C++ TCP Socket Program

I was looking around for a sample TCP socket program written in C++ that might make working with TCP sockets less mysterious. I expected to find a flood of things to pick from, but that really wasn’t the case.

The Details
OK, I only looked for a few minutes, to be honest. The one I did settle on seems adequate. It’s sufficiently old, however, that it doesn’t actually work as-is. Probably if it did I wouldn’t even mention it. So I thought it was worth repeating here, with some tiny semantic updates.

What I used is from this web page: I was really only interested in the TCP echo client. It’s a good stand-ion for any TCP client I think.

Here’s TCPechoClient.cpp:

 *   C++ sockets on Unix and Windows
 *   Copyright (C) 2002
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   GNU General Public License for more details.
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
// taken from
#include "PracticalSocket.h"  // For Socket and SocketException
#include <iostream>           // For cerr and cout
#include <cstdlib>            // For atoi()
#include <cstring>            // author forgot this
using namespace std;
const int RCVBUFSIZE = 32;    // Size of receive buffer
int main(int argc, char *argv[]) {
  if ((argc < 3) || (argc > 4)) {     // Test for correct number of arguments
    cerr << "Usage: " << argv[0]
         << " <Server> <Echo String> [<Server Port>]" << endl;
  string servAddress = argv[1]; // First arg: server address
  char *echoString = argv[2];   // Second arg: string to echo
// DrJ test
//  echoString = "GET / HTTP/1.0\n\n";
  int echoStringLen = strlen(echoString);   // Determine input length
  unsigned short echoServPort = (argc == 4) ? atoi(argv[3]) : 7;
  try {
    // Establish connection with the echo server
    TCPSocket sock(servAddress, echoServPort);
    // Send the string to the echo server
    sock.send(echoString, echoStringLen);
    char echoBuffer[RCVBUFSIZE + 1];    // Buffer for echo string + \0
    int bytesReceived = 0;              // Bytes read on each recv()
    int totalBytesReceived = 0;         // Total bytes read
    // Receive the same string back from the server
    cout << "Received: ";               // Setup to print the echoed string
    while (totalBytesReceived < echoStringLen) {
      // Receive up to the buffer size bytes from the sender
      if ((bytesReceived = (sock.recv(echoBuffer, RCVBUFSIZE))) <= 0) {
        cerr << "Unable to read";
      totalBytesReceived += bytesReceived;     // Keep tally of total bytes
      echoBuffer[bytesReceived] = '\0';        // Terminate the string!
      cout << echoBuffer;                      // Print the echo buffer
    cout << endl;
    // Destructor closes the socket
  } catch(SocketException &e) {
    cerr << e.what() << endl;
  return 0;

Note the cstring header file I needed to include. The standard must have changed to require this since the original code was published.

Then I neeed PracticalSocket.h, but that has no changes from the original version: “, and his Makefile is also just fine: For the fun of it I also set up the TCP Echo Server:


make TCPEchoclient

and you should be good to go. How to test this TCPEchoClient against your web server? I found that the following works:

~/TCPEchoClient 'GET / HTTP/1.0
' 80

which gives this output:

Received: HTTP/1.1 301 Moved Permanently
Date: Thu, 23 Feb 2012 17:19:02

which, now that I analyze it, looks cut-off. Hmm. Because with curl I have:

curl -i

HTTP/1.1 301 Moved Permanently
Date: Thu, 23 Feb 2012 17:19:43 GMT
Server: Apache/2.2.16 (Ubuntu)
X-Powered-By: PHP/5.3.3-1ubuntu9.5
Vary: Accept-Encoding
Content-Length: 2
Content-Type: text/html

I guess that’s what you get for demo code. At this point I don’t have a need to sort it out so I won’t. Perhaps we’ll come back to it later. Looking at it, I see the received buffer size is quite small, 32 bytes. I tried to set that to a reasonable value, 200 MBytes, but get a segmentation fault. The largest I could manage, after experiementation, is 10000000 bytes:

//const int RCVBUFSIZE = 32;    // Size of receive buffer
const int RCVBUFSIZE = 10000000;    // Size of receive buffer - why is 10 MB the max. value??

and this does indeed give us the complete output from our web server home page now.

There is some demo C++ code which creates a useable class for dealing with TCP sockets. There might be some work to do before it could be used in a serious application, however.

One reply on “C++ TCP Socket Program”

Hi Dr John,

thanks a lot for this example.
I try to compile it with VS 2010 on an win 7 machine 64 bit.
I got PracticalSocket.h and PracticalSocket.cpp and inserted them in the project.
My attempt to compile it for win32 fails because of many linker errors here just one example.
PracticalSocket.obj : error LNK2019: unresolved external symbol _socket@12 referenced in function “protected: __thiscall Socket::Socket(int,int)” (??0Socket@@IAE@HH@Z)

do you have any idea how to fix it?
have you an idea how long would the latency of the socket be?
Thanks a lot in advance

All the best

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