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In the second kind, Lua has the control and C is the library. Here, the C code is called library code. The same API to communicate with Lua, the so called C API. The C program is the same as all the others except stacking arguments to Lua is a little different, and recovering the table passed back from Lua is a little different. The Lua tweaktable function takes a table as its one and only argument and passes back one table.

From a running Cprogram, you can call a Lua script. The C program can pass arguments tothe Lua script, and the Lua script can pass back a return. The Luascript can serve to initialize the C program, or the Lua script caninstall a callback routine in the C program.
Calling a Lua script from a C program can be daunting without the rightinformation. Different computers have different names and locations forlibraries and include files, and it's difficult to figure out what'scausing compile/link problems.
Further complicating things is that with every major version of Lua,the method of calling Lua from C changes. Much documentation on theInternet is specific to Lua 5.0, and won't work on 5.1. Likewise, thisdocumentation is specific to 5.1, and when 5.2 comes out (it's alpharight now), the documentation on this page won't work on the newversion.
The purpose of this document is to make it easy for you to do simple Lua calls from C programs.
A typical interaction from a C program to a Lua 5.1 script looks something like this:

Create a Lua state variable
Load Lua libraries
Load but don't run the Lua script file
Priming script run to create script's global vars
Pass all arguments to the Lua script on the stack
Run the loaded Lua script
Retrieve the return from the Lua script
Close the Lua state variable

Create a Lua state variable		lua_State *L; L = luaL_newstate();
Load Lua libraries		luaL_openlibs(L);
Load but don't run the Lua script file		luaL_loadfile(L, 'script.lua')
Priming run of the loaded Lua script to create the script's global variables
Pass all arguments to the Lua script on the stack		Various routines, too many to name.
Run the loaded Lua script
Retrieve the return from the Lua script		Various pops and stack calls
Close the Lua state variable		lua_close(L);

Header Files

Always put these three header files at the top of any C program calling Lua:

Compiling and Linking

Nothing is tougher than compiling and linking your first C to Luaprogram. There are way too many variables, it seems like everything's ablack box, and you run around changing things trial and error, crossingyour fingers.
But there's a method to the madness, and this subsection explains it.If you know all the content of this section, try not to be offended orinsulted -- the extra info is for those who don't know it yet.
Here's a typical command to compile it:
Let's break that down:

	Your systems C compilation command. Could be cc, or gcc, or something else.
	Show all warnings. You might choose not to insert this until all other errors and warnings have been fixed.
	The name of the finished executable.
	The name of the C file to compile.
	Every C compiler checks for include files in certain places. But often lua.h, liblua.h and lauxlua.h aren't in those places, so you need to tell the compiler where to find them.
	Every C compiler checks for libraries to link in certainplaces. But often the Lua libraries are elsewhere, so you need to tellthe compiler where to find them.
	Link in the Lua library. The way you name this library in the compiler's -l option requires some thought and research, which will be explained later in this subsection.
	Link in the math library (often not necessary)

The Process of Finding the Right Compile Command

Finding the right compile command is a process that looks something like this:

Try to compile, no link, no -Wall, no -I. You might get lucky.
Find the location of the Lua include files.
Using that location, compile, no link, no -Wall.
Compile, no link, use -Wall.
Find the location and filenames of the Lua library files.
Using the location and filenames, compile and link.
Test the Executable.

Step 1: Try to compile, no link, no -Wall, no -I

Do this:
Notice that the -c means 'compile only, do not link'. Sometimes it'snot all that clear whether an error or warning comes from compile orlink, but it's very clear if you only compile. If the preceding commanddoesn't error out, skip to step 4. However, in my case it errored out:
On to step 2...

Step 2: Find the location of the Lua include files

The three Ubiquitous Lua include files are lua.h, lauxlib.h, and lualib.h. Use your Linux box's locate command to find lua.h after running updatedb to make sure that locate finds everything. Make sure that the directory with lua.h also contains lauxlib.h, and lualib.h.
Obviously the directory you want is /usr/include/lua5.1. Now see if that directory contains the other two:
OK, that's it. You know you need to add -I /usr/include/lua5.1 to the command.

Step 3: Using that location, compile, no link, no -Wall

In my case the preceding worked:
If it hadn't worked, and you'd included all three header files in hello.c, and you're sure you got the additional include directory right, suspect wrong code in hello.c itself. If it doesn't produce errors or warnings, go on to the next step...

Step 4: Compile, no link, use -Wall

In my case, the preceding produced no errors or warnings:
If it produces warnings, try your best to fix them. Warnings are oftena sign of problems that rear their ugly head a week after deployment.
Once you have no errors or warnings, go on to the next step...

Step 5: Find the location and filenames of the Lua library files

First a word about how the -l compiler option works. The -loption assumes every library file starts with 'lib'. Therefore, insteadof making you type -lliblua, it makes you type -llua and then out ofthe goodness of its heart prepends lib before the lua. For instance, if you put -llua, that means that it searches for a file called liblua.a or liblua.o or liblua.so, etc. So you need to find the liblua.* files. Do it as follows:
Here's the partial result:
See the ones called liblua5.1.*? Those are the Lua libraries on my computer. So we have a pretty good idea that the -l argument should be lua5.1.We also know that they're located in /usr/lib, which probably isalready on the C compiler's library path, so we probably don't need a -L compiler option. If these files had been in /usr/lib/lua, we'd have needed an -L option.

Step 6: Using the location and filenames, compile and link

This step differs from step 4 in two ways:

We remove the -c so that it will attempt to link
We add -llua5.1

Here we go...
It worked. If it hadn't, we'd have been forced to troubleshoot.

Step 7: Test the Executable

So let's run it:
You haven't seen the code for hello.c and helloscript.lua yet, but take it from

C In Lua