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  • List filtering: list comprehension vs. lambda + filter

    - by Agos
    I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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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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  • Using enum values to represent binary operators (or functions)

    - by Bears will eat you
    I'm looking for an elegant way to use values in a Java enum to represent operations or functions. My guess is, since this is Java, there just isn't going to be a nice way to do it, but here goes anyway. My enum looks something like this: public enum Operator { LT, LTEQ, EQEQ, GT, GTEQ, NEQ; ... } where LT means < (less than), LTEQ means <= (less than or equal to), etc - you get the idea. Now I want to actually use these enum values to apply an operator. I know I could do this just using a whole bunch of if-statements, but that's the ugly, OO way, e.g.: int a = ..., b = ...; Operator foo = ...; // one of the enum values if (foo == Operator.LT) { return a < b; } else if (foo == Operator.LTEQ) { return a <= b; } else if ... // etc What I'd like to be able to do is cut out this structure and use some sort of first-class function or even polymorphism, but I'm not really sure how. Something like: int a = ..., b = ...; Operator foo = ...; return foo.apply(a, b); or even int a = ..., b = ...; Operator foo = ...; return a foo.convertToOperator() b; But as far as I've seen, I don't think it's possible to return an operator or function (at least, not without using some 3rd-party library). Any suggestions?

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  • Having trouble getting GET variables from url.

    - by mchl
    Hey everyone, I'm having trouble with this algorithm to extract the get variables from a url and print them each on a new line like: x=y z=hello etc. but instead it prints a seemingly random section of the url with no newlines to the file. There must be a logic error of some kind but i just can't spot it. for(i_m=0;i_m<len_m;i_m++) { if(var_m[i_m]=='&') { fwrite(var_m+offset_m, 1, amp_m, echo_out); fputc('\n',echo_out); offset_m+=amp_m; amp_m=0; } amp_m++; } any help appreciated.

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  • C++0x implementation guesstimates?

    - by dsimcha
    The C++0x standard is on its way to being complete. Until now, I've dabbled in C++, but avoided learning it thoroughly because it seems like it's missing a lot of modern features that I've been spoiled by in other languages. However, I'd be very interested in C++0x, which addresses a lot of my complaints. Any guesstimates, after the standard is ratified, as to how long it will take for major compiler vendors to provide reasonably complete, production-quality implementations? Will it happen soon enough to reverse the decline in C++'s popularity, or is it too little, too late? Do you believe that C++0x will become "the C++" within a few years, or do you believe that most people will stick to the earlier standard in practice and C++0x will be somewhat of a bastard stepchild, kind of like C99?

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  • Cartesian Plane

    - by NuNu
    I'm trying to define a function in Haskell that takes an integer argument c and returns the list of all points on the cartesian plane of the form (x/c,y/c) where x and y are integers. x/c is between -2 and 1 and y/r is between -1 and 1 This is what I've gotten so far which I'm almost sure is right but I'm getting a parse error on input = when I run it particularly at this line: cart xs ys c = [(y/c,x/c) | x <- xs, y <- ys] plane :: Int -> [a] plane c = cart [-1*c .. 1*c] [-2*c .. 1*c] c cart xs ys c = [(y/c,x/c) | x <- xs, y <- ys] A sample output would be: plane 1 would generate: [(-2.0, -1.0), (-1.0, -1.0), ( 0.0, -1.0), ( 1.0, -1.0), (-2.0, 0.0), (-1.0, 0.0), ( 0.0, 0.0), ( 1.0, 0.0), (-2.0, 1.0), (-1.0, 1.0), ( 0.0, 1.0), ( 1.0, 1.0)] Anyone have any idea how I can fix this! Thanks

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  • Excelsheet query

    - by kunj
    Hi, Please tell me how can I find the last word from any particular cell in excel sheet if cell contains multiple words or instructions. For ex- The below string is in particular cell: C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Blue hills.jpg My requirement is to search only last word in that cell i.e. Blue hills.jpg Your early response is highly appreciated!!!

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  • wireless networks c program

    - by Nave
    i wud like to create a wireless network from a laptop. if some laptops come within this range, i wud like to send them a welcome message and when they leave the wifi range, i send them a bye message. is it possible to code such a thing in C? please help me out with this.

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  • error in script

    - by lego69
    can somebody please help, I'm working with C-Shell, I'm trying to run this script set callsTo = "`cut -d" " -f2 ${1}`" echo $callsTo cut receives data from the file which is the first parameter > ./myscript data I need only second field from every row -f2 after that I want to check if the data was stored, but I receive or an error unmatched `. or empty row, what is wrong with my script, thanks in advance for any help

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  • Windows service: Listening on socket while running as LocalSystem

    - by Socob
    I'm writing a small server-like program in C for Windows (using MinGW/GCC, testing on Windows 7) which is eventually supposed to run as a service with the LocalSystem account. I am creating a socket, and using Windows Sockets bind(), listen() and accept() to listen for incoming connections. If I run the application from the command line (i.e. not as a service, but as a normal user), I have no problems connecting to it from external IPs. However, if I run the program as a service with the LocalSystem account, I can only connect to the service from my own PC, either with 127.0.0.1 or my local address, 192.168.1.80 (I'm behind a router in a small local network). Neither external IPs nor other PCs in the same local network, using my local address, can connect now, even though there were no problems without running as a service. Now, I've heard that networking is handled differently or even not accessible (?) when running as LocalSystem or LocalService or that services cannot access both the desktop and the network (note: my service is not interactive) at the same time due to security considerations. Essentially, I need to find out what's going wrong/how to listen for connections in a service. Is running as NetworkService the same as running as LocalSystem, but with network access? Surely there must be servers that can run as background services, so how do they do it?

