Re: luajit string to char * conversion
- From: Konstantin Olkhovskiy <lupus@xxxxxxxxxx>
- To: luajit <luajit@xxxxxxxxxxxxx>
- Date: Wed, 19 Nov 2014 13:30:18 +0400
2014-11-19 11:50 GMT+03:00 marcelo nicolet <marcelo.nicolet@xxxxxxxxx>:
> Thank you, but the text you kindly pointed me to, reads like basic
> chinese to me. Not a single simple example...
>
Some examples can be found on the tutorial page [1].
> I must to think that cdata is some C native tipe data piece, and ct is
> some C data type. So, read in that way, it seems redundant. Also "pointers
> to addresses": roughly, what's the difference?
>
`cdata` can be described as a piece of lightuserdata, with underlying
stored C type known to the LuaJIT FFI.
If you call `type` on it, it should say "cdata". `ctype` is a type of
cdata, say "const char *", while cdata object
itself would hold an concrete instance of a pointer to character buffer.
`ffi.cast` is an analog of C cast. You
can cast a cdata of ctype "void *" to ctype "char *" (and you will get a
new cdata of new type, with same
pointer inside).
You can retrieve ctype using ffi.typeof. You can also cast Lua string to
"char *", but this will result in a cdata
pointer to LuaJIT internal memory buffer, so any modifications would result
in undefined behavior.
I still strongly recommend to read all the pages under "FFI Library", you
can avoid some basic mistakes. Bugs
in Lua software with heavy FFI usage are quite hard to debug.
[1] http://luajit.org/ext_ffi_tutorial.html
> --
Regards,
Konstantin
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