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• Wifi hotspot disconnected after some time

  - by Rohit Bansal

  I am trying to use my Ubuntu system as Wifi Hotspot, but for some reason Hotspot get disconnected on its own. Searching for the solution, I found this help : Why is my ethernet connection connecting and disconnecting repeatedly? Reading through the above article I used the following command sudo killall dnsmasq as a result I manage to establish hotspot for around 5-10 sec before getting disconnected as against immediately.... Here's the system log (in case needed) tail -f /var/log/syslog : Apr 1 23:31:42 NetworkManager[901]: <info> Starting dnsmasq... Apr 1 23:31:42 NetworkManager[901]: <info> (wlan0): device state change: ip-config -> activated (reason 'none') [70 100 0] Apr 1 23:31:42 dnsmasq[4159]: started, version 2.57 cachesize 150 Apr 1 23:31:42 dnsmasq[4159]: compile time options: IPv6 GNU-getopt DBus I18N DHCP TFTP IDN Apr 1 23:31:42 dnsmasq-dhcp[4159]: DHCP, IP range 10.42.43.10 -- 10.42.43.100, lease time 1h Apr 1 23:31:42 dnsmasq[4159]: reading /etc/resolv.conf Apr 1 23:31:42 dnsmasq[4159]: using nameserver 220.226.6.104#53 Apr 1 23:31:42 dnsmasq[4159]: using nameserver 220.226.100.40#53 Apr 1 23:31:42 dnsmasq[4159]: cleared cache Apr 1 23:31:42 NetworkManager[901]: <info> Activation (wlan0) successful, device activated. Apr 1 23:31:42 NetworkManager[901]: <info> Activation (wlan0) Stage 5 of 5 (IP Configure Commit) complete. Apr 1 23:31:42 NetworkManager[901]: <info> Activation (wlan0) Stage 4 of 5 (IP4 Configure Get) complete. Apr 1 23:31:42 dbus[885]: [system] Activating service name='org.freedesktop.nm_dispatcher' (using servicehelper) Apr 1 23:31:42 dbus[885]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher' Connection established at this point....now disconnecting after 10 sec... Apr 1 23:31:52 ntpdate[4194]: adjust time server 91.189.94.4 offset -0.011589 sec Apr 1 23:32:01 NetworkManager[901]: <info> (wlan0): IP6 addrconf timed out or failed. Apr 1 23:32:01 NetworkManager[901]: <info> Activation (wlan0) Stage 4 of 5 (IP6 Configure Timeout) scheduled... Apr 1 23:32:01 NetworkManager[901]: <info> Activation (wlan0) Stage 4 of 5 (IP6 Configure Timeout) started... Apr 1 23:32:01 NetworkManager[901]: <info> Activation (wlan0) Stage 5 of 5 (IP Configure Commit) started... Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol tcp --destination-port 53 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol udp --destination-port 53 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol tcp --destination-port 67 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol udp --destination-port 67 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --in-interface wlan0 --jump REJECT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --out-interface wlan0 --jump REJECT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --in-interface wlan0 --out-interface wlan0 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --source 10.42.43.0/255.255.255.0 --in-interface wlan0 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --destination 10.42.43.0/255.255.255.0 --out-interface wlan0 --match state --state ESTABLISHED,RELATED --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table nat --insert POSTROUTING --source 10.42.43.0/255.255.255.0 ! --destination 10.42.43.0/255.255.255.0 --jump MASQUERADE Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol tcp --destination-port 53 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol udp --destination-port 53 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol tcp --destination-port 67 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert INPUT --in-interface wlan0 --protocol udp --destination-port 67 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --in-interface wlan0 --jump REJECT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --out-interface wlan0 --jump REJECT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --in-interface wlan0 --out-interface wlan0 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --source 10.42.43.0/255.255.255.0 --in-interface wlan0 --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --destination 10.42.43.0/255.255.255.0 --out-interface wlan0 --match state --state ESTABLISHED,RELATED --jump ACCEPT Apr 1 23:32:01 NetworkManager[901]: <info> Executing: /sbin/iptables --table nat --insert POSTROUTING --source 10.42.43.0/255.255.255.0 ! --destination 10.42.43.0/255.255.255.0 --jump MASQUERADE Apr 1 23:32:01 NetworkManager[901]: <info> Starting dnsmasq... Apr 1 23:32:01 NetworkManager[901]: <info> Activation (wlan0) Stage 5 of 5 (IP Configure Commit) complete. Apr 1 23:32:01 NetworkManager[901]: <info> Activation (wlan0) Stage 4 of 5 (IP6 Configure Timeout) complete. Apr 1 23:32:01 NetworkManager[901]: <warn> dnsmasq died with signal 9 Apr 1 23:32:01 NetworkManager[901]: <info> (wlan0): device state change: activated -> failed (reason 'sharing-start-failed') [100 120 18] Apr 1 23:32:01 dnsmasq[4235]: started, version 2.57 cachesize 150 Apr 1 23:32:01 dnsmasq[4235]: compile time options: IPv6 GNU-getopt DBus I18N DHCP TFTP IDN Apr 1 23:32:01 dnsmasq-dhcp[4235]: DHCP, IP range 10.42.43.10 -- 10.42.43.100, lease time 1h Apr 1 23:32:01 NetworkManager[901]: <warn> Activation (wlan0) failed for access point (Reppify Ubuntu) Apr 1 23:32:01 dnsmasq[4235]: reading /etc/resolv.conf Apr 1 23:32:01 dnsmasq[4235]: using nameserver 220.226.6.104#53 Apr 1 23:32:01 dnsmasq[4235]: using nameserver 220.226.100.40#53 Apr 1 23:32:01 dnsmasq[4235]: cleared cache Apr 1 23:32:01 NetworkManager[901]: <warn> Activation (wlan0) failed. Apr 1 23:32:01 NetworkManager[901]: <info> (wlan0): device state change: failed -> disconnected (reason 'none') [120 30 0] Apr 1 23:32:01 NetworkManager[901]: <info> (wlan0): deactivating device (reason 'none') [0] Apr 1 23:32:01 dbus[885]: [system] Activating service name='org.freedesktop.nm_dispatcher' (using servicehelper) Apr 1 23:32:01 dbus[885]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher' Apr 1 23:32:01 NetworkManager[901]: <error> [1333303321.565351] [nm-device-wifi.c:1815] nm_device_wifi_set_mode(): (wlan0): error setting mode 2

