lua-users wiki: Simple Lua Api Example (original) (raw)

/*

• test.c
• Example of a C program that interfaces with Lua.
• Based on Lua 5.0 code by Pedro Martelletto in November, 2003.
• Updated to Lua 5.1. David Manura, January 2007. */

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

int main(void) { int status, result, i; double sum; lua_State *L;

/*
 * All Lua contexts are held in this structure. We work with it almost
 * all the time.
 */
L = luaL_newstate();

luaL_openlibs(L); /* Load Lua libraries */

/* Load the file containing the script we are going to run */
status = luaL_loadfile(L, "script.lua");
if (status) {
    /* If something went wrong, error message is at the top of */
    /* the stack */
    fprintf(stderr, "Couldn't load file: %s\n", lua_tostring(L, -1));
    exit(1);
}

/*
 * Ok, now here we go: We pass data to the lua script on the stack.
 * That is, we first have to prepare Lua's virtual stack the way we
 * want the script to receive it, then ask Lua to run it.
 */
lua_newtable(L);    /* We will pass a table */

/*
 * To put values into the table, we first push the index, then the
 * value, and then call lua_rawset() with the index of the table in the
 * stack. Let's see why it's -3: In Lua, the value -1 always refers to
 * the top of the stack. When you create the table with lua_newtable(),
 * the table gets pushed into the top of the stack. When you push the
 * index and then the cell value, the stack looks like:
 *
 * <- [stack bottom] -- table, index, value [top]
 *
 * So the -1 will refer to the cell value, thus -3 is used to refer to
 * the table itself. Note that lua_rawset() pops the two last elements
 * of the stack, so that after it has been called, the table is at the
 * top of the stack.
 */
for (i = 1; i <= 5; i++) {
    lua_pushnumber(L, i);   /* Push the table index */
    lua_pushnumber(L, i*2); /* Push the cell value */
    lua_rawset(L, -3);      /* Stores the pair in the table */
}

/* By what name is the script going to reference our table? */
lua_setglobal(L, "foo");

/* Ask Lua to run our little script */
result = lua_pcall(L, 0, LUA_MULTRET, 0);
if (result) {
    fprintf(stderr, "Failed to run script: %s\n", lua_tostring(L, -1));
    exit(1);
}

/* Get the returned value at the top of the stack (index -1) */
sum = lua_tonumber(L, -1);

printf("Script returned: %.0f\n", sum);

lua_pop(L, 1);  /* Take the returned value out of the stack */
lua_close(L);   /* Cya, Lua */

return 0;

}