Re: binary data as string snag
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- Subject: Re: binary data as string snag
- From: Edgar Toernig <froese@...>
- Date: 2001年2月07日 03:27:37 +0100
Hi,
John Belmonte wrote:
> I started implementing Perl-style pack/unpack functions using Lua strings for
> binary data but ran into a snag. Using strings is fine if you're just looking
> to write data out to a file.
> However if you want to pass the strings to C to be used directly then there are
> alignment issues.
You could try to stuff padding bytes at the head of the string (number of bytes
detected during libsetup). But I would simply copy it like that:
struct bar {...};
extern void foo(struct bar *);
static int
call_foo(lua_State *L)
{
struct bar tmp;
foo(arg_check_struct(L, 1, &tmp, sizeof(tmp)));
return 0;
}
static void *
arg_check_struct(lua_State *L, int argno, void *buf, size_t len)
{
size_t l;
char *str = luaL_check_lstr(L, argno, &l);
luaL_arg_check(L, l == len, argno, "invalid structure size");
memcpy(buf, str, l);
return buf;
}
Compared to the creation of the packed strings the time to copy it once more
should be negligible. Only 'P' will not work that way. The last resort
would be a userdata...
Ciao, ET.