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• Lawler's Algorithm Implementation Assistance

  - by Richard Knop

  Here is my implemenation of Lawler's algorithm in PHP (I know... but I'm used to it): <?php $jobs = array(1, 2, 3, 4, 5, 6); $jobsSubset = array(2, 5, 6); $n = count($jobs); $processingTimes = array(2, 3, 4, 3, 2, 1); $dueDates = array(3, 15, 9, 7, 11, 20); $optimalSchedule = array(); foreach ($jobs as $j) { $optimalSchedule[] = 0; } $dicreasedCardinality = array(); for ($i = $n; $i >= 1; $i--) { $x = 0; $max = 0; // loop through all jobs for ($j = 0; $j < $i; $j++) { // ignore if $j already is in the $dicreasedCardinality array if (false === in_array($j, $dicreasedCardinality)) { // if the job has no succesor in $jobsSubset if (false === isset($jobs[$j+1]) || false === in_array($jobs[$j+1], $jobsSubset)) { // here I find an array index of a job with the maximum due date // amongst jobs with no sucessor in $jobsSubset if ($x < $dueDates[$j]) { $x = $dueDates[$j]; $max = $j; } } } } // move the job at the end of $optimalSchedule $optimalSchedule[$i-1] = $jobs[$max]; // decrease the cardinality of $jobs $dicreasedCardinality[] = $max; } print_r($optimalSchedule); Now the above returns an optimal schedule like this: Array ( [0] => 1 [1] => 1 [2] => 1 [3] => 3 [4] => 2 [5] => 6 ) Which doesn't seem right to me. The problem might be with my implementation of the algorithm because I am not sure I understand it correctly. I used this source to implement it: http://www.google.com/books?id=aSiBs6PDm9AC&pg=PA166&dq=lawler%27s+algorithm+code&lr=&hl=sk&cd=4#v=onepage&q=&f=false The description there is a little confusing. For example, I didn't quite get how is the subset D defined (I guess it is arbitrary). Could anyone help me out with this? I have been trying to find some sources with simpler explanation of the algorithm but all sources I found were even more complicated (with math proofs and such) so I am stuck with the link above. Yes, this is a homework, if it wasn't obvious. I still have few weeks to crack this but I have spent few days already trying to get how exactly this algorithm works with no success so I don't think I will get any brighter during that time.

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• Is this (Lock-Free) Queue Implementation Thread-Safe?

  - by Hosam Aly

  I am trying to create a lock-free queue implementation in Java, mainly for personal learning. The queue should be a general one, allowing any number of readers and/or writers concurrently. Would you please review it, and suggest any improvements/issues you find? Thank you. import java.util.concurrent.atomic.AtomicReference; public class LockFreeQueue<T> { private static class Node<E> { E value; volatile Node<E> next; Node(E value) { this.value = value; } } private AtomicReference<Node<T>> head, tail; public LockFreeQueue() { // have both head and tail point to a dummy node Node<T> dummyNode = new Node<T>(null); head = new AtomicReference<Node<T>>(dummyNode); tail = new AtomicReference<Node<T>>(dummyNode); } /** * Puts an object at the end of the queue. */ public void putObject(T value) { Node<T> newNode = new Node<T>(value); Node<T> prevTailNode = tail.getAndSet(newNode); prevTailNode.next = newNode; } /** * Gets an object from the beginning of the queue. The object is removed * from the queue. If there are no objects in the queue, returns null. */ public T getObject() { Node<T> headNode, valueNode; // move head node to the next node using atomic semantics // as long as next node is not null do { headNode = head.get(); valueNode = headNode.next; // try until the whole loop executes pseudo-atomically // (i.e. unaffected by modifications done by other threads) } while (valueNode != null && !head.compareAndSet(headNode, valueNode)); T value = (valueNode != null ? valueNode.value : null); // release the value pointed to by head, keeping the head node dummy if (valueNode != null) valueNode.value = null; return value; }

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• Is this good code? Linked List Stack Implementation

