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  • Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

    - by Ricket
    Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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  • suggestions on syntax to express mathematical formula concisely

    - by aaa
    hello. I am developing functional domain specific embedded language within C++ to translate formulas into working code as concisely and accurately as possible. I post prototype in the comment, it is about 2 hundred lines long. Right now my language looks something like this (well, actually is going to look like): // implies two nested loops j=0:N, i=0,j (range(i) < j < N)[T(i,j) = (T(i,j) - T(j,i))/e(i+j)]; // implies summation over above expression sum(range(i) < j < N))[(T(i,j) - T(j,i))/e(i+j)]; I am looking for possible syntax improvements/extensions or just different ideas about expressing mathematical formulas as clearly and precisely as possible (in any language, not just C++). Can you give me some syntax examples relating to my question which can be accomplished in your language of choice which consider useful. In particular, if you have some ideas about how to translate the above code segments, I would be happy to hear them. Thank you just to clarify and give actual formula, my short-term goal is to express the following expression concisely where values in <> are already computed as 4-dimensional array

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  • Is MS Access still the most efficient RAD tool for small-scale custom apps?

    - by FastAl
    Of the many other development tools I've used, nothing holds a candle to the 'Functionality to Development Effort' ratio of MS Access. The reason I am asking is that I have been out of the language selection process for a few years, working on a large .Net system, and am only anecdotally familiar with the latest development tools outside the .Net world. I'm well aware of the limitations of Access, but for a limited concurrency (usually only 1 user at a time), small business, custom app, has anybody found a comparable end-to-end solution or combination that comes close? It doesn't have to be free, open source, or even Windows based. It just has to allow the same speed of development and maintenance, and maybe even provide some additional amenities like seamless autointegration with a server-based DB Engine (like Access does with its own 'Jet' dbms), better web support, and a file format more compatible with source control. I don't want to miss out on anything. Please share your development experience with your suggestions. Thanks.

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  • How can I write simulations in Erlang?

    - by rick
    Hi guys, I want to do some numerical stuff in Erlang like this: You've got an array with the following values: [2,3,4] In each iteration, you calculate 0.1 * [n-1] + 0.7 *[n] + 0.2 * [n+1] This becomes the new [n]. If n == 0 then [n-1] = 0. If [n] == length of array then [n] = 0. So I try an example: [2,3,4] calculations: 0.1 * 0 + 0.7 * 2 + 0.2 * 3 = 2 0.1 * 2 + 0.7 * 3 + 0.2 * 4 = 3.1 0.1 * 3 + 0.7 * 4 + 0.2 * 0 = 3.1 So [2,3,4] becomes to [2, 3.1, 3.1] after one iteration. I know how to write this in a non-functional language like C. But I have difficulties to imagine, how this could be done in Erlang. I found some tutorials on how you read a file to a list. So this is not the problem. How can I spawn different Erlang processes that each process has one element of the list? How can I do calculations by communicating with 'the neighbors', so that the neighbors know where their neigbors are generically, without specifying each? How can I collect the data into a list? Eventually, is it possible to solve that problem in Erlang at all? Thanks for your help.

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  • how works applications which blocks web sites?

    - by noisy
    I know only one low-level way of blocking websites - hosts file. However, it is obvious that main stream programs has some other way of achieving this. I have an idea for new model of this kind of program, but without possibility of blocking sites it is useless :(

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  • Which messaging interfaces can BlackBerry apps modify?

    - by humble coffee
    Does the native Blackberry API allow for the modification of any messaging interface? For example, I'd like to be able to build an app that added a button at the bottom of a received message which says 'translate this'. I've heard that this kind of thing is possible using J2ME plus the native BlackBerry API. Can this be done for all kinds of messages, eg SMS, email and BB messaging? The translation aspect is not relevant, it just provides the context for the kind of feature I'm after.

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  • Is there any reason for a blocking call to winsock send() function on Vista to return immediately ?

    - by ivymike
    Hi All, Is there any reason for a blocking call to winsock's send() function on Vista to return immediately ? It works with expected delay on XP and below. I'm wondering if this has got anything to do with auto-tuning feature of Vista. Code: char *pBuffer; // pointer to data int bytes; // total size int i = 0, j=0; while (i < bytes) { j = send(m_sock, pBuffer+i, bytes-i, 0); i+=j; } Thanks, Pavan

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  • How do I define a monadic function to work on a list in J?

