n %s",
      lua_tostring( L, -1 ) );
    lua_close( L );
    return 1;
  }

  /* call the callback */
  call_callback( L );

  /* call the callback again if you want (because we restored */
  /*  the Lua function reference) */
  call_callback( L );

  /* remove the reference to the callback */
  /* NOTE: This is also unnecessary if you didn't re-add the */
  /*  function to the registry */
  luaL_unref( L, LUA_REGISTRYINDEX, callback_reference );

  /* uninitialize Lua */
  lua_close( L );

  return 0;
}

callback.lua

function MyCallback()
  print("Hello World!")
end

RegisterCallback( MyCallback )

Answer 2

lua_pushvalue, , .

: lua_pushvalue() , , lua_pcall() lua_call() .