Compile lua code, store bytecode then load and execute it

Question

I'm trying to compile a lua script that calls some exported functions, save the resulting bytecode to a file and then load this bytecode and execute it, but I haven't found any example on how to do this. Is there any example available on how to do this? How can I do this?

Edit: I'm using Lua + Luabind (C++)

Solution

This is all very simple.

First, you load the Lua script without executing it. It does not matter if you have connected the Lua state with your exported functions; all you're doing is compiling the script file.

You could use luaL_loadfile, which uses C-standard library functions to read a file from disk and load it into the lua_State. Alternatively, you can load the file yourself into a string and use luaL_loadstring to load it into the lua_State.

Both of these functions will emit return values and compiler errors as per the documentation for lua_load.

If the compilation was successful, the lua_State now has the compiled Lua chunk as a Lua function at the top of the stack. To get the compiled binary, you must use the lua_dump function. It's rather complicated as it uses a callback interface to pass you data. See the documentation for details.

After that process, you have the compiled Lua byte code. Shove that into a file of your choice. Just remember: write it as binary, not with text translation.

When it comes time to load the byte code, all you need to do is... exactly what you did before. Well, almost. Lua has heuristics to detect that a "string" it is given is a Lua source string or byte code. So yes, you can load byte code with luaL_loadfile just like before.

The difference is that you can't use luaL_loadstring with byte code. That function expects a NULL-terminated string, which is bad. Byte code can have embedded NULL characters in it, which would screw everything up. So if you want to do the file IO yourself (because you're using a special filesystem or something), you have to use lua_load directly (or luaL_loadbuffer). Which also uses a callback interface like lua_dump. So read up on how to use it.