Lua通過標準庫實現了核心之外的功能，如math庫，I/O庫等。

標準庫由C語言函數實現，提供給Lua程序使用。Lua程序與C函數通過虛擬棧交互。Lua將參數壓入棧中，C函數從棧中獲取參數，并將結果壓入棧中，C函數返回入棧的結果數量。C函數無需在壓入結果前清空棧，Lua會在函數執行完成后從棧中獲取結果并自動清空結果下的內容。

/*** $Id: lmathlib.c,v 1.67.1.1 2007/12/27 13:02:25 roberto Exp $** Standard mathematical library** See Copyright Notice in lua.h*/#include <stdlib.h>#include <math.h>#define lmathlib_c#define LUA_LIB#include "lua.h"#include "lauxlib.h"#include "lualib.h"#undef PI#define PI (3.14159265358979323846)#define RADIANS_PER_DEGREE (PI/180.0)//lua將待轉換的數字放入到lua棧，然后luaL_checknumber判斷能否轉換為數字，//能的話返回給fabs進行處理，然后將處理的結果push到lua棧中static int math_abs (lua_State *L) {  lua_pushnumber(L, fabs(luaL_checknumber(L, 1)));  return 1;}static int math_sin (lua_State *L) {  lua_pushnumber(L, sin(luaL_checknumber(L, 1)));  return 1;}static int math_sinh (lua_State *L) {  lua_pushnumber(L, sinh(luaL_checknumber(L, 1)));  return 1;}static int math_cos (lua_State *L) {  lua_pushnumber(L, cos(luaL_checknumber(L, 1)));  return 1;}static int math_cosh (lua_State *L) {  lua_pushnumber(L, cosh(luaL_checknumber(L, 1)));  return 1;}static int math_tan (lua_State *L) {  lua_pushnumber(L, tan(luaL_checknumber(L, 1)));  return 1;}static int math_tanh (lua_State *L) {  lua_pushnumber(L, tanh(luaL_checknumber(L, 1)));  return 1;}static int math_asin (lua_State *L) {  lua_pushnumber(L, asin(luaL_checknumber(L, 1)));  return 1;}static int math_acos (lua_State *L) {  lua_pushnumber(L, acos(luaL_checknumber(L, 1)));  return 1;}static int math_atan (lua_State *L) {  lua_pushnumber(L, atan(luaL_checknumber(L, 1)));  return 1;}static int math_atan2 (lua_State *L) {  lua_pushnumber(L, atan2(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_ceil (lua_State *L) {  lua_pushnumber(L, ceil(luaL_checknumber(L, 1)));  return 1;}static int math_floor (lua_State *L) {  lua_pushnumber(L, floor(luaL_checknumber(L, 1)));  return 1;}static int math_fmod (lua_State *L) {  lua_pushnumber(L, fmod(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_modf (lua_State *L) {  double ip;  double fp = modf(luaL_checknumber(L, 1), &ip);  lua_pushnumber(L, ip);  lua_pushnumber(L, fp);  return 2;}static int math_sqrt (lua_State *L) {  lua_pushnumber(L, sqrt(luaL_checknumber(L, 1)));  return 1;}static int math_pow (lua_State *L) {  lua_pushnumber(L, pow(luaL_checknumber(L, 1), luaL_checknumber(L, 2)));  return 1;}static int math_log (lua_State *L) {  lua_pushnumber(L, log(luaL_checknumber(L, 1)));  return 1;}static int math_log10 (lua_State *L) {  lua_pushnumber(L, log10(luaL_checknumber(L, 1)));  return 1;}static int math_exp (lua_State *L) {  lua_pushnumber(L, exp(luaL_checknumber(L, 1)));  return 1;}static int math_deg (lua_State *L) {  lua_pushnumber(L, luaL_checknumber(L, 1)/RADIANS_PER_DEGREE);  return 1;}static int math_rad (lua_State *L) {  lua_pushnumber(L, luaL_checknumber(L, 1)*RADIANS_PER_DEGREE);  return 1;}static int math_frexp (lua_State *L) {  int e;  lua_pushnumber(L, frexp(luaL_checknumber(L, 1), &e));  lua_pushinteger(L, e);  return 2;}static int math_ldexp (lua_State *L) {  lua_pushnumber(L, ldexp(luaL_checknumber(L, 1), luaL_checkint(L, 2)));  return 