attempt to call global `print' (a nil value)

Question

I have the following C file:

//thing.c
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

#include <stdio.h>

lua_State* L;

int main(){
        L = lua_open();

        lua_dostring(L, "print(\"lua\")");
        printf("hello\n");

        return 0; }

and the following makefile:

default:
        gcc -I/usr/include/lua50 -L/usr/lib -o qwerty thing.c -llua50 -llualib50

the code builds just fine, but when I run it I get the following:

[string "print("lua")"]:1: attempt to call global `print' (a nil value)
hello

Note: I have seen the many other questions on this error, but they all deal with working directly in Lua, as opposed to with the C api. They also seem to imply that the problem is that the print function was never defined. I don't understand this, as I can run both a lua interpreter and a lua script just fine directly from the command line.

EDIT: I am using lua 5.0

Answer 1

You have to initialize the libraries in Lua. After you call lua_open, call

luaL_openlibs(L);

Edit: for Lua 5.0, I believe you'll have to open the libraries manually. For the print function, you just need the base library:

luaopen_base(L);