    - by Gregory Higley
    Let's say I have the following J expression: # 3 ((|=0:)#]) 1+i.1000 This counts the number of numbers between 1 and 1000 that are evenly divisible by 3. (Now, before anyone points out that there's an easier way to do this, this question is about the syntax of J, and not mathematics.) Let's say I define a monadic function for this, as follows: f =: monad define # y ((|=0:)#]) 1+i.1000 ) This works great with a single argument, e.g., f 4 250 If I pass a list in, I get a length error: f 1 2 3 |length error: f Now, I completely understand why I get the length error. When you substitute the list 1 2 3 for the y argument of the monad, you get: # 1 2 3 ((|=0:)#]) 1+i.1000 If you know anything about J, it's pretty clear why the length error is occurring. So, I don't need an explanation of that. I want to define the function such that when I pass a list, it returns a list, e.g., f 1 2 3 1000 500 333 How can I either (a) redefine this function to take a list and return a list or (b) get the function to work on a list as-is without being redefined, perhaps using some adverb or other technique?

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  • Easy way to convert c code to assembly?

    - by Bob
    Is there an easy way (like a free program) that can covert c/c++ code to x86 assembly? I know that any c compiler does something very similar and that I can just compile the c code and then disassemble the complied executable, but that's kind of an overkill, all I want is to convert a few lines of code. Does anyone know of some program that can do that?

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  • After C++ - Python or Java?

    - by carleeto
    I'm fast approaching the point in my coding where I would like to quickly write object oriented code in languages other than C++ for a variety of reasons. After a lot of research, my choices have pretty much narrowed down to Python and Java. I'm leaning towards Python because of its relationship to C, but with Java, from what I can see, I get a good introduction to using and creating test suites with Eclipse - there is also Processing which is pulling me towards Java. I'm not the kind of guy to tackle two languages at once, so which one would you recommend and why? What I want at the end is to have an additional language I can use for rapid development. Ease of learning isn't important to me as I'm willing to put in the time regardless. Ability to use the new language widely is.

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  • Udp server sending only 0 bytes of data

    - by mawia
    Hi all, This is a simple Udp server.I am trying to transmit data to some clients,but unfortunetly it is unable to transmit data.Though send is running quite successfully but it is returning with a return value meaning it has send nothing.On the client they are receiving but again obviously,zero bytes. void* UdpServerStreamToClients(void *fileToServe) { int sockfd,n=0,k; struct sockaddr_in servaddr,cliaddr; socklen_t len; char dataToSend[1000]; sockfd=socket(AF_INET,SOCK_DGRAM,0); bzero(&servaddr,sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_addr.s_addr=htonl(INADDR_ANY); servaddr.sin_port=htons(32000); bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr)); FILE *fp; if((fp=fopen((char*)fileToServe,"r"))==NULL) { printf("can not open file "); perror("fopen"); exit(1); } int dataRead=1; while(dataRead) { len = sizeof(cliaddr); if((dataRead=fread(dataToSend,1,500,fp))<0) { perror("fread"); exit(1); } //sleep(2); for(list<clientInfo>::iterator it=clients.begin();it!=clients.end();it++) { cliaddr.sin_family = AF_INET; inet_aton(inet_ntoa(it->addr.sin_addr),&cliaddr.sin_addr); cliaddr.sin_port = htons(it->udp_port); n=sendto(sockfd,dataToSend,sizeof(dataToSend),0,(struct sockaddr *)&cliaddr,len); cout<<"number of bytes send by udp: "<< n << endl; printf("SEND this message %d : %s to %s :%d \n",n,dataToSend,inet_ntoa(cliaddr.sin_addr), ntohs(cliaddr.sin_port)); } } } I am checking the value of sizeof(dataTosend) and it is pretty much as expected ie thousand ie the size of buffer. Are you people seeing some possible flaw in it. All of the help in this regard will be appreciated. Thanks!

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  • What does $this generally mean in PHP?

