2007 01 31 Simplecppluabinding Lua Users Mirror

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This is attach to site 2007-01-31 Simple C++ Lua Binding

Just a copy of tutorial from http://lua-users.org/wiki/SimpleCppBinding

Simple Cpp Binding

Description

Here is an example of a Lua binding for a simple C++ class. If you prefer, you can factor out all the nasty bits and put then in a template. SimplerCppBinding shows how to do this using Luna for Lua 5.0

C++ code

extern "C" {
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
}

class Account {
public:
Account(double balance) { m_balance = balance; }
void deposit(double amount) { m_balance += amount; }
void withdraw(double amount) { m_balance -= amount; }
double balance(void) { return m_balance; }
private:
double m_balance;
};

class LuaAccount {
static const char className[];
static const luaL_reg methods[];

static Account *checkaccount(lua_State *L, int narg) {
luaL_checktype(L, narg, LUA_TUSERDATA);
void *ud = luaL_checkudata(L, narg, className);
if(!ud) luaL_typerror(L, narg, className);
return *(Account**)ud; // unbox pointer
}

static int create_account(lua_State *L) {
double balance = luaL_checknumber(L, 1);
Account *a = new Account(balance);
lua_boxpointer(L, a);
luaL_getmetatable(L, className);
lua_setmetatable(L, -2);
return 1;
}
static int deposit(lua_State *L) {
Account *a = checkaccount(L, 1);
double amount = luaL_checknumber(L, 2);
a->deposit(amount);
return 0;
}
static int withdraw(lua_State *L) {
Account *a = checkaccount(L, 1);
double amount = luaL_checknumber(L, 2);
a->withdraw(amount);
return 0;
}
static int balance(lua_State *L) {
Account *a = checkaccount(L, 1);
double balance = a->balance();
lua_pushnumber(L, balance);
return 1;
}
static int gc_account(lua_State *L) {
Account *a = (Account*)lua_unboxpointer(L, 1);
delete a;
return 0;
}

public:
static void Register(lua_State* L) {
lua_newtable(L); int methodtable = lua_gettop(L);
luaL_newmetatable(L, className); int metatable = lua_gettop(L);

lua_pushliteral(L, "__metatable");
lua_pushvalue(L, methodtable);
lua_settable(L, metatable); // hide metatable from Lua getmetatable()

lua_pushliteral(L, "__index");
lua_pushvalue(L, methodtable);
lua_settable(L, metatable);

lua_pushliteral(L, "__gc");
lua_pushcfunction(L, gc_account);
lua_settable(L, metatable);

lua_pop(L, 1); // drop metatable

luaL_openlib(L, 0, methods, 0); // fill methodtable
lua_pop(L, 1); // drop methodtable

lua_register(L, className, create_account);
}
};

const char LuaAccount::className[] = "Account";

#define method(class, name) {#name, class::name}

const luaL_reg LuaAccount::methods[] = {
method(LuaAccount, deposit),
method(LuaAccount, withdraw),
method(LuaAccount, balance),
{0,0}
};

int main(int argc, char* argv[])
{
lua_State *L = lua_open();

luaopen_base(L);
luaopen_table(L);
luaopen_io(L);
luaopen_string(L);
luaopen_math(L);
luaopen_debug(L);

LuaAccount::Register(L);

if(argc>1) lua_dofile(L, argv[1]);

lua_close(L);
return 0;
}

Compiling the Code

This code can be compiled for Lua 5.0 as follows:

g++ -o test account.cc -L/usr/local/lib -llua -llualib

Lua Test Code

function printf(…) io.write(string.format(unpack(arg))) end

local a = Account(100)
printf("Account balance = $%0.02f\n", a:balance() )
a:deposit(50.30)
printf("Account balance = $%0.02f\n", a:balance() )
a:withdraw(25.10)
printf("Account balance = $%0.02f\n", a:balance() )

Test Code Output

$ ./test account.lua
Account balance = $100.00
Account balance = $150.30
Account balance = $125.20

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