Re: socket communication: send & receive doesn't work right
- From: "Scherbina Vladimir" <v_scherbina@xxxxxxxxxxxxxxx>
- Date: Sat, 28 Apr 2007 16:34:41 +0300
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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