  - by Quik Tester

  I have used the following code for a stack implementation. The top keeps track of the topmost node of the stack. Now since top is a data member of the node function, each node created will have a top member, which ideally we wouldn't want. Firstly, is this good approach to coding? Secondly, will making top as static make it a better coding practice? Or should I have a global declaration of top? #include<iostream> using namespace std; class node { int data; node *top; node *link; public: node() { top=NULL; link=NULL; } void push(int x) { node *n=new node; n->data=x; n->link=top; top=n; cout<<"Pushed "<<n->data<<endl; } void pop() { node *n=new node; n=top; top=top->link; n->link=NULL; cout<<"Popped "<<n->data<<endl; delete n; } void print() { node *n=new node; n=top; while(n!=NULL) { cout<<n->data<<endl; n=n->link; } delete n; } }; int main() { node stack; stack.push(5); stack.push(7); stack.push(9); stack.pop(); stack.print(); } Any other suggestions welcome. I have also seen codes where there are two classes, where the second one has the top member. What about this? Thanks. :)

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• Oracle Coding Standards Feature Implementation

  - by Mike Hofer

  Okay, I have reached a sort of an impasse. In my open source project, a .NET-based Oracle database browser, I've implemented a bunch of refactoring tools. So far, so good. The one feature I was really hoping to implement was a big "Global Reformat" that would make the code (scripts, functions, procedures, packages, views, etc.) standards compliant. (I've always been saddened by the lack of decent SQL refactoring tools, and wanted to do something about it.) Unfortunatey, I am discovering, much to my chagrin, that there doesn't seem to be any one widely-used or even "generally accepted" standard for PL-SQL. That kind of puts a crimp on my implementation plans. My search has been fairly exhaustive. I've found lots of conflicting documents, threads and articles and the opinions are fairly diverse. (Comma placement, of all things, seems to generate quite a bit of debate.) So I'm faced with a couple of options: Add a feature that lets the user customize the standard and then reformat the code according to that standard. —OR— Add a feature that lets the user customize the standard and simply generate a violations list like StyleCop does, leaving the SQL untouched. In my mind, the first option saves the end-users a lot of work, but runs the risk of modifying SQL in potentially unwanted ways. The second option runs the risk of generating lots of warnings and doing no work whatsoever. (It'd just be generally annoying.) In either scenario, I still have no standard to go by. What I'd need to know from you guys is kind of poll-ish, but kind of not. If you were going to use a tool of this nature, what parts of your SQL code would you want it to warn you about or fix? Again, I'm just at a loss due to a lack of a cohesive standard. And given that there isn't anything out there that's officially published by Oracle, I think this is something the community could weigh in on. Also, given the way that voting works on SO, the votes would help to establish the popularity of a given "refactoring." P.S. The engine parses SQL into an expression tree so it can robustly analyze the SQL and reformat it. There should be quite a bit that we can do to correct the format of the SQL. But I am thinking that for the first release of the thing, layout is the primary concern. Though it is worth noting that the thing already has refactorings for converting keywords to upper case, and identifiers to lower case.

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• C# Property Access vs Interface Implementation

  - by ehdv

  I'm writing a class to represent a Pivot Collection, the root object recognized by Pivot. A Collection has several attributes, a list of facet categories (each represented by a FacetCategory object) and a list of items (each represented by a PivotItem object). Therefore, an extremely simplified Collection reads: public class Collection { private List<FacetCategory> categories; private List<PivotItem> items; // other attributes } What I'm unsure of is how to properly grant access to those two lists. Because declaration order of both facet categories and items is visible to the user, I can't use sets, but the class also shouldn't allow duplicate categories or items. Furthermore, I'd like to make the Collection object as easy to use as possible. So my choices are: Have Collection implement IList<PivotItem> and have accessor methods for FacetCategory: In this case, one would add an item to Collection foo by writing foo.Add(bar). This works, but since a Collection is equally both kinds of list making it only pass as a list for one type (category or item) seems like a subpar solution. Create nested wrapper classes for List (CategoryList and ItemList). This has the advantage of making a consistent interface but the downside is that these properties would no longer be able to serve as lists (because I need to override the non-virtual Add method I have to implement IList rather than subclass List. Implicit casting wouldn't work because that would return the Add method to its normal behavior. Also, for reasons I can't figure out, IList is missing an AddRange method... public class Collection { private class CategoryList: IList<FacetCategory> { // ... } private readonly CategoryList categories = new CategoryList(); private readonly ItemList items = new ItemList(); public CategoryList FacetCategories { get { return categories; } set { categories.Clear(); categories.AddRange(value); } } public ItemList Items { get { return items; } set { items.Clear(); items.AddRange(value); } } } Finally, the third option is to combine options one and two, so that Collection implements IList<PivotItem> and has a property FacetCategories. Question: Which of these three is most appropriate, and why?

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• Is this implementation truely tail-recursive?

