The Big Programming Thread - Page 21

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1. This is not a "do my homework for me" thread. If you have specific questions, ask, but don't post an assignment or homework problem and expect an exact solution.
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4. Use [code] tags to format code blocks.

Kaluba

Germany21 Posts

September 26 2010 14:21 GMT

#401

Hey,
do you also have a guide for VB6 and VB.NET? Would be really nice!
Thx

Adeny

Norway1233 Posts

October 07 2010 02:09 GMT

#402

This is killing me, here goes:
C#, TCP, network streams.

server code:


// sw is streamreader, sr is streamwrite. these work.
// Database.Register(string, string) is a custom function that returns a string response. i tried
// replacing with sw.WriteLine("durr"), but no response was recieved for the client

// the Database.Register function is reached and returns a string value.

// message is sr.ReadLine().
if (message == "newUser")
{
    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
}

Client code:


sw.WriteLine("newUser");
sw.WriteLine(name);
sw.WriteLine(pw);
                
// Execution stops on the ReadLine, as it should, but does not continue even when an answer is
// sent from the server.
return sr.ReadLine();

It seems to just block on the return indefinately. Oh and it works if I reply twice, what? Jeez I'm probably missing something painfully obvious...

Edit: I mean it blocks specifically on that return and awaits the servers answer.

haduken

Australia8267 Posts

October 07 2010 15:58 GMT

#403

On September 26 2010 23:02 Adeny wrote:
Let's ask some more questions! Weeee! Not going to edit because no one will answer if it doesn't get bumped.

This time, how do I sockets? Relax, I'll go more in depth, here's my current set up:

VM Linux with MySQL <- Server application (C#) <- Client application(C#). All well and good, in fact I can register and "log in" based on data from the database. However I'm stuck when it comes to handling multiple user connections. Now, I obviously want threads, but how do I "manage" the connections?

I'm thinking I should keep an array of users that connect, then make a separate thread for each user of course, and then dispose of the threads that aren't in use because users disconnected.

Makes sense right? But how do I go about doing that? I.E. Do I make one "master socket" that everyone connects to, then make a new thread every time someone connects to it, and somehow automagically transfer that client over to the new socket?

All in all I am confuse.

You should look into credential management in .NET and I thought concurrency is handled by the database most of the time.

tofucake

Hyrule19199 Posts

October 07 2010 16:52 GMT

#404

On October 07 2010 11:09 Adeny wrote:
This is killing me, here goes:
C#, TCP, network streams.

server code:
+ Show Spoiler +


// sw is streamreader, sr is streamwrite. these work.
// Database.Register(string, string) is a custom function that returns a string response. i tried
// replacing with sw.WriteLine("durr", but no response was recieved for the client

// the Database.Register function is reached and returns a string value.

// message is sr.ReadLine().
if (message == "newUser"
{
    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
}

Client code:


sw.WriteLine("newUser";
sw.WriteLine(name);
sw.WriteLine(pw);
                
// Execution stops on the ReadLine, as it should, but does not continue even when an answer is
// sent from the server.
return sr.ReadLine();

You can't just assume that you've received data. You need to check before you try to read.

Yiko

Germany104 Posts

October 07 2010 17:05 GMT

#405

On October 07 2010 11:09 Adeny wrote:
This is killing me, here goes:
C#, TCP, network streams.

+ Show Spoiler +

server code:


// sw is streamreader, sr is streamwrite. these work.
// Database.Register(string, string) is a custom function that returns a string response. i tried
// replacing with sw.WriteLine("durr"), but no response was recieved for the client

// the Database.Register function is reached and returns a string value.

// message is sr.ReadLine().
if (message == "newUser")
{
    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
}

Client code:


sw.WriteLine("newUser");
sw.WriteLine(name);
sw.WriteLine(pw);
                
// Execution stops on the ReadLine, as it should, but does not continue even when an answer is
// sent from the server.
return sr.ReadLine();

Have you tried flushing the serverside streamwriter?


    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
    sw.Flush();

I'm no .NET expert but that would be my first guess.

Adeny

Norway1233 Posts

October 07 2010 17:12 GMT

#406

On October 08 2010 01:52 tofucake wrote:
+ Show Spoiler +

On October 07 2010 11:09 Adeny wrote:
This is killing me, here goes:
C#, TCP, network streams.

server code:
+ Show Spoiler +


// sw is streamreader, sr is streamwrite. these work.
// Database.Register(string, string) is a custom function that returns a string response. i tried
// replacing with sw.WriteLine("durr"), but no response was recieved for the client

// the Database.Register function is reached and returns a string value.

