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Data loss in Type Conversion.

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Join Date: Sep 2004

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Layla_2401 Layla_2401 is offline

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Data loss in Type Conversion.

Sep 25th, 2004

Hello Everyone,

I'm working on a couple of programs, client/server. I'm using winsock library to handle data transfer between the two programs. I'm having a problem when it comes to sending int values, they must be converted to (char *) since that's the data type of the buffers used in the socket Send() and Recv() functions. to elaborate, consider the following:

Client side:
-----------
unsigned char rnd[4];
int noncer =0;

// Generating a random number
RAND_pseudo_bytes(rnd,sizeof(rnd));

noncer = (int)rnd;

non1=(char*)noncer;

// These two lines produce the same output which is 1244556
cout <<"\n Noncer :" << noncer << "\n";
cout.flush();
cout <<"\n Noncer char :" << (int)non1 << "\n";
cout.flush();

SendData(Socket, non1);

Server Side:
-----------
int client_nonce;
char String[50];
String_initialization(String);

// Reading the nonce identifier
RecieveMessage(socket, String, number_of_bytes);
client_nonce = (int)String;

// this results in 1244588 !!
cout<<"\n the nonce is:"<<client_nonce <<endl;
cout.flush();

If anyone can tell me what's causing the change of data i'd really appreciate it.

Thank you all in advance.
Layla.

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Join Date: Sep 2004

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Narue

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Re: Data loss in Type Conversion.

Sep 25th, 2004

Don't play around with casting like that unless you know what you're doing. Type punning can be tricky business, but barring transmission issues with your sockets, this should work:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <cstring>
#include <iostream>
 
using namespace std;
 
int main()
{
  int i1 = 12345;
  char buffer[sizeof ( int )];
 
  memcpy ( buffer, (unsigned char *)&i1, sizeof ( int ) ); // Simulate send/recv
 
  int *pi = (int *)buffer;
  cout<< *pi <<endl;
}
#include <cstring>
#include <iostream>

using namespace std;

int main()
{
  int i1 = 12345;
  char buffer[sizeof ( int )];

  memcpy ( buffer, (unsigned char *)&i1, sizeof ( int ) ); // Simulate send/recv

  int *pi = (int *)buffer;
  cout<< *pi <<endl;
}

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Join Date: Sep 2004

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Layla_2401 Layla_2401 is offline

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Re: Data loss in Type Conversion.

Sep 25th, 2004

Hi Narue,

Thank you SO much for your help, I now get the same value at both sides

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Join Date: Mar 2006

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dimkovtrajce dimkovtrajce is offline

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Re: Data loss in Type Conversion.

Mar 22nd, 2006

Hi I am having the same problem, but I couldnt solve it.
I need to send a CString with Unicode (16bit) to the send and recv function. Unfortunately all i get is garbage

Any help is welcomed