  - by CFP

  Hello everyone! I've come up with the following code to compute in a tail-recursive way the result of an expression such as 3 4 * 1 + cos 8 * (aka 8*cos(1+(3*4))) The code is in OCaml. I'm using a list refto emulate a stack. type token = Num of float | Fun of (float->float) | Op of (float->float->float);; let pop l = let top = (List.hd !l) in l := List.tl (!l); top;; let push x l = l := (x::!l);; let empty l = (l = []);; let pile = ref [];; let eval data = let stack = ref data in let rec _eval cont = match (pop stack) with | Num(n) -> cont n; | Fun(f) -> _eval (fun x -> cont (f x)); | Op(op) -> _eval (fun x -> cont (op x (_eval (fun y->y)))); in _eval (fun x->x) ;; eval [Fun(fun x -> x**2.); Op(fun x y -> x+.y); Num(1.); Num(3.)];; I've used continuations to ensure tail-recursion, but since my stack implements some sort of a tree, and therefore provides quite a bad interface to what should be handled as a disjoint union type, the call to my function to evaluate the left branch with an identity continuation somehow irks a little. Yet it's working perfectly, but I have the feeling than in calling the _eval (fun y->y) bit, there must be something wrong happening, since it doesn't seem that this call can replace the previous one in the stack structure... Am I misunderstanding something here? I mean, I understand that with only the first call to _eval there wouldn't be any problem optimizing the calls, but here it seems to me that evaluation the _eval (fun y->y) will require to be stacked up, and therefore will fill the stack, possibly leading to an overflow... Thanks!

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• log4bash: Cannot find a way to add MaxBackupIndex to this logger implementation

  - by Syffys

  I have been trying to modify this log4bash implementation but I cannot manage to make it work. Here's a sample: #!/bin/bash TRUE=1 FALSE=0 ############### Added for testing log4bash_LOG_ENABLED=$TRUE log4bash_rootLogger=$TRACE,f,s log4bash_appender_f=file log4bash_appender_f_dir=$(pwd) log4bash_appender_f_file=test.log log4bash_appender_f_roll_format=%Y%m log4bash_appender_f_roll=$TRUE log4bash_appender_f_maxBackupIndex=10 #################################### log4bash_abs(){ if [ "${1:0:1}" == "." ]; then builtin echo ${rootDir}/${1} else builtin echo ${1} fi } log4bash_check_app_dir(){ if [ "$log4bash_LOG_ENABLED" -eq $TRUE ]; then dir=$(log4bash_abs $1) if [ ! -d ${dir} ]; then #log a seperation line mkdir $dir fi fi } # Delete old log files # $1 Log directory # $2 Log filename # $3 Log filename suffix # $4 Max backup index log4bash_delete_old_files(){ ##### Added for testing builtin echo "Running log4bash_delete_old_files $@" &2 ##### if [ "$log4bash_LOG_ENABLED" -eq $TRUE ] && [ -n "$3" ] && [ "$4" -gt 0 ]; then local directory=$(log4bash_abs $1) local filename=$2 local maxBackupIndex=$4 local suffix=$(echo "${3}" | sed -re 's/[^.]/?/g') local logFileList=$(find "${directory}" -mindepth 1 -maxdepth 1 -name "${filename}${suffix}" -type f | xargs ls -1rt) local fileCnt=$(builtin echo -e "${logFileList}" | wc -l) local fileToDeleteCnt=$(($fileCnt-$maxBackupIndex)) local fileToDelete=($(builtin echo -e "${logFileList}" | head -n "${fileToDeleteCnt}" | sed ':a;N;$!ba;s/\n/ /g')) ##### Added for testing builtin echo "log4bash_delete_old_files About to start deletion ${fileToDelete[@]}" &2 ##### if [ ${fileToDeleteCnt} -gt 0 ]; then for f in "${fileToDelete[@]}"; do #### Added for testing builtin echo "Removing file ${f}" &2 #### builtin eval rm -f ${f} done fi fi } #Appender # $1 Log directory # $2 Log file # $3 Log file roll ? # $4 Appender Name log4bash_filename(){ builtin echo "Running log4bash_filename $@" &2 local format local filename log4bash_check_app_dir "${1}" if [ ${3} -eq 1 ];then local formatProp=${4}_roll_format format=${!formatProp} if [ -z ${format} ]; then format=$log4bash_appender_file_format fi local suffix=.`date "+${format}"` filename=${1}/${2}${suffix} # Old log files deletion local previousFilenameVar=int_${4}_file_previous local maxBackupIndexVar=${4}_maxBackupIndex if [ -n "${!maxBackupIndexVar}" ] && [ "${!previousFilenameVar}" != "${filename}" ]; then builtin eval export $previousFilenameVar=$filename log4bash_delete_old_files "${1}" "${2}" "${suffix}" "${!maxBackupIndexVar}" else builtin echo "log4bash_filename $previousFilenameVar = ${!previousFilenameVar}" fi else filename=${1}/${2} fi builtin echo $filename } ######################## Added for testing filename_caller(){ builtin echo "filename_caller Call $1" output=$(log4bash_abs $(log4bash_filename "${log4bash_appender_f_dir}" "${log4bash_appender_f_file}" "1" "log4bash_appender_f" )) builtin echo ${output} } #### Previous logs generation for i in {1101..1120}; do file="${log4bash_appender_f_file}.2012${i:2:3}" builtin echo "${file} $i" touch -m -t "2012${i}0000" ${log4bash_appender_f_dir}/$file done for i in {1..4}; do filename_caller $i done I expect log4bash_filename function to step into the following if only when the calculated log filename is different from the previous one: if [ -n "${!maxBackupIndexVar}" ] && [ "${!previousFilenameVar}" != "${filename}" ]; then For this scenario to apply, I'd need ${!previousFilenameVar} to be correctly set, but it's not the case, so log4bash_filename steps into this if all the time which is really not necessary... It looks like the issue is due to the following line not working properly: builtin eval export $previousFilenameVar=$filename I have a some theories to explain why: in the original code, functions are declared and exported as readonly which makes them unable to modify global variable. I removed readonly declarations in the above sample, but probleme persists. Function calls are performed in $() which should make them run into seperated shell instances so variable modified are not exported to the main shell But I cannot manage to find a workaround to this issue... Any help is appreciated, thanks in advance!

