Sending Struct over UDP

I want to send a STRUCT over UDP using CAsyncSocket, based on a demo class I found called CUdpAsySk. Sending strings work nicely. Then creating a struct:

//struct defined in CUdpAsySk.h
struct StoSend
{
int16 version;
double gps_lat;
double gps_long;
}
class CUdpAsySk : public CAsyncSocket
{
public:
StoSend*pStoSend;
StoSend*pStoReceive;
...

}
//Send struct in void CUdpAsySk::DoAsyncSendBuff()
m_strRemote="192.168.1.5";
m_nPort=4000;
dwBytes = SendTo((const char *)&pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote);


//Receive
nRead = ReceiveFrom((char *)&pStoReceive, 699999, m_strRemote, m_nPort);

This work on local computer when bytes sent are equal or less then 20 bytes, from a remote computer no struct is received. When is failes I receive a:
Unhandled exception at 0x7c1772af (mfc71d.dll) in Device.exe: 0xC0000005: Access violation reading location 0x00000f94.

Anyone here that can help me with this problem?

Break into the debugger, and see where you are in the stack. There is not enough code provided to say. Also, please use code tags when posting code.

Viggy

Well just looking at your send command, you are sending a reference to a pointer. Should be:

Code:

---

dwBytes = SendTo((const char *)pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote);

---

Quote:

---

Originally Posted by [email protected]

dwBytes = SendTo((const char *)&pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote);


//Receive
nRead = ReceiveFrom((char *)&pStoReceive, 699999, m_strRemote, m_nPort);

Anyone here that can help me with this problem?

---

Do I need to convert the struct into bytes before sending it or is this the correct way of sending a struct over UDP?

Its fine.

Is your server echoing the bytes back?
nRead = ReceiveFrom((char *)&pStoReceive, sizeof(StoSend), m_strRemote, m_nPort);

dwBytes = SendTo((const char *)&pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote);

nRead = ReceiveFrom((char *)&pStoReceive, sizeof(StoSend), m_strRemote, m_nPort);

Sending a struct of 24 bytes local the pStoReceive is received correctly, however sending more then 24 bytes I get a error msg: Unhandled exception at 0x7c1772af (mfc71d.dll) in Device.exe: 0xC0000005: Access violation reading location 0x00000f94.

using: LAN PC to PC no data is transmitted correctly?

using: dwBytes = SendTo((const char *)pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote); no data is transmitted correctly?

If you are going to send an array you are going to have to multiply and reflect that in your sendto and recvfrom.

sizeof(StoSend) * nArrayElements

Finally found the correct way, the problem is unneeded casting and incorrect handling of pointers :)

dwBytes = SendTo(pStoSend, sizeof(*pStoSend), m_nPort,m_strRemote);

nRead = ReceiveFrom(pStoReceive, sizeof(*pStoReceive), m_strRemote, m_nPort);

Well you really shouldn't use sizeof on a dereferenced pointer, you should use sizeof on a type.

Hence:

Code:

---

dwBytes = SendTo(pStoSend, sizeof(StoSend), m_nPort,m_strRemote);

nRead = ReceiveFrom(pStoReceive, sizeof(StoReceive), m_strRemote, m_nPort);

---