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  • Is it faster to count down than it is to count up?

    - by Bob
    Our computer science teacher once said that for some reason it is more efficient to count down that count up. For example if you need to use a FOR loop and the loop index is not used somewhere (like printing a line of N * to the screen) I mean that code like this : for (i=N; i>=0; i--) putchar('*'); is better than: for (i=0; i<N; i++) putchar('*'); Is it really true? and if so does anyone know why?

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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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  • Design for fastest page download

    - by mexxican
    I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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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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  • 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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  • What's the *right* way to handle a POST in FP?

    - by Malvolio
    I'm just getting started with FP and I'm using Scala, which may not be the best way, since I can always fall back to an imperative style if the going gets tough. I'd just rather not. I've got a very specific question that points to a broader lacuna in my understanding of FP. When a web application is processing a GET request, the user wants information that already exists on the web-site. The application only has to process and format the data in some way. The FB way is clear. When a web application is processing a POST request, the user wants change the information held on the site. True, the information is not typically held in application variables, it's in a database or a flat-file, but still, I get the feeling I'm not grokking FP properly. Is there a pattern for handling updates to static data in an FP language? My vague picture of this is that the application is handed the request and the then-current site state. The application does its thing and returns the new site-state. If the current site-state hasn't changed since the application started, the new state becomes the current state and the reply is sent back to the browser (this is my dim image of Clojure's style); if the current state has been changed (by another thread, well, something else happens ...

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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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  • 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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  • 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 filter and intercept Linux packets by using net_dev_add() API?

    - by Khajavi
    I'm writing ethernet network driver for linux. I want to receive packets, edit and resend them. I know how to edit the packet in packet_interceptor function, but how can I drop incoming packets in this function?? #include <linux/netdevice.h> #include <linux/skbuff.h> #include <linux/ip.h> #include <net/sock.h> struct packet_type my_proto; int packet_interceptor(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { // I dont want certain packets go to upper in net_devices for further processing. // How can I drop sk_buff here?! return 0; } static int hello_init( void ) { printk(KERN_INFO "Hello, world!\n"); my_proto.type = htons(ETH_P_ALL); my_proto.dev = NULL; my_proto.func = packet_interceptor; dev_add_pack(&my_proto); return 0; } static void hello_exit(void) { dev_remove_pack(&my_proto); printk(KERN_INFO "Bye, world\n"); } module_init(hello_init); module_exit(hello_exit);

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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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  • Can anyone help me find why this C program work on VS2005 but not on DEV-C++

    - by user333771
    Hello to everybody..and greetings from Greece I have a C program for an exercise and it has a strange issue The program runs just fine on VS 2005 but it crashes on DEV-C++ and the problem that the problem is that the exercise is always evaluated against DEV-C++ The program is about inserting nodes to a BST and this is where the problem lies... Well i would really appreciate some help. enter code here #include <stdio.h> #include <stdlib.h> #include <malloc.h> typedef struct tree_node { int value; int weight; struct tree_node *left; struct tree_node *right; } TREE_NODE; /* The Following function creates a Binary Search Treed */ TREE_NODE *create_tree(int list[], int size); TREE_NODE *search_pos_to_insert(TREE_NODE *root, int value, int *left_or_right); /* this is the problematic function */ void inorder(TREE_NODE *root); /* Inorder Traversing */ TREE_NODE *temp; int main() { TREE_NODE *root; /* Pointer to the root of the BST */ int values[] = {10, 5, 3, 4, 1, 9, 6, 7, 8, 2}; /* Values for BST */ int size = 10, tree_weight; root = create_tree(values, 10); printf("\n"); inorder(root); /* Inorder BST*/ system("PAUSE"); } TREE_NODE *search_pos_to_insert(TREE_NODE *root, int value, int *left_or_right) { if(root !=NULL) { temp = root; if(value >root->value) { *left_or_right=1; *search_pos_to_insert(root->right, value, left_or_right); } else { *left_or_right=0; *search_pos_to_insert(root->left, value, left_or_right); } } else return temp;/* THIS IS THE PROBLEM (1) */ } TREE_NODE *create_tree(int list[], int size) { TREE_NODE *new_node_pntr, *insert_point, *root = NULL; int i, left_or_right; /* First Value of the Array is the root of the BST */ new_node_pntr = (TREE_NODE *) malloc(sizeof(TREE_NODE)); new_node_pntr->value = list[0]; /* ¸íèåóå ôçí ðñþôç ôéìÞ ôïõ ðßíáêá. */ new_node_pntr->weight = 0; new_node_pntr->left = NULL; new_node_pntr->right = NULL; root = new_node_pntr; /* Now the rest of the arrat. */ for (i = 1; i < size; i++) { insert_point = search_pos_to_insert(root, list[i], &left_or_right); /* THIS IS THE PROBLEM (2) */ /* insert_point just won't get the return from temp */ new_node_pntr = (TREE_NODE *) malloc(sizeof(TREE_NODE)); new_node_pntr->value = list[i]; new_node_pntr->weight = 0; new_node_pntr->left = NULL; new_node_pntr->right = NULL; if (left_or_right == 0) insert_point->left = new_node_pntr; else insert_point->right = new_node_pntr; } return(root); } void inorder(TREE_NODE *root) { if (root == NULL) return; inorder(root->left); printf("Value: %d, Weight: %d.\n", root->value, root->weight); inorder(root->right); }

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  • Haskell: Why is it saying my function type is off?

    - by linkmaster03
    I wrote a little Haskell program to find the area of a triangle, primarily to practice custom types, but it keeps throwing the following error on compile: areafinder.hs:7:4: Couldn't match expected type 'Triangle' against inferred type 'm b' In a stmt of a 'do' expression: putStr "Base: " In the expression: do { putStr "Base: "; baseStr I'm not sure where 'm b' comes from, so I'm at a loss here. Why is it throwing this error, and what can I do to fix it? Here is my code: module Main where data Triangle = Triangle Double Double -- base, height getTriangle :: Triangle getTriangle = do putStr "Base: " baseStr Double calcTriangle (Triangle base height) = base * height main = putStrLn ("Area = " ++ show (calcTriangle getTriangle)) 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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  • 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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  • 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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  • 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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