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• Conceptual inheritance implementation

  - by TheSENDER

  Hi there, I'm writing a spatial data structure and I have a doubt about what's the best NODE implementation. According to my design I have an abstract node entity and three classes which inherit from it: EMPTYNODE, FULLNODE, INTERNALNODE. The first one has no particular data. The second one has 1 reference to a generic element. The third one has 2 references to other nodes. I have found several ways to implement this situation (that I have already coded) but I can't decide what's the best. The first solution that I have found is to use a single class Node that potentially performs all the operation in this way: private static class Node { private Elem elem = null; private Node left = null, right = null; public Elem getElem() { assert isFull(); return elem; } public boolean isEmpty() { return elem == null && left == null; } public boolean isFull() { return elem != null; } public boolean isInternal() { return elem == null && left != null; } } The second solution is to write an explicit division by classes where every class offers only its methods. Obviously in this way we are obliged to perform several casts to the node objects. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); } private static class FullNode extends Node{ private ITriangle elem; @Override public boolean isEmpty() { return false; } @Override public final boolean isFull() { return true; } @Override public final boolean isInternal() { return false; } public Elem getElem() { return elem; } } The third one solution is to use the inheritance allowing every classes to offer all the methods, but the object type should by check by "isEmpty()" and similar methods. In case of wrong call we'll throw an exception. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); public abstract Elem getElem(); } private static class Empty extends Node{ @Override public boolean isEmpty() { return true; } @Override public final boolean isFull() { return false; } @Override public final boolean isInternal() { return false; } @Override public Elem getElem() { throw new AssertionError(); } } What do you think about these three solutions? Which one would you use? Any other ideas? Thanks for your help. Every idea will be appreciated.

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• c++ template function compiles in header but not implementation

  - by flies

  I'm trying to learn templates and I've run into this confounding error. I'm declaring some functions in a header file and I want to make a separate implementation file where the functions will be defined. Here's the code that calls the header (dum.cpp): #include <iostream> #include <vector> #include <string> #include "dumper2.h" int main() { std::vector<int> v; for (int i=0; i<10; i++) { v.push_back(i); } test(); std::string s = ", "; dumpVector(v,s); } now, here's a working header file (dumper2.h): #include <iostream> #include <string> #include <vector> void test(); template <class T> void dumpVector( std::vector<T> v,std::string sep); template <class T> void dumpVector(std::vector<T> v, std::string sep) { typename std::vector<T>::iterator vi; vi = v.begin(); std::cout << *vi; vi++; for (;vi<v.end();vi++) { std::cout << sep << *vi ; } std::cout << "\n"; return; } with implentation (dumper2.cpp): #include <iostream> #include "dumper2.h" void test() { std::cout << "!olleh dlrow\n"; } the weird thing is that if I move the code that defines dumpVector from the .h to the .cpp file, I get the following error: g++ -c dumper2.cpp -Wall -Wno-deprecated g++ dum.cpp -o dum dumper2.o -Wall -Wno-deprecated /tmp/ccKD2e3G.o: In function `main': dum.cpp:(.text+0xce): undefined reference to `void dumpVector<int>(std::vector<int, std::allocator<int> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)' collect2: ld returned 1 exit status make: *** [dum] Error 1 So why does it work one way and not the other? Clearly the compiler can find test(), so why can't it find dumpVector?

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• Tips on creating user interfaces and optimizing the user experience

  - by Saif Bechan

  I am currently working on a project where a lot of user interaction is going to take place. There is also a commercial side as people can buy certain items and services. In my opinion a good blend of user interface, speed and security is essential for these types of websites. It is fairly easy to use ajax and JavaScript nowadays to do almost everything, as there are a lot of libraries available such as jQuery and others. But this can have some performance and incompatibility issues. This can lead to users just going to the next website. The overall look of the website is important too. Where to place certain buttons, where to place certain types of articles such as faq and support. Where and how to display error messages so that the user sees them but are not bothering him. And an overall color scheme is important too. The basic question is: How to create an interface that triggers a user to buy/use your services I know psychology also plays a huge role in how users interact with your website. The color scheme for example is important. When the colors are irritating on a website you just want to click away. I have not found any articles that explain those concept. Does anyone have any tips and/or recourses where i can get some articles that guide you in making the correct choices for your website.

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• Trouble with data not saving with bindings and shared NSUserDefaults in IB

  - by Chief

  I'm having a bit of a strange issue that I can't quite figure out. I'm somewhat of a n00b to Interface Builder. What I am trying to do seems like it should be simple, but it's not working for some reason. In interface builder I have a preferences window with a simple NSTextField. I have set the value binding to the Shared User Defaults Controller with the controller key "values" and model key "test". I build/run my app and open the preferences window, type some random value into said text field, close the window. Command-Q the app. Then in a shell i do a "defaults read com.xxx.yyy" for my app and the key and value are nowhere to be found. That being said, it seems like the next time I fire up the app and change the value it works but only if I switch focus off of the NSTextField before closing the window. In the documentation for NSUserDefaults it says that the shared controller saves values immediately, am I missing something stupid here? Thanks for any help.

