Re: opening a file in binary mode

[Edgar Toernig <froese@...>]

> >In any case, how do I open a file in binary and write binary data to it?
> >(I don''t want my numbers converted to strings, as that's what seems to
> >be happening)

And in what flavor do you want your numbers written?  Bytes?  Words?  Long
words?  Floats?  Doubles?  In what endian (little/big) or format (ieee floats,
BCD, ...).  It's really not that easy.  Standard Lua only supports simple
bytes via strchar() or format("%c").

> For numbers with fractional part, it's harder, but you may get by
> by using frexp. You might prefer to write a simple library that does this for
> you. Something like this (untested!):
> 
> static tobinary(lua_State* L)
> {
>  if arg is number then
>   void* u=lua_newuserdata(L,sizeof(double));
>   double x=lua_tonumber(L,1));
>   memcpy(u,&x,sizeof(x));
>  else if arg is string
>   ; /* do nothing */
>  return 1;
> }
> 
> and export this to Lua. Then you'd simply do write(tobinary(x)) in Lua.

Didn't test this myself but how should `write' know how to emit userdata???
Maybe you meant something like this (untested too ;-):

static tobinary(lua_State* L)
{
 double x = luaL_check_number(L, 1);
 lua_pushlstring(L, (const char *)&x, sizeof(x));
 return 1;
}

This converts a number to a binary string that holds the number in the
host's double representation.

Ciao, ET.