Re: Wrapping existing FILE *s as Lua file objects

[Mildred <ml.mildred593@...>]

Le sam 13/01/2007 à 00:50 Reuben Thomas à écrit:
> I can't see a way to do this after looking at liolib.c and googling a
> bit. It's obviously fairly trivial to extend liolib.c to do it, but a
> pain as you can't do it with vanilla Lua.
> 
> Am I missing something? I don't imagine it's that rare to want to
> pass a FILE * obtained from somewhere else into a Lua script without
> re-inventing the liolib wheel...
> 

I looked at it yesteday and it is simple.

A file object is just a full userdata that contains a pointer to the
FILE* object associated with the metatable that have the name
LUA_FILEHANDLE in the registery
(LUA_FILEHANDLE seems to be defined in lualib.h)

So I think it would look like:

FILE** ud = lua_newuserdata(L, sizeof(FILE*));
lua_getfield(L, LUA_REGISTERYINDEX, LUA_FILEHANDLE);
lua_setmetatable(L, -2);
*ud = my_file_object;

and to get it back (found in liolib.c):

FILE* f = *((FILE **)luaL_checkudata(L, 1, LUA_FILEHANDLE));

(source code not checked)

Mildred
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