Hydra: ProgrammingWithLuaAndC

Programming with Lua and or C

1. Development Tools: 1.1 Introduction; 1.2 Programming with Lua and or C; 1.3 Working with Premake; 1.4 Bmake; 1.5 Debugging; 1.6 Using Fossil (DVCS); 1.7 Further Reading

Using C Library's in Pure Lua (Simple)

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local ffi = require("ffi")
ffi.cdef[[
int printf(const char *fmt, ...);
]]
ffi.C.printf("Hello %s!", "world")

Using C Library's in Pure Lua (Advanced)

The following code shows how to access the zlib compression library from Lua code.


local ffi = require("ffi")
ffi.cdef[[
unsigned long compressBound(unsigned long sourceLen);
int compress2(uint8_t *dest, unsigned long *destLen,
	      const uint8_t *source, unsigned long sourceLen, int level);
int uncompress(uint8_t *dest, unsigned long *destLen,
	       const uint8_t *source, unsigned long sourceLen);
]]

local zlib = ffi.load(ffi.os == "Windows" and "zlib1" or "z")

C++ and Lua Hybrid Application

The following example uses LuaWrapper and Luajit.

LuaWrapper is a library designed to help bridge the gab between Lua and C++. It is designed to be small (a single header file), simple, fast, and typesafe. It has no external dependencies other than the lua library itself, and does not need to be precompiled; the header can simply be dropped into a project and used immediately. It even supports class inheritance to a certain degree. Objects can be created in either Lua or C++, and passed back and forth.

The nice thing about LuaWrapper is that we can develop our C++ and Lua frameworks side by side and still keep them separate.

main.cpp

#include <iostream>
extern "C"
{
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
#include "luajit.h"
}

#include "LuaBankAccount.hpp"

using namespace std;

int main(int argc, const char *argv[])
{
    if (argc == 2)
    {
        lua_State* L = luaL_newstate();
        luaJIT_setmode(L, -1, LUAJIT_MODE_WRAPCFUNC|LUAJIT_MODE_ON);
        luaL_openlibs(L);
        luaopen_BankAccount(L);
        if (luaL_dofile(L, argv1))
            cout << lua_tostring(L, -1) << endl;
        lua_close(L);
    }
    return 0;
}

BankAccount.cpp

#include <BankAccount.hpp>

float BankAccount::s_totalMoneyInBank = 0;

BankAccount::BankAccount(const char* owner, float balance) 
    : m_owner(owner)
    , m_balance(balance)
{
    s_totalMoneyInBank += balance;
}

const char* BankAccount::getOwnerName() const
{
    return m_owner;
}

void BankAccount::deposit(float amount)
{
    s_totalMoneyInBank += amount;
    m_balance += amount;
}

void BankAccount::withdraw(float amount)
{
    s_totalMoneyInBank -= amount;
    m_balance -= amount;
}

float BankAccount::checkBalance() const
{
    return m_balance;
}

float BankAccount::checkTotalMoneyInBank()
{
    return s_totalMoneyInBank;
}

BankAccount.hpp

#ifndef EXAMPLE_HPP_
#define EXAMPLE_HPP_

#include <string>
#include <iostream>

class BankAccount
{
public:
    BankAccount(const char* owner, float balance);

    const char* getOwnerName() const;
    void deposit(float amount);
    void withdraw(float amount);
    float checkBalance() const;
    
    static float checkTotalMoneyInBank();
    
private:
    const char* m_owner;
    float m_balance;
    static float s_totalMoneyInBank;
};

#endif // EXAMPLE_HPP_

LuaBankAccount.cpp

#include <iostream>
#include <string>

extern "C"
{
#include "lua.h"
#include "lauxlib.h"
}
#include "luawrapper.hpp"

#include "BankAccount.hpp"

using namespace std;

//
// Allocator
//
// Types that do not have a default contructor require you to write an allocator function.
// This function is passed to luaW_register.
//

BankAccount* BankAccount_new(lua_State *L)
{
    const char* owner = luaL_checkstring(L, 1);
    float balance = luaL_checknumber(L, 2);
    return new BankAccount(owner, balance);
}

//
// Static Functions
//
// These functions can be called directly from the BankAccount table in lua
//

int BankAccount_checkTotalMoneyInBank(lua_State *L)
{
    lua_pushnumber(L, BankAccount::checkTotalMoneyInBank());
    return 1;
}

//
// Member Functions
//
// These functions are stored on the BankAccount.metatable table.
// All BankAccount objects in Lua have access to the functions defined there
// by the use of special a __index metatmethod that is set up by LuaWrapper.
//

int BankAccount_getOwnerName(lua_State *L)
{
    BankAccount* account = luaW_check(L, 1);
    lua_pushstring(L, account->getOwnerName());
    return 1;
}

int BankAccount_deposit(lua_State *L)
{
    BankAccount* account = luaW_check(L, 1);
    float amount = luaL_checknumber(L, 2);
    account->deposit(amount);
    return 0;
}

int BankAccount_withdraw(lua_State *L)
{
    BankAccount* account = luaW_check(L, 1);
    float amount = luaL_checknumber(L, 2);
    account->withdraw(amount);
    return 0;
}

int BankAccount_checkBalance(lua_State *L)
{
    BankAccount* account = luaW_check(L, 1);
    lua_pushnumber(L, account->checkBalance());
    return 1;
}

static luaL_Reg BankAccount_table[] =
{
    { "checkTotalMoneyInBank", BankAccount_checkTotalMoneyInBank },
    { NULL, NULL }
};

static luaL_Reg BankAccount_metatable[] =
{
    { "getOwnerName", BankAccount_getOwnerName },
    { "deposit", BankAccount_deposit },
    { "withdraw", BankAccount_withdraw },
    { "checkBalance", BankAccount_checkBalance },
    { NULL, NULL }
};

int luaopen_BankAccount(lua_State* L)
{
    luaW_register(L,
        "BankAccount",
        BankAccount_table,
        BankAccount_metatable,
        BankAccount_new // If your class has a default constructor you can omit this argument,
                        // LuaWrapper will generate a default allocator for you.
    );
    return 1;
}

LuaBankAccount.hpp

#ifndef LUAEXAMPLE_HPP_
#define LUAEXAMPLE_HPP_

struct lua_State;

int luaopen_BankAccount(lua_State*);

#endif // LUAEXAMPLE_HPP_

example1.lua

alicesaccount = BankAccount.new("Alice", 100)

alicesaccount:deposit(20);
alicesaccount:deposit(30);
alicesaccount:deposit(40);

bobsaccount = BankAccount.new("Bob", 200)

bobsaccount:withdraw(10);
bobsaccount:withdraw(15);
bobsaccount:withdraw(20);

function printaccountbalance(account)
    local name = account:getOwnerName()
    local balance = account:checkBalance()
    print(string.format("%s has $%d", name, balance))
end

printaccountbalance(alicesaccount)
printaccountbalance(bobsaccount)

print(string.format("The bank has $%d", BankAccount.checkTotalMoneyInBank()))