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

Sorry for looseness in terminology, but you always send bytes. The
interpretation of the data (as a string or as a double) is up to you and
your code.

Mike

"Ananya" <Ananya@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:AA6F501C-7A17-4D06-8435-ACF3A401E8DB@xxxxxxxxxxxxxxxx
How can I send the string as string (not bytes) in Java and how can I
receive
it in C++?


"Ananya" wrote:

Ok, but Michael suggested to send a string for getting around the bytes
endian problem.

So I don't want to send a string as bytes. Can I send a string as a
string?


"Scherbina Vladimir" wrote:

If I recall correctly you can convert "string" data type on Java side
to a
bytes array using .getBytes(...) or something like that.

--
--Vladimir, Windows SDK MVP
"Ananya" <Ananya@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:21045337-B7CE-4FC2-86B0-4631DCBFF7D1@xxxxxxxxxxxxxxxx
That sounds great! But can I actually send and receive strings? I
thought
that I only can send and receive bytes. How do I send and receive
strings?

Thanks in advance for your answer!


"Michael K. O'Neill" wrote:

You can eliminate all issues of endian-ness by converting the
doubles to
strings (sprintf-style) and sending the string. On the receiving
side,
use
an atof() function to convert back.

Note that this approach also resolves all issues concerning whether
the
sending and receiving side are both using the same implementation
of
IEEE-754 for storing double precision numbers. Since string
equivalents
are
sent, the precise implementation simply doesn't matter.

Finally, it's often easier to debug, since you can "see" the number
that's
being sent.

Mike

"Scherbina Vladimir" <v_scherbina@xxxxxxxxxxxxxxx> wrote in message
news:EB69C218-6DAE-4776-ABC0-F601C7878116@xxxxxxxxxxxxxxxx
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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