// message is sr.ReadLine().
if (message == "newUser")
{
    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
}

Client code:


sw.WriteLine("newUser");
sw.WriteLine(name);
sw.WriteLine(pw);
                
// Execution stops on the ReadLine, as it should, but does not continue even when an answer is
// sent from the server.
return sr.ReadLine();

You can't just assume that you've received data. You need to check before you try to read.

Yes but sr.ReadLine() blocks the program (or thread) until data can be read. So when I step through it it reaches that ReadLine() and is in blocking mode, but when data is sent, it keeps blocking.

Adeny

Norway1233 Posts

October 07 2010 17:13 GMT

#407

On October 08 2010 02:05 Yiko wrote:
+ Show Spoiler +

On October 07 2010 11:09 Adeny wrote:
This is killing me, here goes:
C#, TCP, network streams.

+ Show Spoiler +

server code:


// sw is streamreader, sr is streamwrite. these work.
// Database.Register(string, string) is a custom function that returns a string response. i tried
// replacing with sw.WriteLine("durr"), but no response was recieved for the client

// the Database.Register function is reached and returns a string value.

// message is sr.ReadLine().
if (message == "newUser")
{
    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
}

Client code:


sw.WriteLine("newUser");
sw.WriteLine(name);
sw.WriteLine(pw);
                
// Execution stops on the ReadLine, as it should, but does not continue even when an answer is
// sent from the server.
return sr.ReadLine();

Have you tried flushing the serverside streamwriter?


    string name = sr.ReadLine();
    string pw = sr.ReadLine();
    sw.WriteLine(Database.Register(name, pw));
    sw.Flush();

I'm no .NET expert but that would be my first guess.

I'm using AutoFlush, is there any difference from just flushing manually with every send? Tried flushing manually, doesn't work. I read up and there weren't a lot of difference, mainly performance ones.

Adeny

Norway1233 Posts

October 07 2010 17:22 GMT

#408

On October 08 2010 00:58 haduken wrote:
+ Show Spoiler +

You should look into credential management in .NET and I thought concurrency is handled by the database most of the time.

I'll take a look at credential management, however wouldn't it be very bad to allow the client program direct access to a database? Seeing as you need to include the connection string somewhere, there's also packet forging.

Either way here's what I ended up with:

Server has a thread which checks for connections, if someone connects, a thread is created specifically for them which contains the interaction stuff. If this thread throws an exception I clean up and decrement the variable keeping track of how many connections I have.

Not the prettiest of solutions as it relies on an exception...

Adeny

Norway1233 Posts

October 08 2010 23:35 GMT

#409

On October 08 2010 02:12 Adeny wrote:

Show nested quote +

Yes but sr.ReadLine() blocks the program (or thread) until data can be read. So when I step through it it reaches that ReadLine() and is in blocking mode, but when data is sent, it keeps blocking.

If anyone wants to know I figured out what happened... Basically I had another thread on the client which I though it would have broken out of but I forgot the "break;", and so this reached a StreamReader.ReadLine() first and got the data from the server. I should've figured it out when it worked sending the same data twice...

Threads and sockets man, so confusing.

Cofo

United States1388 Posts

October 15 2010 01:03 GMT

#410

Hey TL programmers, I'm a second year (soon to be) CS major and I thought I'd stop by for some general advice.

Basically, I'm looking for an internship for this summer. However, the courses I'm taking this semester are more hardware/logic oriented, so I feel like I'm not really gaining skills that will be useful for a programming job. I've been messing around in Java on my own, but I was just wondering if there are any other things I could be doing or specific topics I should study independently that would help me secure some kind of internship. Or just any internship advice in general would be great. ^^ Thanks!

OPSavioR

Sweden1465 Posts

October 20 2010 23:39 GMT

#411

Where can i find good php tutorials?

haduken

Australia8267 Posts

October 21 2010 10:53 GMT

#412

www.php.net?

Haven't failed me yet.

Triscuit

United States722 Posts

October 26 2010 22:33 GMT

#413

Hi TL programmers. I'm a third year CS student right now at the University of Texas at Austin.

I guess I've come to a realization slowly over the past few semesters. I need help with programming. I don't think I am a *poor* programmer, but I really don't have any confidence in my ability to get larger projects done.