    - by xczzhh
    I am really new to PHP, so I am kind of confused seeing these different operators all day. Here is some code I came across when watching a video tutorail, I'd appreciate it if some could explain a little bit: function index() { $config = Array( 'protocol' => 'smtp', 'smtp_host' => 'ssl://smtp.googlemail.com', 'smtp_port' => 465, 'smtp_user' => '[email protected]', 'smtp_pass' =>'password', ); $this->load->library('email', $config); $this->email->set_newline("\r\n"); $this->email->from('[email protected]', 'Jerry'); $this->email->to('[email protected]'); $this->email->subject('this is an email test'); $this->email->message('this is test message!'); if($this->email->send()) { echo 'Your email was sent'; } else { show_error($this->email->print_debugger()); } } ...

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  • Jquery canvas touch count

    - by user897764
    Can someone help me with a script I'm working with. http://jsfiddle.net/InVAMPED/XsG4e/4/ What I'm trying to achieve is placing a image where the user touches(ipad). There will be say 5 images that will each get attached once only. So first touch places img1, second touch imag2 etc untill all the images have been placed. Problem with my fsfiddle example is that when on ipad it doesnt count the first touch so you place the first image twice. it does duplicate the image on the second time just moves it to the second touches coordinates, then move on to 2, 3, 4, 5 as it should. any advice? or help to do this a better way? thanks

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  • Java me : Can we retrieve bluetooth address of connected device from an open slave connection ?

    - by Rohit
    Here is a typical sequence of events that occur : Host device opens a service ( Host device accepts and opens all incoming connections) A remote device connects to host device. Now, we have a slave connection open at host device. At host device, I want to know the bluetooth address of remote device. I can always pass it as data from remote to host device, but can I extract it from connection object somehow without any data transfer? Thanks in advance...

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  • Is it possible to use a serial port like session in c#?

    - by Pandiya Chendur
    I am using serial port communication in my asp.net webform application... private bool sendSMS(int portNo, string mobNo, string details) { try { SerialPort SerialPort1 = new SerialPort(); SerialPort1.PortName = "COM" + portNo.ToString(); SerialPort1.BaudRate = 9600; SerialPort1.Parity = Parity.None; SerialPort1.DataBits = 8; SerialPort1.StopBits = StopBits.One; SerialPort1.RtsEnable = true; SerialPort1.DtrEnable = true; SerialPort1.Encoding.GetEncoder(); SerialPort1.ReceivedBytesThreshold = 1; SerialPort1.NewLine = Environment.NewLine; SerialPort1.Open(); SerialPort1.Write("AT" + SerialPort1.NewLine); Sleep(500); SerialPort1.Write("AT+CMGF=1" + SerialPort1.NewLine); Sleep(500); SerialPort1.Write("AT+CMGS=" + (char)34 + mobNo + (char)34 + SerialPort1.NewLine); Sleep(1000); SerialPort1.Write(details + (char)26); Sleep(2000); SerialPort1.Close(); } catch { } return true; } This method works when i send i single message... But when want to send sms in bulk opening and closing port everytime is not a good idea... So my question is it possible to use a serial port like session in c#?... When i open a port i want it to be open for 1 hour and then if my time expires i want to close the port and open it the next time... Any suggestion...

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  • Linux Kernel - Integer to ASCII

    - by DRX-Z
    I need to convert an integer to it's ASCII representation from within the Linux Kernel. How can I do this? I can't find any built-in conversion methods. Are there any already in the kernel or do I need to add my own?

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  • Client/Server communication via internet

    - by user957829
    Hi, Which is the best solution to communicate bidirectionally between a remote server and a client behind an internet box? UPnP with Sockets. HTTPS/Database Server and the client make 1 request every Xsec to know if there is new data. Client opens 1 connection on the server and it maintains open to make a tunnel. Thanks in advance for your help

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  • Open source project. I want to participate in something

    - by user69514
    I am a senior in Computer Science. I want to be part of some open source project. I don't know what's available out there. Can anybody guide me? I'm good with Java, not that great with C and C++, but I know both. I also know some Cincom Smalltalk. Or if anyone has something good that they're working on I could help.

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  • Is there any interesting jobs available for C++ other than device drivers / firmwares developments?

    - by AKN
    Hi, Initially C was used for designing drivers / firmwares and all that. Right now this has been taken over by C++. Ok. Let me not deviate this question. I would like to know where else C++ is being used and how you see its future? You can also list out pros and cons of C++ compared to other languages. Would like to see a healthy and meaningful discussion on C++ current usage and its future?! Cheers! AKN

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