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  • where to find "template" interfaces?

    - by fayer
    i wonder where one can find template interfaces. eg. i am creating these classes that implements iLog: DatabaseLog ScreenLog FileLog i wonder what methods should a typical Log class have? is there a set of interfaces you could just implement/learn from rather than reinvent the wheel and have to think about the method names. eg. Interfaces: iLog iDatabase iErrorMessage etc. Thanks

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  • Wake up thread blocked on accept() call

    - by selbie
    Sockets on Linux question I have a worker thread that is blocked on an accept() call. It simply waits for an incoming network connection, handles it, and then returns to listening for the next connection. When it is time for the program to exit, how do I signal this network worker thread (from the main thread) to return from the accept() call while still being able to gracefully exit its loop and handle it's cleanup code. Some things I tried: 1. pthread_kill to send a signal. Feels kludgy to do this, plus it doesn't reliably allow the thread to do it's shutdown logic. Also makes the program terminate as well. I'd like to avoid signals if at all possible. pthread_cancel. Same as above. It's a harsh kill on the thread. That, and the thread may be doing something else. Closing the listen socket from the main thread in order to make accept() abort. This doesn't reliably work. Some constraints: If the solution involves making the listen socket non-blocking, that is fine. But I don't want to accept a solution that involves the thread waking up via a select call every few seconds to check the exit condition. The thread condition to exit may not be tied to the process exiting. Essentially, the logic I am going for looks like this. void* WorkerThread(void* args) { DoSomeImportantInitialization(); // initialize listen socket and some thread specific stuff while (HasExitConditionBeenSet()==false) { listensize = sizeof(listenaddr); int sock = accept(listensocket, &listenaddr, &listensize); // check if exit condition has been set using thread safe semantics if (HasExitConditionBeenSet()) { break; } if (sock < 0) { printf("accept returned %d (errno==%d)\n", sock, errno); } else { HandleNewNetworkCondition(sock, &listenaddr); } } DoSomeImportantCleanup(); // close listen socket, close connections, cleanup etc.. return NULL; } void SignalHandler(int sig) { printf("Caught CTRL-C\n"); } void NotifyWorkerThreadToExit(pthread_t thread_handle) { // signal thread to exit } int main() { void* ptr_ret= NULL; pthread_t workerthread_handle = 0; pthread_create(&workerthread, NULL, WorkerThread, NULL); signal(SIGINT, SignalHandler); sleep((unsigned int)-1); // sleep until the user hits ctrl-c printf("Returned from sleep call...\n"); SetThreadExitCondition(); // sets global variable with barrier that worker thread checks on // this is the function I'm stalled on writing NotifyWorkerThreadToExit(workerthread_handle); // wait for thread to exit cleanly pthread_join(workerthread_handle, &ptr_ret); DoProcessCleanupStuff(); }

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  • how to access child instances in a vector in c++

    - by tsubasa
    I have a parent class and child class (inherited from parent). In the child class, I have a member function named function_blah(); I used vector<parent*> A to store 5 parent instances, 3 child instances. So the total number of elements in the vector is 8. I can easily access to member functions of element A[0] to A[4], which are parent instances. But whenever I try to have access to member functions of element A[5] to A[7], the compiler complains that class parent has no member named 'function_blah' The way I access to elements is using index. e.x A[i] with i = 0..7. Is it correct? if not, how?

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  • what is main focus for a developer when coding?

    - by ajsie
    i read a lot of books about how to code right and usually the are talking about all these techniques from a point of view i can't understand. eg. lets consider the singleton pattern. i'm restricting so the class can only be instantiated once. but since it's only me creating the application, if i know that the class only should be instantiated once, then why would i create it a second time? i feel like missing the big picture. what is my main goal when coding an application? how should i think? thanks

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  • How can I programmatically get the connection status of OSX network services?

    - by BigBrainz
    In the OS X System Preferences, when I click on 'Network' I see a green dot by 'Ethernet', and red dots by 'AirPort' and 'FireWire'. This is because I turned off AirPort and FireWire, as I access networks and the Internet via Ethernet. I need to programmatically determine which of these network services displayed in System Preferences have green dots and which have red dots. For Ethernet and FireWire the displayed status is 'Connected' or 'Not Connected', and for AirPort the displayed status is 'On' or 'Off'. Perhaps other network services have other status labels. I have picked through all the plist files in '/Library/Preferences/SystemConfiguration', particularly 'preferences.plist' and 'NetworkInterfaces.plist'. I can get all sorts of information there, such as the Location set, network service order, proxy information (which is also important to my task), but I cannot find how to determine whether a given network service is on or off--the equivalent of having the green dot displayed. I have also tried using System Configuration framework, specifically the SCNetworkConnectionGetStatus function, but all I get are invalid connection statuses. Does anyone know how to actually retrieve this connection status information? Thanks.

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