Description

Luna (see SimplerCppBinding) is good for calling C++ functions from Lua. But if you wish to call Lua functions from C++, then you'll need to stash your Lua function in a sub-table of either the registry or the table of globals, and then use lua_pcall to invoke it from your C++ code. This example uses Lunar (see CppBindingWithLunar) which is a revised version of Luna that makes this a bit easier.

You can find lunar.h on the CppBindingWithLunar page.

account.cc C++ code

extern "C" {
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
}
#include "lunar.h"
class Account {
 lua_Number m_balance;
public:
 Account(double balance=0) : m_balance(balance) { }
 void deposit(double amount) { m_balance += amount; }
 void withdraw(double amount) { m_balance -= amount; }
 double balance(void) { return m_balance; }
 ~Account() { printf("deleted Account (%p)\n", this); }
 // Lua interface
 Account(lua_State *L) : m_balance(luaL_checknumber(L, 1)) { }
 int deposit (lua_State *L) { deposit (luaL_checknumber(L, 1)); return 0; }
 int withdraw(lua_State *L) { withdraw(luaL_checknumber(L, 1)); return 0; }
 int balance (lua_State *L) { lua_pushnumber(L, balance()); return 1; }
 static const char className[];
 static Lunar<Account>::RegType methods[];
};
const char Account::className[] = "Account";
#define method(class, name) {#name, &class::name}
Lunar<Account>::RegType Account::methods[] = {
 method(Account, deposit),
 method(Account, withdraw),
 method(Account, balance),
 {0,0}
};
static int report (lua_State *L, int status)
{
 if (status) {
 const char *msg = lua_tostring(L, -1);
 if (msg == NULL) msg = "(error with no message)";
 fprintf(stderr, "ERROR: %s\n", msg);
 lua_pop(L, 1);
 }
 return status;
}
static int application (lua_State *L)
{
 lua_settop(L, 0);
 lua_pushliteral(L, "_TRACEBACK");
 lua_gettable(L, LUA_GLOBALSINDEX); // get traceback function
 int tb = lua_gettop(L);
 Account a;
 Account *b = new Account(30);
 int A = Lunar<Account>::push(L, &a);
 int B = Lunar<Account>::push(L, b, true);
 lua_pushliteral(L, "a");
 lua_pushvalue(L, A);
 lua_settable(L, LUA_GLOBALSINDEX);
 lua_pushliteral(L, "b");
 lua_pushvalue(L, B);
 lua_settable(L, LUA_GLOBALSINDEX);
 lua_pushvalue(L, A);
 lua_pushnumber(L, 100.00);
 report(L, Lunar<Account>::call(L, "deposit", 1, 0, tb) < 0);
 lua_pushvalue(L, A);
 report(L, Lunar<Account>::call(L, "show", 0, 0, tb) < 0);
 lua_pushvalue(L, B);
 report(L, Lunar<Account>::call(L, "show", 0, 0, tb) < 0);
 lua_pushliteral(L, "main");
 lua_gettable(L, LUA_GLOBALSINDEX);
 report(L, lua_pcall(L, 0, 0, tb));
 return 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);
 Lunar<Account>::Register(L);
 if (argc>1) {
 printf("loading '%s'\n", argv[1]);
 if (report(L, luaL_loadfile(L, argv[1]) || lua_pcall(L, 0, 0, 0)) == 0) {
 printf("running application\n");
 if (report(L, lua_cpcall(L, &application, 0)) == 0) {
 printf("okay\n");
 }
 }
 }
 lua_setgcthreshold(L, 0); // collected garbage
 printf("close\n");
 lua_close(L);
 printf("done\n");
 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
function Account:show()
 printf("Account balance = $%0.02f\n", self:balance())
end
parent = {}
function parent:rob(amount)
 amount = amount or self:balance()
 self:withdraw(amount)
 return amount
end
getmetatable(Account).__index = parent
function main()
 print('a =', a)
 print('b =', b)
 print('metatable =', getmetatable(a))
 print('Account =', Account)
 table.foreach(Account, print)
 a:show() a:deposit(50.30) a:show() a:withdraw(25.10) a:show()
 debug.debug()
end

Test Code Output

$ ./test setup.lua
loading 'setup.lua'
running application
Account balance = 100ドル.00
Account balance = 30ドル.00
a = Account (0x22fcb0)
b = Account (0xa041d98)
metatable = table: 0xa044f28
Account = table: 0xa044f28
show function: 0xa0464a0
balance function: 0xa0455f8
withdraw function: 0xa045300
deposit function: 0xa045508
new function: 0xa044fe8
Account balance = 100ドル.00
Account balance = 150ドル.30
Account balance = 125ドル.20
lua_debug> a:show()
Account balance = 125ドル.20
lua_debug> b:show()
Account balance = 30ドル.00
lua_debug> b:deposit(0.01) b:show()
Account balance = 30ドル.01
lua_debug> c = Account(19.99) c:deposit(b:rob()) c:show()
Account balance = 50ドル.00
lua_debug> b:show()
Account balance = 0ドル.00
lua_debug> b = nil
lua_debug> print('c =', c)
c = Account (0xa048cf8)
lua_debug> cont
deleted Account (0x22fcb0)
okay
deleted Account (0xa041d98)
close
deleted Account (0xa048cf8)
done

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Last edited January 6, 2007 1:32 pm GMT (diff)