Setting a timeout when using connect() in C++

Question

I'm using sockets in c++ on linux to connect to a server using connect(), but it doesn't seem to have a timeout value. What would be the easiest/best way to give it a timeout of a few seconds. I'll post the code I have up to, and including, the blocking call to connect():

using namespace std;
int main( int argc, char* argv[] )
{
  // Interpret the command line arguments
  string uri_string = "";

  if ( argc != 2 )
  {
    cerr << "Usage: " << argv[0];
    cerr << " <URI>" << endl;
    return 1;
  }
  else
  {
    uri_string = argv[1];
  }

  // Create URI object and have it parse the uri_string
  URI *uri = URI::Parse(uri_string);

  if ( uri == NULL )
  {
    cerr << "Error: Cannot parse URI." << endl;
    return 2;
  }

  // Check the port number specified, if none use port 80
  unsigned port = 80;
  if ( uri->Is_port_defined() )
  {
    port = uri->Get_port();
  }

  // Create TCP socket and connect to server
  int tcp_sock = socket( AF_INET, SOCK_STREAM, 0 );
  if ( tcp_sock < 0 )
  {
    cerr << "Unable to create TCP socket." << endl;
    return 3;
  }

  sockaddr_in server;
  socklen_t slen = sizeof(server);

  server.sin_family = AF_INET;
  server.sin_port = htons( port );
  cout << "Resolving " << uri->Get_host() << "... ";
  hostent *hostp = gethostbyname( uri->Get_host().c_str() );
  memcpy( &server.sin_addr, hostp->h_addr, hostp->h_length );

  struct in_addr **pptr;
  pptr = (struct in_addr **)hostp->h_addr_list;

  string ip_addr = "";
  while( *pptr != NULL ) {
    ip_addr += inet_ntoa(**(pptr++));
  }
  cout << ip_addr << endl;

  cout << "Connecting to " << uri->Get_host() << "|" << ip_addr << "|:";
  cout << port << "... ";
  if ( connect( tcp_sock, (sockaddr*)&server, slen ) < 0 )
  {
    cerr << "Unable to connect to server via TCP." << endl;
    close( tcp_sock );
    return 4;
  }
  cout << "connected." << endl;

  // rest of code
}

Answer 1

Make the socket a non-blocking socket, and then use select() or poll() with a timeout value to check for writability. If the select() returns with a timeout you did not connect in time, and you can close the socket and deal with the connection failure. If it returns with a completion, everything is fine and you can proceed.