A file descriptor is simply an integer associated with an open file. right now , but I’m going to answer it anyway: You make a call to the socket() system routine. System Calls or Bust – What is a socket? – Struct sockaddr and pals. Praise for Socket Programming Guide. When I first wrote Beej’s Guide to.

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What is a socket?

Beej’s Guide to Network Programming Using Internet Sockets

Two Types of Internet Sockets 2. Low level Nonsense and Network Been 3. IP Addresses, struct s, and Data Munging 3. IP Addresses, versions 4 and 6 3. IP Addresses, Part Deux 4. Jumping from IPv4 to IPv6 5. System Calls or Bust 5. A Simple Stream Server 6. A Simple Stream Client 6. Slightly Advanced Techniques 7. Handling Partial send s 7. Serialization—How to Pack Data 7. Son of Data Encapsulation 7. 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 struct s trying to figure out if you have to call bind before you connectetc.

I’ve already done this nasty business, and I’m dying to share the information with everyone! You’ve come to the right place. And check it out: I’ve finally caught up with the future just in the nick of time, too! This document has been written as a tutorial, not a complete reference. It is probably at beje 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 and total 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 aocket section on Windows programmingbelow.

This official location of this document is http: There you will also find example code and translations of the guide into various languages. To buy nicely bound print copies some call them “books”visit http: I’ll appreciate the purchase because it helps sustain my document-writing lifestyle!

When compiling for Solaris or SunOS, you need to specify some extra command-line sovket 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:. If you berj get errors, you could try further adding a ” -lxnet ” to the end of that command line. I don’t know what that does, brej, 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:. 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.


At this point in the guide, historically, I’ve done a bit of bagging on Windows, simply due to the fact that I don’t like it very much. But I should really be fair and tell bej that Windows has a huge install base and is obviously a perfectly fine operating system.

They say absence makes the heart grow fonder, and in this case, I believe it to be true. Or maybe socjet age. But what I can say is that after a decade-plus of not using Microsoft OSes for my personal work, I’m zocket happier! As such, I can sit back and safely say, “Sure, feel free to use Windows! Ok yes, it does make me grit my teeth to say that. But people like what they like, and you Windows folk will be pleased to know that this information is generally applicable to you guys, with a few minor changes, if any.

One cool thing you can do is install Cygwinwhich is a collection of Unix tools for Windows. I’ve heard on the grapevine that doing so allows all these programs to compile unmodified. But some of you might want to do things the Pure Windows Way. That’s very gutsy of you, and this is what you have to do: I’m supposed to be Windows-friendly er these days This is what you’ll have to do unless you install Cygwin!

All you need to include is:. You also have to make a call to Oscket before doing anything else with the sockets library. The code to do that sockeet something like this:. You soocket have to tell your compiler to link in the Winsock library, beeej called wsock 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 closesocketinstead. Also, select only works sockdt 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. Finally, I hear that Windows has no fork system call which is, unfortunately, used in some of my examples. If you’re not up to that, the CreateThread is a little easier to bej 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 befj won’t ever have the time to give the detailed answer you require.

Beej’s Guide to Network Programming Using Internet Sockets

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 troubleshootyou’re much more likely to get a response.


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! You are more than welcome to mirror this site, whether publicly or privately.

If you publicly mirror the site and want me to link to it from the main page, drop me a line at beej beej. If you want to translate the guide into another language, write me at beej beej. Feel free to add your name and contact info to the translation. If you want me to host the translation, just ask. I’ll also link to it if you want to host it; either way is fine. With specific exceptions for source code and translations, below, this work is licensed under the Creative Commons Attribution- Noncommercial- No Derivative Works 3.

To view a copy of this license, visit http: One specific exception to the “No Derivative Works” portion of the license is as follows: The same license restrictions apply to the translation as to the original guide.

The translation may also include the name and socke information for the translator. The C source code presented in this document is hereby granted to the public domain, and is completely free of any license restriction. You hear talk of ” sockets” all the time, and perhaps you are wondering just what they are exactly. Ok—you may have heard some Unix hacker state, “Jeez, everything in Unix is a file!

A file descriptor is simply an integer associated with an open file. But and here’s the catchthat file can be a network connection, a FIFO, a pipe, a bewj, a real on-the-disk file, or just about anything else. Everything in Unix is a file! So when you want to communicate with another program over the Soclet you’re gonna do it through a file descriptor, you’d better believe it.

You make a call to the socket system socke. It returns the socket descriptor, and you communicate through it using the specialized send and recv man sendman recv socket calls.

This document deals only with the first: There are two types of Internet sockets? There are more, but I didn’t want to scare you.