// My First Internet Application
// By Matthew Cudmore, 2005
 
#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h> // For gethostname
 
#define MYPORT 4689
#define QUEMAX 10
#define BUFFER_LEN 100
 
#ifndef SOCKET_ERROR
#define SOCKET_ERROR -1
#endif
using namespace::std;
 
int main(void) 
{
	int sockfd, new_fd, sin_size;
	int sl = sizeof(struct sockaddr);
	struct sockaddr_in my_addr; // my address information
	struct sockaddr_in their_addr; // connector's address information
 
	// SOCK_STREAM or SOCK_DGRAM
	if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == SOCKET_ERROR )
	{
		// ERROR
		cout << "\n-- SOCKET error\n";
		return 0;
	}
 
	my_addr.sin_family = AF_INET;		// host byte order
	their_addr.sin_family = AF_INET;
 
	// Choose one method:
	// 1) my_addr.sin_port = htons(MYPORT); // short, network byte order
	// 2) my_addr.sin_port = htons(0);	// choose an unused port at random
	my_addr.sin_port = htons(MYPORT);	// short, network byte order
	their_addr.sin_port = htons(MYPORT);
 
	// Choose one method:
	// 1) my_addr.sin_addr.s_addr = inet_addr("10.12.110.57"); 
	// 2) inet_aton("10.12.110.57", &(my_addr.sin_addr));
	// 3) my_addr.sin_addr.s_addr = htonl(INADDR_ANY); // use my IP address
	my_addr.sin_addr.s_addr = htonl(INADDR_ANY); // use my IP address
 
	memset(&(my_addr.sin_zero), '\0', 8);	// zero the rest of the struct
 
	if (bind(sockfd, (struct sockaddr *)&my_addr,sizeof(struct sockaddr)) ==  SOCKET_ERROR) 
	{
		// ERROR
		cout << "\n-- BIND error\n";
		return 0;
	}
 
	// ###################################################################
 
	char Buffer[BUFFER_LEN];
	int BtsMvd;
 
	cout << "Simple sockets by Matthew Cudmore...\n";
	cout << "Your IP: " << inet_ntoa(my_addr.sin_addr) << "\n";
 
GetChoice:
		cout << "\nEnter choice action (x = exit, s = send, a = accept): ";
		cin.getline(Buffer, 99);
 
		if (Buffer[0] == 'x') 
		{
			closesocket(sockfd);
			return 0;
		}
		else if (Buffer[0] == 's') 
		{
			cout << "Enter the IP of the receiving machine: ";
			cin.getline(Buffer, 99);
			their_addr.sin_addr.s_addr = inet_addr(Buffer);
			memset(&(their_addr.sin_zero), '\0', 8);
			cout << "Enter a message to send to the receiving machine: ";
			cin.getline(Buffer, 99);
			if ((BtsMvd = sendto(sockfd, Buffer, sizeof(Buffer), 0,(struct sockaddr *)&their_addr, sizeof(struct sockaddr))) != -1)
			{
				cout << "\nMessage sent. Awaiting reply...";
			}
			else
			{
				cout << "\nMessage could not be sent.";
				goto GetChoice;
			}
			while (1) 
			{
				if ((BtsMvd = recvfrom(sockfd, Buffer, sizeof(Buffer), 0,(struct sockaddr *)&their_addr, &sl)) == -1) 
				{
						// ERROR
						cout << "\n-- recvfrom error\n";
						return 0;
				}
				if ( BtsMvd ) 
				{
					BtsMvd = strlen(Buffer);
					if (Buffer[ BtsMvd - 1 ] == '*') 
					{
						cout << "\nReturn received.";
						break;
					} 
					else
					{
						cout << Buffer<<" \nReturn-request ignored.";
					}
				}
			}
		}
		else if (Buffer[0] == 'a') 
		{
			cout << "Waiting for incoming return-requests...";
			BtsMvd = 0;
			while (1) 
			{
				if ((BtsMvd = recvfrom(sockfd, Buffer, sizeof(Buffer), 0,(struct sockaddr *)&their_addr, &sl)) == SOCKET_ERROR) 
				{
					// ERROR
					cout << "\n-- recvfrom error\n";
					return 0;
				}
				if (BtsMvd)
				{
					break;
				}
			}
			cout << "\nReturn-request received from: " << inet_ntoa(their_addr.sin_addr);
 
			BtsMvd = strlen(Buffer);
			Buffer[ BtsMvd ] = '*';
			Buffer[ BtsMvd + 1 ] = '\0';
 
			their_addr.sin_family = AF_INET;
			their_addr.sin_port = htons(MYPORT);
			their_addr.sin_addr.s_addr =inet_addr( inet_ntoa(their_addr.sin_addr) ); 
			memset(&(their_addr.sin_zero), '\0', 8); // zero the rest of the struct
 
			if ((new_fd = socket(AF_INET, SOCK_DGRAM, 0)) == SOCKET_ERROR)
			{
				// ERROR
				cout << "\n-- SOCKET error\n";
				return 0;
			}
 
			if ((BtsMvd = sendto(new_fd, Buffer, sizeof(Buffer), 0,(struct sockaddr *)&their_addr, sizeof(struct sockaddr))) != SOCKET_ERROR )
			{
				cout << "\nA return (" << Buffer << ") has been sent back.";
			} 
			else 
			{
				cout << "\nCould not return request.";
			}
		}
 
		goto GetChoice;
		return 0;
}

Your IP:  0.0.0.0

char Buffer[100];
struct hostent *h; // MEEEEE
 
	if (gethostname(Buffer, sizeof(Buffer))) {
		// ERROR
		cout << "\n-- HOST error 1\n";
		return 0;
	}
 
	if ((h = gethostbyname(Buffer)) == 0x0) {
		// ERROR
		cout << "\n-- HOST error 2\n";
		return 0;
	}
 
	cout << "Your IP: " << inet_ntoa(*((struct in_addr *)h->h_addr)) << "\n";