C++ Hello TCP Client


Example

This program is complimentary to Hello TCP Server program, you can run either of them to check the validity of each other. The program flow is quite common with Hello TCP server, so make sure to take a look at that too.

Here's the code -

#include <cstring>
#include <iostream>
#include <string>

#include <arpa/inet.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>


int main(int argc, char *argv[])
{
    // Now we're taking an ipaddress and a port number as arguments to our program
    if (argc != 3) {
        std::cerr << "Run program as 'program <ipaddress> <port>'\n";
        return -1;
    }


    auto &ipAddress = argv[1];
    auto &portNum   = argv[2];

    addrinfo hints, *p;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family   = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags    = AI_PASSIVE;

    int gAddRes = getaddrinfo(ipAddress, portNum, &hints, &p);
    if (gAddRes != 0) {
        std::cerr << gai_strerror(gAddRes) << "\n";
        return -2;
    }

    if (p == NULL) {
        std::cerr << "No addresses found\n";
        return -3;
    }

    // socket() call creates a new socket and returns it's descriptor
    int sockFD = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
    if (sockFD == -1) {
        std::cerr << "Error while creating socket\n";
        return -4;
    }

    // Note: there is no bind() call as there was in Hello TCP Server
    // why? well you could call it though it's not necessary
    // because client doesn't necessarily has to have a fixed port number
    // so next call will bind it to a random available port number

    // connect() call tries to establish a TCP connection to the specified server
    int connectR = connect(sockFD, p->ai_addr, p->ai_addrlen);
    if (connectR == -1) {
        close(sockFD);
        std::cerr << "Error while connecting socket\n";
        return -5;
    }

    std::string reply(15, ' ');

    // recv() call tries to get the response from server
    // BUT there's a catch here, the response might take multiple calls
    // to recv() before it is completely received
    // will be demonstrated in another example to keep this minimal
    auto bytes_recv = recv(sockFD, &reply.front(), reply.size(), 0);
    if (bytes_recv == -1) {
        std::cerr << "Error while receiving bytes\n";
        return -6;
    }

    std::cout << "\nClient recieved: " << reply << std::endl;
    close(sockFD);
    freeaddrinfo(p);

    return 0;
}