Re: socket communication: send & receive doesn't work right

In Windows everything is little endian, http://support.microsoft.com/kb/q102025/. I suggest you to send simple data from java program, and analyze what you obtain on c++ side. For example, send an integer value 10, and tell us here what you recieve in C++ application.

--
--Vladimir, Windows SDK MVP
"Ananya" <Ananya@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:7E0E8354-A53A-4B8F-A0B4-33A51785FEE4@xxxxxxxxxxxxxxxx
Well, I tried not to reverse bytes by saying:
for (i = 0; i < j; i++)
{
ptr[i] = result[i];
}

instead of:
for (i = 0; i < num; i++)
{
for (j=0; j<sizeof(double); j++)
{
ptr[i*sizeof(double)+j] = (char)result[(i+1)*sizeof(double)-j-1];
}
}
in my C++ receiving method.

But now the doubles:
1.23 & 4.5
which I send from my Java program always become:
1.8584604523406555e+038 & 5.910042899492e-318#DEN
in my C++ program.

Please help! By the way, how can I test if my server needs reversing bytes
or not?

"Scherbina Vladimir" wrote:

I am saying that if your server is big endian, then you _do_not_ need to
reverse bytes.

--
--Vladimir, Windows SDK MVP
"Ananya" <Ananya@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:8B29C2D6-060A-41BA-8180-F4AA146F49A6@xxxxxxxxxxxxxxxx
> Thanks! Are you saying that in my C++ receiving method the code for
> reversing the byte order is incorrect? Where can I find the correct > code?
>
>
> "Scherbina Vladimir" wrote:
>
>> The problem with this approach is that Java stores the binary data as >> big
>> endians only (no matter what CPU architecture is), if your C++ client >> is
>> litttle endian then unpredictable results may be obtained. Check this
>> issue.
>>
>> -- >> --Vladimir, Windows SDK MVP
>> "Ananya" <Ananya@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
>> news:2951DED5-4DDF-40BF-A581-1A13A95EA631@xxxxxxxxxxxxxxxx
>> >I am trying to establish socket communication between my Java and C++
>> >program.
>> >
>> > I called my Java program from my C++ program with ShellExecuteEx.
>> > I created a C++ Server and a Java Client, which is accepted by the
>> > Server.
>> >
>> > I did a test of sending two doubles:
>> > 1.23 & 4.5
>> > from my Java program to my C++ program, however I always received >> > the
>> > following 2 different doubles:
>> > 1.1648250968930678e-302 & -6.4627233651951511e-086.
>> >
>> > Here is my Java sending method:
>> > public void send_doubles(double vals[], int len) throws IOException
>> > {
>> > // convert our array of doubles into an array of bytes
>> > ByteArrayOutputStream bytestream;
>> > bytestream = new ByteArrayOutputStream(len*8);
>> >
>> > DataOutputStream out;
>> > out = new DataOutputStream(bytestream);
>> >
>> > for (int i=0; i<len; i++)
>> > {
>> > out.writeDouble(vals[i]);
>> > }
>> >
>> > output.write(bytestream.toByteArray(), 0, bytestream.size());
>> > output.flush();
>> >
>> > recv_ack();
>> > send_ack();
>> > }
>> >
>> > and my Java acknowledgement methods:
>> > // send a short acknowledgement to the server
>> > private void send_ack() throws IOException
>> > {
>> > int ack;
>> >
>> > ack = 0;
>> >
>> > output.write(ack);
>> > output.flush();
>> > }
>> >
>> > // recv a short acknowledgment from the server
>> > private void recv_ack() throws IOException
>> > {
>> > int ack;
>> >
>> > ack = (int)input.read();
>> > }
>> >
>> > And here is my C++ receiving method:
>> > int Server::recv_doubles(double *val, int maxlen) throw (string)
>> > {
>> > int i, j;
>> > int numbytes = 0;
>> > int end = 0;
>> > int total_bytes = 0;
>> > char *temp;
>> > char *result;
>> >
>> > temp = (char *)buffer;
>> > result = (char *)buffer2;
>> >
>> > j = 0;
>> >
>> > // we are receiving the incoming doubles one byte at a time
>> > while (!end)
>> > {
>> > if ((numbytes=recv(new_fd, temp, BUFFSIZE, 0))==-1)
>> > {
>> > throw string("help!");
>> > }
>> >
>> > for (i=0; i<numbytes; i++)
>> > {
>> > result[j] = temp[i];
>> > j++;
>> > }
>> >
>> > total_bytes = total_bytes + numbytes;
>> > if (total_bytes==maxlen*sizeof(double) + 1)
>> > {
>> > end = 1;
>> > }
>> > }
>> >
>> > // now we need to put the array of bytes into the array of doubles
>> > char *ptr;
>> > int num = (j - 1)/sizeof(double);
>> >
>> > ptr = (char *)val;
>> >
>> > // going from Java to C++, we need to reverse the order of each set >> > of
>> > bytes
>> > for (i = 0; i < num; i++)
>> > {
>> > for (j=0; j<sizeof(double); j++)
>> > {
>> > ptr[i*sizeof(double)+j] = (char)result[(i+1)*sizeof(double)-j-1];
>> > }
>> > }
>> >
>> > send_ack();
>> > recv_ack();
>> >
>> > return num;
>> > }
>> >
>> > and my C++ acknowledgement methods:
>> > // receive a short acknowledgement from the client
>> > void Server::recv_ack()
>> > {
>> > char temp[1];
>> > int total = 0;
>> >
>> > while (total<1)
>> > {
>> > total += recv(new_fd, temp, 1, 0);
>> > }
>> > }
>> >
>> > // send a short acknowledgement to the client
>> > void Server::send_ack()
>> > {
>> > char temp[1];
>> > temp[0] = 42;
>> >
>> > send(new_fd, temp, 1, 0);
>> > }
>> >
>> > Why does my C++ program receive incorrect doubles?
>> >
>> > Thanks for looking at my code!
>> >
>> >
>>


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