Hey! Socket programming got you down? Is this stuff just a little too difficult to figure out from the man pages? You want to do cool Internet programming, but you don't have time to wade through a gob of structs trying to figure out if you have to call bind() before you connect(), etc., etc.
Well, guess what! I've already done this nasty business, and I'm dying to share the information with everyone! You've come to the right place. This document should give the average competent C programmer the edge s/he needs to get a grip on this networking noise.
This document has been written as a tutorial, not a reference. It is probably at its best when read by individuals who are just starting out with socket programming and are looking for a foothold. It is certainly not the complete guide to sockets programming, by any means.
Hopefully, though, it'll be just enough for those man pages to start making sense... :-)
The code contained within this document was compiled on a Linux PC using Gnu's gcc compiler. It should, however, build on just about any platform that uses gcc. Naturally, this doesn't apply if you're programming for Windows--see the section on Windows programming, below.
This official location of this document is at California State University, Chico, at http://www.ecst.csuchico.edu/~beej/guide/net/.
When compiling for Solaris or SunOS, you need to specify some extra command-line switches for linking in the proper libraries. In order to do this, simply add "-lnsl -lsocket -lresolv" to the end of the compile command, like so:
$ cc -o server server.c -lnsl -lsocket -lresolv |
If you still get errors, you could try further adding a "-lxnet" to the end of that command line. I don't know what that does, exactly, but some people seem to need it.
Another place that you might find problems is in the call to setsockopt(). The prototype differs from that on my Linux box, so instead of:
int yes=1; |
enter this:
char yes='1'; |
As I don't have a Sun box, I haven't tested any of the above information--it's just what people have told me through email.
I have a particular dislike for Windows, and encourage you to try Linux, BSD, or Unix instead. That being said, you can still use this stuff under Windows.
First, ignore pretty much all of the system header files I mention in here. All you need to include is:
#include <winsock.h> |
Wait! You also have to make a call to WSAStartup() before doing anything else with the sockets library. The code to do that looks something like this:
#include <winsock.h>
{
WSADATA wsaData; // if this doesn't work
//WSAData wsaData; // then try this instead
if (WSAStartup(MAKEWORD(1, 1), &wsaData) != 0) {
fprintf(stderr, "WSAStartup failed.\n");
exit(1);
}
|
You also have to tell your compiler to link in the Winsock library, usually called wsock32.lib or winsock32.lib or somesuch. Under VC++, this can be done through the Project menu, under Settings.... Click the Link tab, and look for the box titled "Object/library modules". Add "wsock32.lib" to that list.
Or so I hear.
Finally, you need to call WSACleanup() when you're all through with the sockets library. See your online help for details.
Once you do that, the rest of the examples in this tutorial should generally apply, with a few exceptions. For one thing, you can't use close() to close a socket--you need to use closesocket(), instead. Also, select() only works with socket descriptors, not file descriptors (like 0 for stdin).
There is also a socket class that you can use, CSocket. Check your compilers help pages for more information.
To get more information about Winsock, read the Winsock FAQ and go from there.
Finally, I hear that Windows has no fork() system call which is, unfortunately, used in some of my examples. Maybe you have to link in a POSIX library or something to get it to work, or you can use CreateProcess() instead. fork() takes no arguments, and CreateProcess() takes about 48 billion arguments. If you're not up to that, the CreateThread() is a little easier to digest...unfortunately a discussion about multithreading is beyond the scope of this document. I can only talk about so much, you know!
I'm generally available to help out with email questions so feel free to write in, but I can't guarantee a response. I lead a pretty busy life and there are times when I just can't answer a question you have. When that's the case, I usually just delete the message. It's nothing personal; I just won't ever have the time to give the detailed answer you require.
As a rule, the more complex the question, the less likely I am to respond. If you can narrow down your question before mailing it and be sure to include any pertinent information (like platform, compiler, error messages you're getting, and anything else you think might help me troubleshoot), you're much more likely to get a response. For more pointers, read ESR's document, How To Ask Questions The Smart Way.
If you don't get a response, hack on it some more, try to find the answer, and if it's still elusive, then write me again with the information you've found and hopefully it will be enough for me to help out.
Now that I've badgered you about how to write and not write me, I'd just like to let you know that I fully appreciate all the praise the guide has received over the years. It's a real morale boost, and it gladdens me to hear that it is being used for good! :-) Thank you!
You are more than welcome to mirror this site, whether publically or privately. If you publically mirror the site and want me to link to it from the main page, drop me a line at <beej@piratehaven.org>.
If you want to translate the guide into another language, write me at <beej@piratehaven.org> and I'll link to your translation from the main page.
Feel free to add your name and email address to the translation.
Sorry, but due to space constraints, I cannot host the translations myself.
Beej's Guide to Network Programming is Copyright © 1995-2001 Brian "Beej" Hall.
This guide may be freely reprinted in any medium provided that its content is not altered, it is presented in its entirety, and this copyright notice remains intact.
Educators are especially encouraged to recommend or supply copies of this guide to their students.
This guide may be freely translated into any language, provided the translation is accurate, and the guide is reprinted in its entirety. The translation may also include the name and contact information for the translator.
The C source code presented in this document is hereby granted to the public domain.
Contact <beej@piratehaven.org> for more information.