Re: how to communicate unsigned char* to Java

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Let me just make a summary of how to communicate unsigned char* from C++ to
Java, which enabled me to communicate the r, g, b values of a picture:

In Java I wrote the code:
int[] pix = new int[count]; //this array has the r, g, b values, count =
width*height
FileInputStream pixelFile = new FileInputStream("C:\\pixelvalues.dat");
DataInputStream pixelData = new DataInputStream(pixelFile);
byte[] pixelByte = new byte [3*count];
try
{
pixelData.read(pixelByte);
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
red = (int)pixelByte[y*pixelsw + x] & 0xff;
green = (int)pixelByte[count + y*pixelsw + x] & 0xff;
blue = (int)pixelByte[2*count + y*pixelsw + x] & 0xff;
pix[y*pixelsw + x] = 0xff000000 | ((red<<16) + (green<<8) + blue);
}
}
}
catch (IOException e)
{
}

and in C++ I wrote the code:
unsigned char *pixels = ... //the length of this array is 3*count
const char *charpixels = reinterpret_cast<char*>(pixels);
fstream file;
file.open("C:\\pixelvalues.dat", ios::out | ios::binary);
file.write(charpixels, 3*count);
file.close();

Thanks to everyone for participating in this discussion!


"Ali" wrote:

On May 24, 1:25 am, "Günter Prossliner" <g.prossliner/gmx/at> wrote:
Hello Ali!

Snip from GP:
This will not work, allthough it _may_ work on some bunch of data.

And what is the data limit of this working solution? i mean the max
size when this tech. will stop working.

It is not about size. It will stop working when a specific byte-sequences
occure within the binary data which are no valid Unicode.

When you use ANSI Strings to read binary data
1. every byte stands for it's own
2. every possible value has an opposite Character within ANSI

==> you may read any binary data as an ANSI String. "String" is just an
representation of the underlying binary data, so you can convert them
without loosing information. Allthough in languages which supports an
explicit binary type (in opposite to c++ which uses 'char' for character and
binary), this was never a good coding practice.

As opposite to Unicode:
1. characters are encoded in more than one byte (when using UTF-16)
2. NOT every possible combination of values is an valid Unicode
Code-Point.

What happens when an Unicode-Parser dedects an invalid byte-Sequence?
* Thrown an error (in this case you will not be able to read the data at
all)
* Substitute the invalid sequence to something want may be SIMILAR (an
in this case you will not get the same binary data when you interpret this
string a binary data).
* Skipp the invalid character (needless to say that you will loose data)

Just check out the UNICODE specification for details.

see:http://www.unicode.org/reports/tr22/(a document specifing an
XML-format for UNICODE Exchange).

======================================================
1.1 Illegal and Unassigned Codes

00 The sequence is illegal. There are two variants of this.
First is where the sequence is incomplete. For example,

* 0xA3 is incomplete in CP950.
Unless followed by another byte of the right form, it is illegal.

* 0xD800 is incomplete in Unicode.
Unless followed by another value of the right form, it is illegal.

* 0xDC00 is incomplete in Unicode.
Unless preceded by another value of the right form, it is illegal.

The second variant is where the sequence is complete, but explicitly
illegal. For example,
0xFFFF is illegal in Unicode. This value can never occur in valid Unicode
text, and will never be assigned.

00 The source sequence represents a valid code point, but is unassigned (aka
undefined). This sequence may be given an assignment in some future
(evolved) version of the character encoding
.
For example,
* 0xA3 0xBF is unassigned in CP950, as of 1999.
* 0x0EDE is unassigned in Unicode, V3.0

00 The source sequence is assigned, but unmappable: there is no
corresponding code point in the target encoding to accurately represent the
source sequence.
For example,

The long dash is assigned in Unicode, but cannot be mapped to ISO-8859-1.

In the case of illegal source sequences, a conversion routine will typically
provide the following options:

* stop (or throw an exception)
in particular, stopping is commonly used by higher level character encoding
schemes, such as ISO 2022 conversions, to know when to stop converting into
one encoding and pick another to convert to.
in either case, the information as to length of the bad sequence should be
available and the conversion should be resumable (after the caller handles
the bad sequence).

* skip the source sequence
while this is commonly an option, it can also hide corruption problems in
the source text.

* map to a substitution character
such as the Unicode U+FFFD REPLACEMENT CHARACTER.
======================================================

see:http://unicode.org/faq/utf_bom.html#40
======================================================
Q: Are there any 16-bit values that are invalid?

A: The two values FFFE16 and FFFF16 as well as the 32 values from FDD016 to
FDEF16 represent noncharacters. They are invalid in interchange, but may be
freely used internal to an implementation. Unpaired surrogates are invalid
as well, i.e. any value in the range D80016 to DBFF16 not followed by a
value in the range DC0016 to DFFF16, or any value in the range DC0016 to
DFFF16 not preceded by a value in the range D80016 to DBFF16. [AF]

======================================================

GP

GP! thanks for value thoughts and i enjoyed reading that. Well, i
guess it seems another discussion like OO verses structural
programming or good programming verses bad one;-)

ali



.

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