Re: [Dev-C++] Some extra bytes written to file?

[Ioannis V. <no...@ho...>]

-------Original Message-------=0D
 =0D
From: "J=F6rgen"=0D
Date: =D0=E1=F1=E1=F3=EA=E5=F5=DE, 7 =CC=DC=F1=F4=E9=EF=F2 2003 12:59:43 =
=F0=EC=0D
To: Ioannis Vranos; dev...@li...=0D
Subject: Re: [Dev-C++] Some extra bytes written to file?=0D
 =0D
See comments...=0D
 =0D
 =0D
[comment] =0D
What I'm trying to do is to reduce the size of the written file. Casting =
to
unsigned long gives=0D
me no reduction in size.=0D
E.g. =0D
  4 * char  =3D 4 * 8 =3D 32 bits =3D 4 bytes. =0D
  4 * unsigned long =3D 4 * 32 =3D 128 bits =3D 32 bytes=0D
 =0D
 =0D
 =0D
=3D=3D> At first as i said you apply casting wrong. =0D
=0D
=3D=3D> For example you wrote:=0D
=0D
foo << ((unsigned char) (value[i][0] & 0x000000FF)); =0D
=0D
=0D
=3D=3D> But it should be:=0D
=0D
foo << (unsigned char) (value[i][0]) & 0x000000FF; =0D
=0D
or better:=0D
=0D
foo << static_cast<unsigned char> (value[i][0]) & 0x000000FF; =0D
=0D
=0D
=3D=3D> or better you should have used bitset<unsigned whatever> from the
beginning.=0D
=0D
=0D
=3D=3D> After that, you are do these bitwise things to reduce the size? =0D
 =0D
=3D=3D> Keep in mind that for size reduction, binary file mode is better =
(but
with the cost of non=0D
file portability).=0D
 =0D
 =0D
[comment]=0D
 =0D
First. There are no negative integers (int) in the data so the problem
shouldn't be happening.=0D
Second. Lets say that the value of the int to be casted is 130. In bits i=
t
is written=0D
00000000 00000000 00000000 10000010=0D
Then it is masket with =0D
00000000 00000000 00000000 11111111=0D
and the result is=0D
00000000 00000000 00000000 10000010=0D
Now it is casted to unsigned char and we got the following bits=0D
10000010=0D
The value is still 130. If it were a signed char the bitrepresentation wo=
uld
still be=0D
10000010=0D
but the value would be -126=0D
 =0D
 =0D
=3D=3D> You can assume nothing about the implementation. You can assume a=
fter
the casting=0D
which you did wrong. Also for values larger than numeric_limits<unsigned
char>::max() you=0D
get data truncation.=0D
=0D
=0D
=0D
 =0D
 =0D
Ioannis Vranos=0D
 =0D
* Programming pages: http://www.noicys.freeurl.com=0D
* Alternative URL: http://run.to/noicys=20