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• Custom view with nib as subview doesn't seem to be loading

  - by Ben Collins

  I've created a custom view that loads its content from a nib, like this: /* PricingDataView.h */ #import <UIKit/UIKIt.h> @interface PricingDataView : UIView { UIView *contentView; } @property (nonatomic, retain) IBOutlet UIView *contentView; @end /* PricingDataView.m */ #import "PricingDataView.h" @implementation PricingDataView @synthesize contentView; - (id)initWithFrame:(CGRect)frame { if ((self = [super initWithFrame:frame])) { [[NSBundle mainBundle] loadNibNamed:@"PricingDataView" owner:self options:nil]; [contentView setFrame:frame]; [self addSubview:contentView]; } return self; } /* ... */ In the nib file I set PricingDataView as the type of the File's Owner, and connected the contentView outlet in IB. I placed a regular UIView from the Interface Library onto the full-sized view shown to the user, and then changed it's class name to PricingDataView. It all builds, but at runtime, nothing is rendered where my custom view is supposed to be. I put breakpoints in PricingDataView.initWithFrame, but they don't hit, so I know I'm missing something that would cause the view to be initialized. What I'm curious about is that int the process of loading my other views from nibs, all the initialization happens for me, but not with this one. Why?

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• How to set ExportMetaData with multiple values as well as single w/ custom attribute ?

  - by Matthew M.

  I have the following ExportMetaData attributes set on my class: [Export(typeof(IDocumentViewer))] [ExportMetadata("Name", "MyViewer")] [ExportMetadata("SupportsEditing", true)] [ExportMetadata("Formats", DocFormat.DOC, IsMultiple = true)] [ExportMetadata("Formats", DocFormat.DOCX, IsMultiple = true)] [ExportMetadata("Formats", DocFormat.RTF, IsMultiple = true)] I also have a supporting interface: public interface IDocumentViewerMetaData { /// <summary> /// Gets the format. /// </summary> /// <value>The format.</value> IEnumerable<DocFormat> Formats { get; } /// <summary> /// Gets the name of the viewer /// </summary> /// <value>The name.</value> string Name { get; } /// <summary> /// Gets a value indicating whether this viewer supports editing /// </summary> /// <value><c>true</c> if [supports editing]; otherwise, <c>false</c>.</value> bool SupportsEditing { get; } } And of course my ImportMany: [ImportMany(typeof(IDocumentViewer))] public IEnumerable<Lazy<IDocumentViewer, IDocumentViewerMetaData>> _viewers { get; set; } What I would like to do is use a strongly-typed attribute class instead of using the ExportMetaData attribute. I have not figured out a way to do this while also supporting single values (Name, SupportsEditing, in the example above). I envision doing something similiar the following (or whatever is suggested as best): [Export(typeof(IDocumentViewer))] [DocumentViewerMetadata(Name = "MyViewer")] [DocumentViewerMetadata(SupportsEditing = true)] [DocumentViewerMetadata(Format = DocFormat.DOC)] [DocumentViewerMetadata(Format = DocFormat.DOCX)] I am fairly certain that there IS a way to do this, I just haven't found the right way to connect the dots. :) Thank you, Matthew

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• Can't create new xib files in Xcode projects

  - by Reed Olsen

  This one is a doozy... My buddy just downloaded the iPhone SDK on his Snow Leopard MacBook Pro. No matter what kind of project he creates (Window Based, View Based, etc...,) he can't create or use his own xib files. The project will compile and run fine until he adds a new xib file. Here are some symptoms: When he selects a pre-generated xib in Xcode (such as MainWindow.xib), no preview is shown on the right hand side. Double clicking on this file will open it in interface builder (This is correct behavior). When he selects his own custom xib, the preview pane displays the XML content of the xib. Double clicking on his custom xib opens up the XML file in Xcode - as if it were a standard code file (This is jacked up). Opening his custom xib from finder opens it in Interface Builder. When building the application, the build warning says something to the effect of "Warning: No rule to process file /path/to/CustomXib of type sourcecode.xib for architecture i386" At runtime he gets the error: Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] was unable to load a nib named "MyCustomXib"' We've uninstalled Xcode from the command line and reinstalled. I've verified that it's the right version for his machine. I'm stumped!

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• Subclass of UIView with Xib file.

  - by rdesign

  Hey guys, Although I've searched the Board and used google, I didn't get any useful results. I've trying to make a subclass of UIView loading its view from a xib file. My approach is the following: 1. Creating a subclass (named mySubclass): @interface mySubclass : UIView { } @end Creating a view through: Add New File... User Interface View XIB Connecting the Xib and the subclass: In IB select the View and set the class to mySubclass. In my viewController I make an instance of my new subclass and add to my view. -(void)viewDidLoad { mySubclassIns = [[mySubclass alloc] initWithFrame:CGRectMake(0, 0, 320, 460)]; [self.view addSubview:mySubclassIns]; [super viewDidLoad]; } Result: Noting shows up in my App :( If I don't set it up programmatically but rather with IB it doesn't work either. (Am I setting it up right when choosing a view in IB and set the class to myClass?) I would be really thankful for your help! Thanks in advance.