I don't think I have the experience necessary to help me easily think about data structures or algorithms in a disciplined way, and I think if I continue down this path, I'll continue to be a sub-par programmer and this will hurt me immensely in the long run. I don't really have issues with languages as much as I have trouble with the abstractions.

So, I the questions I ask of you fine programmers are: How do you practice these things? Do you have any references or textbooks that have been of particular value to you? What were things that you learned in the workplace that you wish you had known in school, or even when you were first finding a job?

Thanks for your help.

toadstool

Australia421 Posts

October 26 2010 22:52 GMT

#414

On October 27 2010 07:33 Triscuit wrote:
Hi TL programmers. I'm a third year CS student right now at the University of Texas at Austin.

I guess I've come to a realization slowly over the past few semesters. I need help with programming. I don't think I am a *poor* programmer, but I really don't have any confidence in my ability to get larger projects done.

I don't think I have the experience necessary to help me easily think about data structures or algorithms in a disciplined way, and I think if I continue down this path, I'll continue to be a sub-par programmer and this will hurt me immensely in the long run. I don't really have issues with languages as much as I have trouble with the abstractions.

So, I the questions I ask of you fine programmers are: How do you practice these things? Do you have any references or textbooks that have been of particular value to you? What were things that you learned in the workplace that you wish you had known in school, or even when you were first finding a job?

Thanks for your help.

The simple answer is: practice programming yourself. Make mistakes, learn why and how things work and you'll know more about how the language works and simple programming tricks and traps to avoid.

Mistakes are the best way to learn. If you make a new XML parser, and you luckily get it 100% correct the first time, you won't learn anything.

If you make it and spend 2 weeks figuring out the quirks and bugs, you'll know the system inside out. And you'll develop better code in the long run. I went through a rough patch during uni, but now I'm fairly confident in my code.

Also another tip is: the simpler the code is, the better. Don't try to do things complicated, you'll run into problems in the long run.

Triscuit

United States722 Posts

October 27 2010 02:45 GMT

#415

On October 27 2010 07:52 toadstool wrote:

Show nested quote +

Thanks for the reply. I have one question about this advice though. What should I practice on?

toadstool

Australia421 Posts

October 28 2010 04:49 GMT

#416

Grab your old assignments/projects from your University course, and firstly try to add more features. Then try to optimise how it all works, make it more efficient. Then lastly, change the user interface so it's more intuitive and user friendly.

this is great because you can go to job interviews and show them your project. Do all this in Java or .net

Or if you want to challenge yourself, create a basketball game simulation. Make each player read stats from XML documents, so you'll learn XML parsing as well (a very useful skill to have).

catamorphist

United States297 Posts

October 28 2010 06:11 GMT

#417

You don't need experience to think about data structures and algorithms in a disciplined way, you just need discipline. Don't fool yourself about what you understand; just think about it and put pen on paper until you do. If you couldn't implement it without consulting a reference, you don't fully understand it. (Of course, I'm not saying that everyone can have this level of understanding about many things all the time, but you should understand things once even if they slip partially from your mind later.)

In terms of practice, for data structures and algorithms specifically, TopCoder competitions. Generally, open-source.

It's not clear to me exactly which abstractions you mean when you cite trouble with abstractions. There are a lot of them.

Ygz

England370 Posts

October 28 2010 12:27 GMT

#418

On October 27 2010 07:33 Triscuit wrote:
Do you have any references or textbooks that have been of particular value to you?

http://www.amazon.co.uk/Programming-Principles-Practice-Developers-Library/dp/0321543726/ref=sr_1_1?ie=UTF8&s=books&qid=1288267580&sr=8-1

Read this. It doesn't matter if you don't already know C++, he teaches that as you progress. Bjarne uses C++ as his tool to demonstrate and teach how to construct real world code that is correct, simple and efficient. Based on your level of education you should have no problems working through this book, some problems are pretty tough but that's OK, Bjarne is not here to teach you toy code and meaningless concepts.

There are 27 chapters broken into 4 parts:
Part 1 - The basics.
Part 2 - Input/Output
Part 3 - Data and Algorithms
Part 4 - Broadening the View.

Go here for a detailed look at what each part contains.
http://www2.research.att.com/~bs/programming_toc.pdf

What you'll learn from this, is what you will need in the real world if you intend one day to write non trivial code. Also, a majority of the concepts and practices are to a degree, language agnostic. So you can transfer to another language no problem once you've completed the book.

For me it's one of the best technical books I've read, right up there with Code complete and K&R C.