LuaJIT, how to convert cdata to userdata?

Question

I want to use LuaJIT for its ability to create structs and arrays in Lua. But my functions which use the data require userdata or a string (not a string representation, just used as a container) that stores the data.

But looking through the api I don't see if this is even possible. Is it?

Thanks.

see my answer [here](http://stackoverflow.com/a/30185945/1436359) — rraallvv, May 12 '15 at 08:48

score 3 · Accepted Answer · answered Sep 16 '13 at 07:40

3

LuaJIT FFI should not be mixed with classic C/API. While there are mechanisms to convert a const char* pointer to Lua string (ffi.string), there is no way to convert an FFI struct to Lua userdata.

FFI functions have no knowledge of a lua_State, which is needed to create userdata on the C side.

I don't know how large your C/API binding base is at the moment, but one solution would be to rewrite your C/API functions to FFI, if you're set on using FFI. You can do it gradually, making sure that there is a clear line between FFI and C/API.

answered Sep 16 '13 at 07:40

W.B.

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Thanks, but I prefer to use the c api in this case. I'll probably just make my own cstruct/carray generator for lua. – joesmoe891 Sep 16 '13 at 08:28
You sure? FFI is faster than the C API when compiled, and calls to C API functions cannot be compiled. – Colonel Thirty Two Sep 16 '13 at 14:11
Well speed isn't really an issue and I find the code organisation simpler this way. – joesmoe891 Sep 16 '13 at 15:37
I just wanted to add I ended up going with the ffi.string suggestion, I don't know what I was thinking before, but that was exactly what I needed. – joesmoe891 Nov 15 '13 at 17:15

LuaJIT, how to convert cdata to userdata?

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