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• Interfaces with structs, by reference using Generics

  - by Fraga

  I can't pass by reference an interface with a struct in it, what am I doing wrong? Here is the example code: class Processor<T> where T : new() { public Processor() { Data = new T(); } public T Data; } class PeriodsProcessor : Processor<Periods> { public PeriodsProcessor() { DataBase DB = new DataBase(); Console.WriteLine(Data.Value); DB.ModifyData<Period>(Data); Console.WriteLine(Data.Value); Console.ReadLine(); } } public class Period { public string Name; } public interface IDataTable<T> { string Value { get; set; } T Filter { get; set; } } [Serializable] public struct Periods : IDataTable<Period> { public string Value { get; set; } public Period Filter { get; set; } } public class DataBase { public void ModifyData<T>(IDataTable<T> data) where T : new() { data.Value = "CHANGE"; } } class Program { static void Main(string[] args) { PeriodsProcessor PeriodsProcessor = new PeriodsProcessor(); } }

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• Add a new element to a SortedSet

  - by arjacsoh

  Can someone explain me why this code compiles and runs fine, despite the fact that SortedSet is an interface and not a concrete class: public static void main(String[] args) { Integer[] nums = {4, 7, 8, 14, 45, 33}; List<Integer> numList = Arrays.asList(nums); TreeSet<Integer> numSet = new TreeSet<Integer>(); numSet.addAll(numList); SortedSet<Integer> sSet = numSet.subSet(5, 20); sSet.add(17); System.out.println(sSet); } It prints normally the result: [7, 8, 14, 17] Furthermore, my wonder is heightened by the fact that the SortedSet cannot be instansiated (expectedly). This line does not compile: SortedSet<Integer> sSet = new SortedSet<Integer>(); However, if I try the code: public static void main(String[] args) { Integer[] nums = {4, 7, 8, 14, 45, 33}; List<Integer> numList = Arrays.asList(nums); numList.add(56); System.out.println(numList); } it throws an UnsupportedOperationException. I reckon, this comes from the fact that List is an interface and cannot be handled as a concrete class. What is true about SortedSet?

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• Do fluent interfaces significantly impact runtime performance of a .NET application?

  - by stakx

  I'm currently occupying myself with implementing a fluent interface for an existing technology, which would allow code similar to the following snippet: using (var directory = Open.Directory(@"path\to\some\directory")) { using (var file = Open.File("foobar.html").In(directory)) { // ... } } In order to implement such constructs, classes are needed that accumulate arguments and pass them on to other objects. For example, to implement the Open.File(...).In(...) construct, you would need two classes: // handles 'Open.XXX': public static class OpenPhrase { // handles 'Open.File(XXX)': public static OpenFilePhrase File(string filename) { return new OpenFilePhrase(filename); } // handles 'Open.Directory(XXX)': public static DirectoryObject Directory(string path) { // ... } } // handles 'Open.File(XXX).XXX': public class OpenFilePhrase { internal OpenFilePhrase(string filename) { _filename = filename } // handles 'Open.File(XXX).In(XXX): public FileObject In(DirectoryObject directory) { // ... } private readonly string _filename; } That is, the more constituent parts statements such as the initial examples have, the more objects need to be created for passing on arguments to subsequent objects in the chain until the actual statement can finally execute. Question: I am interested in some opinions: Does a fluent interface which is implemented using the above technique significantly impact the runtime performance of an application that uses it? With runtime performance, I refer to both speed and memory usage aspects. Bear in mind that a potentially large number of temporary, argument-saving objects would have to be created for only very brief timespans, which I assume may put a certain pressure on the garbage collector. If you think there is significant performance impact, do you know of a better way to implement fluent interfaces?

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• ArrayAccess multidimensional (un)set?

  - by anomareh

  I have a class implementing ArrayAccess and I'm trying to get it to work with a multidimensional array. exists and get work. set and unset are giving me a problem though. class ArrayTest implements ArrayAccess { private $_arr = array( 'test' => array( 'bar' => 1, 'baz' => 2 ) ); public function offsetExists($name) { return isset($this->_arr[$name]); } public function offsetSet($name, $value) { $this->_arr[$name] = $value; } public function offsetGet($name) { return $this->_arr[$name]; } public function offsetUnset($name) { unset($this->_arr[$name]); } } $arrTest = new ArrayTest(); isset($arrTest['test']['bar']); // Returns TRUE echo $arrTest['test']['baz']; // Echo's 2 unset($arrTest['test']['bar']; // Error $arrTest['test']['bar'] = 5; // Error I know $_arr could just be made public so you could access it directly, but for my implementation it's not desired and is private. The last 2 lines throw an error: Notice: Indirect modification of overloaded element. I know ArrayAccess just generally doesn't work with multidimensional arrays, but is there anyway around this or any somewhat clean implementation that will allow the desired functionality? The best idea I could come up with is using a character as a separator and testing for it in set and unset and acting accordingly. Though this gets really ugly really fast if you're dealing with a variable depth. Does anyone know why exists and get work so as to maybe copy over the functionality? Thanks for any help anyone can offer.

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• Why doesn't IB see my IBAction?

