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  • Waiting for data via select not working

    - by BSchlinker
    I'm currently working on a project which involves multiple clients connected to a server and waiting for data. I'm using select and monitoring the connection for incoming data. However, the client just continues to print nothing, acting as if select has discovered incoming data. Perhaps I'm attacking this wrong? For the first piece of data the server does send, it is displayed correctly. However, the server then disconnects and the client continues to spew blank lines. FD_ZERO(&readnet); FD_SET(sockfd, &readnet); while(1){ rv = select(socketdescrip, &readnet, NULL, NULL, &timeout); if (rv == -1) { perror("select"); // error occurred in select() } else if (rv == 0) { printf("Connection timeout! No data after 10 seconds.\n"); } else { // one or both of the descriptors have data if (FD_ISSET(sockfd, &readnet)) { numbytes = recv(sockfd, buf, sizeof buf, 0); printf("Data Received\n"); buf[numbytes] = '\0'; printf("client: received '%s'\n",buf); sleep(10); } } }

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  • Generating a python file

    - by fema
    Hi! I'm havin issues with python (imo python itself is an issue). I have a txt file, it contains a custom language and I have to translate it to a working python code. The input: import sys n = int(sys.argv[1]) ;;print "Beginning of the program!" LOOP i in range(1,n) {print "The number:";;print i} BRANCH n < 5 {print n ;;print "less than 5"} The wanted output looks exactly like this: import sys n = int(sys.argv[1]) print "Beginning of the program!" for i in range(1,n) : print "The number:" print i if n < 5 : print n print "less than 5" The name of the input file is read from parameter. The out file is out.py. In case of a wrong parameter, it gives an error message. The ;; means a new line. When I tried to do it, I made an array, I read all the lines into it, split by " ". Then I wanted to strip it from the marks I don't need. I made 2 loops, one for the lines, one for the words. So then I started to replace the things. Everything went fine until it came to the } mark. It finds it, but it can not replace or strip it. I have no more idea what to do. Could someone help me, please? Thanks in advance!

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  • Does anyone else think instance variables are problematic in database-backed applications?

    - by Ben Aston
    It occurs to me that state control in languages like C# is not well supported. By this, I mean, it is left upto the programmer to manage the state of in-memory objects. A common use-case is that instance variables in the domain-model are copies of information residing in persistent storage (i.e. the database). Clearly this violates the single point of authority principle, and "synchronisation" has to be managed by the developer. I envisage a system where instead of instance variables, we have simple public access/mutator methods marked with attributes that link them to the database, and where reads and writes are mediated by a framework that decides whether to hit the database. Does such a system exist? Am I completely missing the point, or is there some truth to this idea?

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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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  • 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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  • .net 3.5 message framing

    - by Rob
    We have message framing working by using a lengh prefix but using .NET 2.0 beginSend/BeginReceive. Is message framing any different in 3.5, if so how should we implement it using the new framework? Are there any useable examples out there which focus purely on message framing using 3.5? Many thanks

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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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  • an error "variable of field declared void"

    - by lego69
    I have this code: header - test.h Inside header I have some class Z and definitions of two functions test and test2 I call function test2 from test void test2(Z z, Z const *za); this is implementation of the function: void test2(Z z, Z const *za){ int i = z; //this row works cout << i << endl; } I call it from test: test2(z1, za1); // za1 is pinter to object and z1 is some object but in my header I receive an 3 errors: Multiple markers at this line - initializer expression list treated as compound expression - `A' was not declared in this scope - variable or field `quiz2' declared void can somebody please explain why? thanks in advance

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  • HELP!! Implementing a search to match the specified author and displaying a book by the specified publisher

    - by Brian
    Hey guys! So i'm having problems with my assignment. I successfully got it to run multiple last names by the author, but now, I need to find all books by author, which means searching the collection for all books that match the specified author and I also need to find all books by publisher, which displays a list of books by the specified publisher. How would I implement this? Would I use string or vector? Any help will be much appreciated!

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  • Listening UDP or switch to TCP in a MFC application

    - by Alexander.S
    I'm editing a legacy MFC application, and I have to add some basic network functionalities. The operating side has to receive a simple instruction (numbers 1,2,3,4...) and do something based on that. The clients wants the latency to be as fast as possible, so naturally I decided to use datagrams (UDP). But reading all sorts of resources left me bugged. I cannot listen to UDP sockets (CAsyncSocket) in MFC, it's only possible to call Receive which blocks and waits. Blocking the UI isn't really a smart. So I guess I could use some threading technique, but since I'm not all that experienced with MFC how should that be implemented? The other part of the question is should I do this, or revert to TCP, considering reliability and implementation issues. I know that UDP is unreliable, but just how unreliable is it really? I read that it is up to 50% faster, which is a lot for me. References I used: http://msdn.microsoft.com/en-us/library/09dd1ycd(v=vs.80).aspx

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  • Detecting the Loopback Adapter

    - by BlueSkies
    What is the best way for detecting whether a network interface is a loopback adapter? The windows API's GetAdaptersInfo and GetAdaptersAddresses state in the documentation that they will return whether an interface is a loopback through the Type (MIB_IF_TYPE_LOOPBACK) but neither of these do for the Microsoft Loopback Adapter at least, it is reported as a standard ethernet interface. I could try checking for the default MAC of the Loopback adapter but this can be easily spoofed. I could check for the name "Microsoft Loopback Adapter" in the description but this may have translation issues and may lead to other issues. IP addresses can also be changed. What is the most robust method for doing this?

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  • What to Learn after C++?

    - by Stephen Whitmore
    I have been learning C++ for a while now, I find it very powerful. But, the problem is the the level of abstraction is not much and I have to do memory management myself. What are the languages that I can use which uses a higher level of abstraction.

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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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  • 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 to cast a character to int in Clojure?

    - by Learning Clojure
    How to cast a character to int in Clojure? I am trying to write a rot 13 in clojure, so I need to have something to cast my char to int. I found something called (int), so I put: (int a) Get: CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(NO_SOURCE_PATH:13:1) Then I put: (int 'a) Get: ClassCastException clojure.lang.Symbol cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) Then: (rot13 ''a') Get: ClassCastException clojure.lang.PersistentList cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) And: (rot13 "a") Get: ClassCastException java.lang.String cannot be cast to java.lang.Character clojure.lang.RT.intCast (RT.java:1087) So what is the right way to do it? btw, I always get confused with all these clojure syntax. But I can never find any source only help me with my problem. Any suggestions? Thank you!!

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