hi. i''m using c# and is trying to use lua with it. the base is rather simple with some [DllImport("lua.dll")] UIntPtr lua_open(); etc. but i have run in to a problem. see, lua_register() is a define of 3 statements: lua_pushstring() - pushes the function name into the stack lua_pushcclosure() - pushes the function into the stacl lua_settable() - "sets" the function and lua_pushcclosure() needs a function pointer. but how do i get that function pointer in c# ?! i''ve tried using delegate but when and it runs fine, but it crashes just after i''ve run the function with a System.NullReferenceException: System.NullReferenceException: Object reference not set to an instance of an object. any idea why ?

A delegate is what you should marshall from C# into unmanaged code when a function pointer is expected. Maybe you could give us some more details?


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Yeah, we need some code :/

oh, sorry. here's what i've done:

LUA.cs

namespace Scripting{	class LUA	{		// The delegate for the Register() function		public delegate int lua_CFunction(UIntPtr L);				// Private LUA functions (liblualib.dll = lua.dll)		[DllImport("liblualib.dll")] private static extern UIntPtr lua_open();		[DllImport("liblualib.dll")] private static extern void lua_close(UIntPtr L);		[DllImport("liblualib.dll")] private static extern int lua_dofile(UIntPtr L, string filename);		[DllImport("liblualib.dll")] private static extern void lua_pushstring(UIntPtr L, string s);		[DllImport("liblualib.dll")] private static extern void lua_settable(UIntPtr L, int idx);		[DllImport("liblualib.dll")] private static extern void lua_pushcclosure(UIntPtr L, lua_CFunction fn, int n);...		// Private LUA constants		private const int LUA_GLOBALSINDEX = -10001;...		// Public functions		public int DoFile(string filename)		{			return lua_dofile(L, filename);		}		public void Register(string n, lua_CFunction f)		{			lua_pushstring(L, n);			lua_pushcclosure(L, f, 0); // lua_pushcfunction(L, f)			lua_settable(L, LUA_GLOBALSINDEX);		}		.		.		.	}}

MainForm.cs

namespace MyNamespace{	class MainForm	{		.		.		.		private void Test_Click(object sender, EventArgs e)		{			LUA L = new LUA();			L.Register("Test", new LUA.lua_CFunction(l_Test));			if( L.DoFile("test.lua") != 0 )				MessageBox.Show(L.ToString(0));					// Debugging			System.Windows.Forms.MessageBox.Show(L.ToString(L.GetGlobal("testvar")));		}...		public static int l_Test(UIntPtr L)		{			LUA.PushString(L, "Testing");			return 1;		} // <- crashes after here (i guess)...	}}

test.lua

testvar = Test();

[edited by - arthc on July 21, 2003 4:55:36 AM]

Do you have symbols and source for the Lua stuff? If so, you can step into the Lua code in order to see where it crashes and/or get a better stack trace. Note that you have to enable debugging of native code in this case, and debugging will be veerrry slow.

BTW: Where does the L come from in the LUA class? Does it get initialized?


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hmm.. i tried stepping through the code but it doesn't get "inside" so i can't debug. dunno why.

L is an UIntPtr and gets initialized in the LUA() constructor simply with L = lua_open();

my guess is that the dll loses its instance when a new instance of the LUA class is created. i'll try making them static or something

EDIT: Doh. they are already static..

[edited by - arthc on July 21, 2003 7:16:10 PM]

quote: Original post by arthc
hmm.. i tried stepping through the code but it doesn''t get "inside" so i can''t debug. dunno why.

Well, as I mentioned, you need the debug symbols(*.pdb) for the Lua source, as well as the source itself.

i do have the source and the symbols. still i can''t step through the code.

Did you enable native debugging? Properties->Configuration Properties->Debugging->Debuggers->Enable Unmanaged Debugging. But I warn you - its slooooowww...

Also, the Modules(Debugger->Windows->Modules) window will tell you if the debugger was able to load symbols.