  - by Dan Ray

  I've been staring at this for way too long. There's nothing fancy happening here, and I've done this dozens of times, yet Interface Builder steadfastly refuses to provide me an action target for -(IBAction)slideDirections. I'm at the point where I'm willing to post publicly and feel stupid. So let 'er rip. Here's my .h: #import <UIKit/UIKit.h> #import <MapKit/MapKit.h> @interface PulseDetailController : UIViewController { NSDictionary *pulse; IBOutlet MKMapView *map; IBOutlet UIWebView *directions; IBOutlet UIView *directionsSlider; BOOL directionsExtended; IBOutlet UILabel *vendor; IBOutlet UILabel *offer; IBOutlet UILabel *offerText; IBOutlet UILabel *hours; IBOutlet UILabel *minutes; IBOutlet UILabel *seconds; IBOutlet UILabel *distance } @property (nonatomic, retain) NSDictionary *pulse; @property (nonatomic, retain) MKMapView *map; @property (nonatomic, retain) UIWebView *directions; @property (nonatomic, retain) UIView *directionsSlider; @property (nonatomic) BOOL directionsExtended; @property (nonatomic, retain) UILabel *vendor; @property (nonatomic, retain) UILabel *offer; @property (nonatomic, retain) UILabel *offerText; @property (nonatomic, retain) UILabel *hours; @property (nonatomic, retain) UILabel *minutes; @property (nonatomic, retain) UILabel *seconds; @property (nonatomic, retain) UILabel *distance; -(IBAction)slideDirections; @end

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• Multiple on-screen view controllers in iPhone apps

  - by Felixyz

  I'm creating a lot of custom views and controllers in a lot of my apps and so far I've mostly set them up programmatically, with adjustments and instantiations being controlled from plists. However, now I'm transitioning to using Interface Builder as much as possible (wish I had done that before, was always on my back-list). Apple is recommending against having many view controllers being simultaneously active in iPhone apps, with a couple of well-known exceptions. I've never fully understood why it should be bad to have different parts of the interface belong to different controllers, if they have no interdependent functionality at all. Does having multiple controllers risk messing up the responder chain, or is there some other reason that it's not recommended, except for the fact that it's usually not needed? What I want to be able to do is design reusable views and controls in IB, but since a nib is not associated with a view, but with a view controller, it seems I'd have to have different parts of the screen be connected to different controllers. I know it's possible to have other objects than view controllers being instantiated from nibs. Should I look into how to create my own alternative more light-weight controllers (that could be sub-controllers of a UIViewController) which could be instantiated from nibs?

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• Binding value for NSTableView, but tooltip gets set as well

  - by Mark

  I've set up an NSTableView in Interface Builder to be populated from an NSArray. Each value of the array represents one row in the table. The value is bound correctly, but as a side effect, the table cell's tooltip is set to the string representation of the bound object. In my case, the NSArray contains NSDictiorany objects and the tooltip looks like it could be the [... description] output of that dictionary. Very ugly... I don't want the tooltip to be set at all. I have other tables that have plain NSString values bound to them and they don't have a tooltip set automatically. Is there some Interface Builder magic going on? I tried to start with a blank project - same problem. I should add that the table cell is a custom implementation of NSTextFieldCell that uses an NSButtonCell instance to draw an image and a label into the table. The values are retrieved from the dictionary bound as value. Why is the tooltip set when I only bind the "value" attribute? Thanks in advance!

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• Improve this generic abstract class

  - by Keivan

  I have the following abstract class design, I was wondering if anyone can suggest any improvements in terms of stronger enforcement of our requirements or simplifying implementing of the ControllerBase. //Dependency Provider base public abstract class ControllerBase<TContract, TType> where TType : TContract, class { public static TContract Instance { get { return ComponentFactory.GetComponent<TContract, TType>(); } } public TContract GetComponent<TContract, TType>() where TType : TContract, class { component = (TType)Activator.CreateInstance(typeof(TType), true); RegisterComponentInstance<TContract>(component); } } //Contract public interface IController { void DoThing(); } //Actual Class Logic public class Controller: ControllerBase<IController,Controller> { public void DoThing(); //internal constructor internal Controller(){} } //Usage public static void Main() { Controller.Instance.DoThing(); } The following facts should always be true, TType should always implement TContract (Enforced using a generic constraint) TContract must be an interface (Can't find a way to enforce it) TType shouldn't have public constructor, just an internal one, is there any way to Enforce that using ControllerBase? TType must be an concrete class (Didn't include New() as a generic constrain since the constructors should be marked as Internal)

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• How to call implemented method of generic enum in Java?

  - by Justin Wiseman

  I am trying pass an enum into a method, iterate over that enums values, and call the method that that enum implements on all of those values. I am getting compiler errors on the part "value.getAlias()". It says "The method getAlias() is undefined for the type E" I have attempted to indicate that E implements the HasAlias interface, but it does not seem to work. Is this possible, and if so, how do I fix the code below to do what I want? The code below is only meant to show my process, it is not my intention to just print the names of the values in an enum, but to demonstate my problem. public interface HasAlias{ String getAlias(); }; public enum Letters implements HasAlias { A("The letter A"), B("The letter B"); private final String alias; public String getAlias(){return alias;} public Letters(String alias) { this.alias = alias; } } public enum Numbers implements HasAlias { ONE("The number one"), TWO("The number two"); private final String alias; public String getAlias(){return alias;} public Letters(String alias) { this.alias = alias; } } public class Identifier { public <E extends Enum<? extends HasAlias>> void identify(Class<E> enumClass) { for(E value : enumClass.getEnumConstants()) { System.out.println(value.getAlias()); } } }

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