1;}static int math_min (lua_State *L) {  int n = lua_gettop(L);  /* number of arguments */  lua_Number dmin = luaL_checknumber(L, 1);  int i;  for (i=2; i<=n; i++) {    lua_Number d = luaL_checknumber(L, i);    if (d < dmin)      dmin = d;  }  lua_pushnumber(L, dmin);  return 1;}static int math_max (lua_State *L) {  int n = lua_gettop(L);  /* number of arguments */  lua_Number dmax = luaL_checknumber(L, 1);  int i;  for (i=2; i<=n; i++) {    lua_Number d = luaL_checknumber(L, i);    if (d > dmax)      dmax = d;  }  lua_pushnumber(L, dmax);  return 1;}static int math_random (lua_State *L) {  /* the `%' avoids the (rare) case of r==1, and is needed also because on     some systems (SunOS!) `rand()' may return a value larger than RAND_MAX */  lua_Number r = (lua_Number)(rand()%RAND_MAX) / (lua_Number)RAND_MAX;  switch (lua_gettop(L)) {  /* check number of arguments */    case 0: {  /* no arguments */      lua_pushnumber(L, r);  /* Number between 0 and 1 */      break;    }    case 1: {  /* only upper limit */      int u = luaL_checkint(L, 1);      luaL_argcheck(L, 1<=u, 1, "interval is empty");      lua_pushnumber(L, floor(r*u)+1);  /* int between 1 and `u' */      break;    }    case 2: {  /* lower and upper limits */      int l = luaL_checkint(L, 1);      int u = luaL_checkint(L, 2);      luaL_argcheck(L, l<=u, 2, "interval is empty");      lua_pushnumber(L, floor(r*(u-l+1))+l);  /* int between `l' and `u' */      break;    }    default: return luaL_error(L, "wrong number of arguments");  }  return 1;}static int math_randomseed (lua_State *L) {  srand(luaL_checkint(L, 1));  return 0;}static const luaL_Reg mathlib[] = {  {"abs",   math_abs},  {"acos",  math_acos},  {"asin",  math_asin},  {"atan2", math_atan2},  {"atan",  math_atan},  {"ceil",  math_ceil},  {"cosh",   math_cosh},  {"cos",   math_cos},  {"deg",   math_deg},  {"exp",   math_exp},  {"floor", math_floor},  {"fmod",   math_fmod},  {"frexp", math_frexp},  {"ldexp", math_ldexp},  {"log10", math_log10},  {"log",   math_log},  {"max",   math_max},  {"min",   math_min},  {"modf",   math_modf},  {"pow",   math_pow},  {"rad",   math_rad},  {"random",     math_random},  {"randomseed", math_randomseed},  {"sinh",   math_sinh},  {"sin",   math_sin},  {"sqrt",  math_sqrt},  {"tanh",   math_tanh},  {"tan",   math_tan},  {NULL, NULL}};//當在Lua程序中，調用require("math")時，就會調用下面的luaopen_math函數，來注冊函數庫//lua5.1 之中有一個luaL_register,用于把luaL_Reg 數組中的所有函數注冊到lua中。但在lua5.2中已經不支持這一函數了//lua_setfield設置lua棧中的值//HUGE_VAL是C語言在<error.h>定義的一個非常大的double正數。LUALIB_API int luaopen_math (lua_State *L) {  luaL_register(L, LUA_MATHLIBNAME, mathlib);  lua_pushnumber(L, PI);  lua_setfield(L, -2, "pi");  lua_pushnumber(L, HUGE_VAL);  lua_setfield(L, -2, "huge");#if defined(LUA_COMPAT_MOD)  lua_getfield(L, -1, "fmod");  lua_setfield(L, -2, "mod");#endif  return 1;}
結構體實例mathlib中保存了lua函數庫所有的接口，結構體luaL_Reg在lauxlib.h中的定義的：typedef struct luaL_Reg {const char *name;lua_CFunction func;} luaL_Reg;這里的函數類型lua_CFunction在lua.h中定義的：typedef int (*lua_CFunction) (lua_State *L);所有用C實現的Lua函數，都是必須是這種類型，即一個lua_State的參數，返回值為int。
HUGE_VAL是C語言在<error.h>定義的一個非常大的double正數。