通过TCP与android（socket客户端）和c ++（socket服务器）连接

Question

i have an implementation to do in a college project, and i dont know how to avchive it!. my problem its like the title say, conect android with c++ via sockets.

c++ must manage at least a pair of sockets clients (android Devices) or more. so i try ...

#include <iostream>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdlib.h>
#include<unistd.h>

using namespace std;

int main()
{
    int client, server;
    int portnum = 1500;
    bool isExit = false;
    int bufsize = 1024;
    char buffer[bufsize];

    struct sockaddr_in server_addr;
    socklen_t size;

    //init socekt

    client = socket(AF_INET, SOCK_STREAM, 0);

    if(client < 0){
        cout << "Error Estableciendo la conexion" << endl;
    }

    cout <<"server Socket conexion creada" << endl;

    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htons(INADDR_ANY);
    server_addr.sin_port = htons(portnum);


    //biding soket

    if(bind(client,(struct sockaddr*)&server_addr,sizeof(server_addr)) < 0){
        cout << "Error Biding Socket" << endl;
        exit(1);
    }

    size= sizeof(server_addr);
    cout << "buscando clientes" << endl;

    //escuchando sokets

    listen(client,1);

    //accept client

    server = accept(client, (struct sockaddr*)&server_addr, &size);

    if(server < 0){
        cout<< "Error al Aceptar" << endl;
        exit(1);
    }

    while(server >0){
        strcpy(buffer,"server conectado---\n");
        send(server,buffer,bufsize,0);

        cout <<"conectado con el cliente" << endl;
        cout << "Ingresad # paara terminar la conexion" << endl;

        cout <<"client: ";
        do{
            recv(server,buffer,bufsize,0);
            cout << "buffer" << " ";
            if(*buffer == '#'){
                *buffer = '*';
                isExit=true;
            }
        }while(*buffer != '*');

        do{
            cout << "\n server: ";
            do{
                cin >> buffer;
                send(server,buffer,bufsize,0);
                if(*buffer == '#'){
                    send(server,buffer,bufsize,0);
                    *buffer = '*';
                    isExit=true;
                }
            }while(*buffer != '*');

            cout << "Client: ";

            do{
                recv(server,buffer,bufsize,0);
                cout << buffer << " ";
                if(*buffer == '#'){
                    *buffer = '*';
                    isExit = true;
                }
            }while(*buffer != '*');
        }while(isExit);

        cout << "Conection Terminated..." << endl;
        cout << "Goodbye..." << endl;
        isExit =false;
        exit(1);
    }
    close(client);
    return 0;
}

to listen every conection (please if you see bad logic in my code let me know it and what i need to do to fix it)

and in android i make something like this in a class that its called from an activity only for testing...

import java.net.Socket;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Socktest {

    public void prueba() {
        try {
            Socket sock = new Socket("127.0.0.1",1234);

            // Your Java Code Verbatim:
            BufferedReader br = new BufferedReader(new InputStreamReader(sock.getInputStream()));
            String test = br.readLine();

            System.out.println(test);
            sock.close();
        } catch (Exception ex) {
            System.out.println(ex.getCause().toString());
        }
    }
}

(please if you see bad logic let me knowit because i want to learn more from my failures)

and the server goes fine when i compiled, its standing by to recive a new conection but when a luch the android activity and i run the "conection class" it says access denied, i am working on linux mint if that afect...

i am going to be gratfull with you coments, suggestions and advices.

Answer 1

Socket sock = new Socket("127.0.0.1",1234); this line is your problem right here, 127.0.0.1 is the local loop IP, its actually an IP address that maps to the device the code is on, so your android client is never connecting to the machine where the c++ code is running, instead what you need to do is find the IP address of the machine your c++ code is running on then change 127.0.0.1 to that IP address.

If you're mobile is connected to a wifi router to which your c++ server is connected to, then this IP address will be the local IP address, and everything is simple

If you're mobile is connected to some mobile network, and your server is on a different network, then you need to find out the IP address of your machine exposed to the world (depending on Internet service providers configuration you might have an IP address that remains static, or an IP address that changes every time your connection to the ISP server resets) You can find your machines exposed IP address by going to websites like http://whatismyipaddress.com/ , then if your machine is behind a router, you need to do port forwarding (in this case forward your port 1234 to your machines local IP address) you can take a look at this guide to understand how to do that.

So to avoid the complexity in the 2nd step I advise you to connect your mobile and your server in same local network (ie your LAN) using a wifi router.

Ways to find the IP address of your machine:

In linux based machines just open a terminal and type ifconfig and look at eth0 your IP address will be right after inet addr: , for example like this inet addr:10.99.123.23