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

[<qa...@ho...>]

Hi,

The type is signed, but as you can see there are no negative values=
 [0...11, 0...65536, 0...4], so that shouldn't be the problem because the=
 most significant bit is zero. I've tried every possible combination I can=
 think of but I can't not figure out where the extra bytes comes from.

/J=F6rgen

*********** REPLY SEPARATOR  ***********

On 2003-03-06 at 16:51 Per Westermark wrote:

>You don't show what type value has, but if it's signed, your in for a bit
>of surprise if you try and shift and mask on it.
>
>Most compilers - not all as Ioannis and I have had an earlier discussion
>about yesterday :-) - will shift in most significant bit set if you shift
>a negative value to the right.
>
>Note that 0xbd is the same is 189 unsigned or -67 signed.
>
>/Per W
>
>On Thu, 6 Mar 2003, "J=F6rgen" wrote:
>
>> Hi.
>>
>> This problem puzzles me. I have the following data.
>> -4 0 0 4 1 0 4 2 0 3 2 27 1 3 108 1 3 135 1 3 189 1 3 351 1 4 0 8 5 0 4
>6 0 4 7 0 4 8 0 4 9 0 3 9 27 1 10 27 2 10 36 1 10 54 1 11 108 1 11 189 1
>>
>> I'm not to familiar with reg.exp, but I guess that the reg.exp. for the
>data would be
>> result [value1 value2 value3]*
>>
>> where
>>   result is an integer but is always in the range -64 to 64
>>   value1 is an integer but is always in the range 0 to 11
>>   value2 is an integer but is always in the range 0 to 65536
>>   value3 is an integer but is always in the range 0 to 4
>>
>> let's say that we call [value1 value2 value3] for 'value' and
>'nbrOfValues' the number of sets of 'value'. In this case nbrOfvalues =3D=
 20
>>
>> When I write the data to file, using ofstream foo("foofile") I do it in
>the following way
>>
>> if(result < 0)
>>   foo << '-';
>> else
>>   foo << '+';
>> foo << ((unsigned char) (abs(result) & 0x000000FF));
>>
>> for(int i=3D0; i<numberOfValues; i++){
>>   foo << ((unsigned char) (value[i][0] & 0x000000FF));
>>   foo << ((unsigned char) ((value[i][1] & 0x0000FF00) >> 8));
>>   foo << ((unsigned char) (value[i][1] & 0x000000FF));
>>   foo << ((unsigned char) (value[i][2] & 0x000000FF));
>> }
>>
>> The problem comes when I read the data from file. If I just reverse the
>procedure and prints the decoded data to screen I get
>> -4 0 0 4 1 0 4 2 0 3 2 27 1 3 108 1 3 135 1 3 189 1 3 351 1 4 0 8 5 0 4
>6 0 4 7 0 4 8 0 4 9 0 3 9 27 1 10 27 2 10 36 1 10 54 1 11 108 1 11 189 1 0
>80 114
>>
>> It looks just the same as the original data except for the last three
>numbers (0 80 114).
>>
>> When looking at the filesize it shows that it is 85 bytes, but the data
>written is only 82 bytes
>>
>> For debugging purposes, instead of writing directly to file, I first
>store everything in a string s. That is, replacing foo << ... with s +=3D
>... Finally I write it to file with foo << s;
>>
>> When I print the string s to screen in hex-mode
>>
>> cout.setf( ios_base::hex, ios_base::basefield );
>> for(int i=3D0; i<s.size(); i++)
>>   cout << " " << s[i];
>>
>> it gives the following output
>> 2d 4 0 0 0 4 1 0 0 4 2 0 0 3 2 0 1b 1 3 0 6c 1 3 0 87 1 3 0 bd 1 3 1 5f
>1 4 0 0 8 5 0 0 4 6 0 0 4 7 0 0 4 8 0 0 4 9 0 0 3 9 0 1b 1 a 0 1b 2 a 0 24
>1 a 0 36 1 b 0 6c 1 b 0 bd 1
>> and it is the way it should be
>>
>> But when I look at the datafile in a hexeditor I see
>> 2d 4 0 0 0 4 1 0 0 4 2 0 0 3 2 0 1b 1 3 0 6c 1 3 0 87 1 3 0 bd 1 3 1 5f
>1 4 0 0 8 5 0 0 4 6 0 0 4 7 0 0 4 8 0 0 4 9 0 0 3 9 0 1b 1 d a 0 1b 2 d a
>0 24 1 d a 0 36 1 b 0 6c 1 b 0 bd 1
>>
>> An extra byte 'd' emerges before every one of the three "value1"-'a'
>bytes (d a 0 1b 2 , d a 0 24 1 , d a 0 36 1).
>>
>> Where did these 'd' bytes come from?
>> Why are the only occuring in front of the 'a' byte?
>> How come that when I print the data to screen it does not mess up the
>values but instead appends (0 80 114) at the end?
>> Finally, and most important, how do I get rid of them?
>>
>>
>> Any ideas are very welcome.
>>
>> TIA
>> /J=F6rgen
>>
>>