Implement lua scripting through dll calls?

Question

Is it possible to write a program that can execute lua scripts just by using the lua52.dll file?
Or do I have to create a new C project and use all these header and source files?
I just want to create a few global variables and functions and make them available in the lua scripts that should be executed.
So in theory:

LoadDll("lua52.dll")
StartLua()
AddFunctionToLua("MyFunction1")
AddFunctionToLua("MyFunction2")
AddVariableToLua("MyVariable1")
...
ExecuteLuaScript("C:\myScript.lua")
CloseLua()

With the proper macros the code above can be turned into valid C code that call the Lua API. But this C code still needs to be compiled into you application. And the functions you export to Lua must be what the Lua API expects, though you probably can get avoid this by using an FFI such as the one in LuaJIT. — lhf
Yes, and your MyFunction1 etc could be written in C, C++, C# etc, Java, and, of course, Lua. I presume you had one in mind. You'll get better answers if you say which and give more context. — Tom Blodget

RBerteig RBerteig · Accepted Answer · 2013-10-14T20:49:39

The standard command line interpreter for Lua is an example of just such a program. On windows, it is a small executable that is linked to lua52.dll. Its source is, of course, part of the Lua distribution.

Despite being located in the same folder as the sources to the Lua DLL, lua.c only references the public API for Lua, and depends only on the four public header files and the DLL itself.

An even simpler example that embeds a Lua interpreter in a C program is the following, derived from the example shown in the PiL book available online:

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

int main (void) {
    char buff[256];
    int error;
    lua_State *L = luaL_newstate();  /* create state */
    luaL_openlibs(L);                /* open standard libraries */

    while (fgets(buff, sizeof(buff), stdin) != NULL) {
        error = luaL_loadbuffer(L, buff, strlen(buff), "line") ||
                lua_pcall(L, 0, 0, 0);
        if (error) {
            fprintf(stderr, "%s", lua_tostring(L, -1));
            lua_pop(L, 1);  /* pop error message from the stack */
        }
    }

    lua_close(L);
    return 0;
}

In your existing application, you would need to call luaL_newstate() once and store the returned handle. Along with a call to luaL_openlibs(), you would likely want to also define one or more Lua modules representing your application's scriptable API. And of course, you need to call lua_close() sometime before exiting so that Lua has a chance to clean up its objects and in particular a chance to deal with any objects that the script authors are depending on to get resources released when the application exits.

With that in place, you generally provide a way to load script fragments provided by your user using luaL_loadbuffer() or any of several other functions built on top of lua_load(). Loading a script compiles it and leaves an anonymous function on the top of the stack that when called will execute all top-level statements in the script.

For a lot more discussion of this, see the chapters of Programming in Lua (an older addition is available online) that relate to the C API.

Implement lua scripting through dll calls?

2 Answers