UDP Socket communication using different ports between two hosts - sockets

Question

I have a device that listen to UDP packets on port IN_PORT and echo the message on port OUT_PORT. I can communicate with it using a test software like Packet Sender.
I have to write a C++ library (Win32 at the moment) to communicate with the device. I made several tests but I still wasn't able to communicate. My guess is to use this workflow:
create socket
fill sockaddr_in structure with the device address, AF_INET family and the listeng port (OUT_PORT)
bind the socket
change sockaddr_in.sin_port with IN_PORT and send a packet (using sendto)
wait for an answer (using recvfrom)
repeat from 4
This works if I simulate the device with the Packet Sender utility working locally (device address = 127.0.0.1). I can't use the same workflow to connect to a remote address, even in the same subnet (e.g. my PC address: 192.168.1.2, remote PC address 192.168.1.5), since I get WSAEADDRNOTAVAIL error.
I've tested several different workflows, and read several discussions on the topic here and there, but none works, awfully.
Can someone give me some hints on the subject.
Thanks!
MIX

Answer 1

Your work flow is slightly wrong. It should be more like this instead:
create socket
fill sockaddr_in structure with the address of the local network adapter that is communicating with the device, AF_INET family, and the listenig port (OUT_PORT)
bind the socket
change sockaddr.sin_addr with device address, and sockaddr_in.sin_port with IN_PORT, and send a packet (using sendto)
wait for an answer (using recvfrom)
repeat from 4

Answer 2

I changed my code following Remy Lebeau hints. It works now. If someone will like to have a look and spot some weak points, or suggest improvements, I'll be glad (a code that "just works" is never enough; it must also "shine"!). Comments mark the previous (wrong) version of the code.
#pragma comment (lib, "Ws2_32.lib")
#include <winsock2.h>
#include <stdlib.h>
#include <stdio.h>
#include <STRING>
#define IN_PORT 18
#define OUT_PORT 17
#define LOCAL_IP "10.0.10.108"
#define DEVICE_IP "10.0.10.104"
#define DEFAULT_BUFLEN 1024
int main(int argc, char *argv[])
{
WSADATA wsaData;
SOCKET sck;
struct sockaddr_in sckAddrInfo;
bool terminate;
char dataBuffer[DEFAULT_BUFLEN];
int rcvDataLength;
int sckAddrInfoLength;
WSAStartup(MAKEWORD(2,2), &wsaData);
sck = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
memset((&sckAddrInfo), 0, sizeof(sckAddrInfo));
sckAddrInfo.sin_family = AF_INET;
sckAddrInfo.sin_port = htons(IN_PORT);
//sckAddrInfo.sin_addr.s_addr = inet_addr(DEVICE_IP); // WRONG! Must bind local address
sckAddrInfo.sin_addr.s_addr = inet_addr(LOCAL_IP);
bind(sck, (struct sockaddr*)(&sckAddrInfo), sizeof(sckAddrInfo));
terminate = false;
sckAddrInfoLength = sizeof(sckAddrInfo);
while(!terminate)
{
printf("Write echo request: ");
gets(dataBuffer);
sckAddrInfo.sin_addr.s_addr = inet_addr(DEVICE_IP); // Must set device address, too, not just output port
sckAddrInfo.sin_port = htons(OUT_PORT);
sendto(sck, dataBuffer, strlen(dataBuffer), 0, (struct sockaddr*)(&sckAddrInfo), sizeof(sckAddrInfo));
memset(dataBuffer, '\0', DEFAULT_BUFLEN);
rcvDataLength = recvfrom(sck, dataBuffer, DEFAULT_BUFLEN, 0, (struct sockaddr*)(&sckAddrInfo), &sckAddrInfoLength);
printf("Device answer: %s\n", dataBuffer);
if(strcmp(dataBuffer, "quit") == 0)
terminate = true;
}
closesocket(sck);
WSACleanup();
return 0;
}