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Lua Callbacks in C

Started by HyperHacker Nov 23, 2009 at 10:47 PM 2 replies 3.4k views

Original Post

Nov 23, 2009 at 10:47 PM

I'm writing a program that uses Lua, and I've hit a snag. I want to pass a Lua function to a C function as a callback. Like: someCFunction(function(foo) print(foo) end) Then at some point the script calls another C function, which calls the callback passed above. However I don't see a way to retrieve functions passed as parameters in C. I can call it when it's still on the stack, but I need to retrieve it and store it to call later. Is this possible?

Ximmer

Nov 24, 2009 at 12:44 AM

I think you have 2 options,

#1 Pass the name of the function and store that for a later:

lua_pushstring(L, callback_function_name);
lua_getglobal(L, -1);

#2 Save the function on the stack to a temporary unique global and save the name of that global in your event or what have you

ddn3

Nov 24, 2009 at 5:09 PM

This page should help. Bascialy it's like what Ximmer suggested, but since this situation occurs so often, Lua has a built in functionality to address it.

http://www.lua.org/pil/27.3.1.html
http://bigbucketsoftware.com/2006/03/15/lua-and-the-registry/

Lua has a registry table for storing away Lua side objects which can then be referenced again from the Lua side using just a key.

-ddn

HyperHacker

Nov 26, 2009 at 12:43 AM

Thanks, that looks like it'll do.

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