Beej’s Guide to C Programming. Beej’s Guide to Unix Interprocess Communication. (Click here for other guides!). Beej’s Guide to Network Programming. Using Internet Sockets.
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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 bejs 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. This document has been written as gguide tutorial, not a reference. It is probably at its best when read by individuals who are just starting out geejs 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 beesj 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 programmingbelow.
This official location of this document is at California State University, Chico, at http: 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, beeejs so:.
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:.
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. That being said, beeus can still use this stuff under Windows. First, ignore pretty much gujde of the system header files I mention in here. All you need to include is:. You also have to make a call to WSAStartup before bewjs anything else with the sockets library. The code to do that looks something like this:. You also have to tell your compiler to link in the Winsock library, usually 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 guids a socket–you need to use closesocketinstead.
Also, select only works with huide 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.
Beej’s Guide to Network Programming
Finally, I hear that Brejs 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 gulde easier to digest I can only talk about so much, you know! I’m generally available guidf help out with email questions berjs feel gulde 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 gide. 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 beejss.
If you can narrow down your question before mailing it and be sure to include guidd pertinent information like vuide, 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 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 beej. If you want to translate the guide into another language, write me at beej beej. 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.
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 terminal, a real on-the-disk file, or just about anything else. Everything in Unix is a file!
Beej’s Guide to Network Programming
So when you want to communicate with another program over the Internet you’re gonna do it through a file descriptor, you’d guids believe it. You make a call to the socket system routine.
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. I’m only going to talk about two types here. Except for this sentence, where I’m going to tell you that “Raw Sockets” are also very powerful and you should look them up.
What are the two types? Datagram sockets are sometimes called “connectionless sockets”.
Though they can be connect ‘d if you really want. See connectbelow. Stream sockets are reliable two-way connected communication streams.
If you output two items into the socket in the order “1, 2”, they will arrive in the order “1, 2” at the opposite end. They will also be error free. Any errors you do encounter are figments of your own huide mind, and are not to be discussed here. What uses stream sockets? Well, you may have geejs of the telnet application, yes?
It uses stream sockets. All the characters you type need to arrive in the same order you type them, right? Also, web browsers use the HTTP protocol which uses stream sockets to get pages.
How do stream sockets achieve this high level of data transmission quality? TCP makes sure your data arrives sequentially and error-free. IP ghide primarily with Internet routing and is not generally responsible for data integrity. What about Datagram sockets? Why are they called connectionless? What is the deal, here, anyway? Why are they unreliable? Well, here are some facts: It may arrive out of order. If it arrives, the data within the packet will be error-free.
Why are guidf connectionless? Well, basically, it’s because you don’t have to maintain an open connection as you do with stream sockets. You just build a packet, slap an IP header on it with destination information, and send it out. They are generally used for packet-by-packet transfers of information.
Beeus example, the tftp protocol says that for each packet that gets sent, the recipient has to send back a packet that says, “I got it!
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If the sender of the original packet gets no reply in, say, five seconds, he’ll re-transmit the packet until he finally gets an ACK. Practically, you can probably skip this section.
It’s good background, however. Hey, kids, it’s time to learn about Data Encapsulation! This is very very important. It’s so important that you might just learn about it if you take the networks course here at Chico State .