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• perf events documentation

  - by Thanatos

  I've searched for an exhaustive explanation of the meaning of each event monitored by the perf stat command; I've found a tutorial which explains quite well how to use different the features of the perf tool. However, it doesn't explain the meaning of several events that can be observed (and there are a lot!!). Someone know where is a quite simple and complete documentation about the events listed by the perf list command? In particular, I'm interested in finding out the percentage of cpu used by some application I wrote. Can i measure it directly through cpu-clock or task-clock? What's the meaning of these two events? Thanks in advance

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• How do you create a daemon in Python?

  - by DavidM

  Searching on Google reveals x2 code snippets. The first result is to this code recipe which has a lot of documentation and explanation, along with some useful discussion underneath. However, another code sample, whilst not containing so much documentation, includes sample code for passing commands such as start, stop and restart. It also creates a PID file which can be handy for checking if the daemon is already running etc. These samples both explain how to create the daemon. Are there any additional things that need to be considered? Is one sample better than the other, and why?

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• Strange type in c++

  - by Cemre

  I have a method with the prototype: bool getAssignment(const Query& query, Assignment *&result); I am a bit confused about the type of the second param (Assignment *&result) since I don't think I have seen something like that before. It is used like: Assignment *a; if (!getAssignment(query, a)) return false; Is it a reference to a pointer or the other way around ? or neither ? Any explanation is appreciated. Thanks.

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• how to create english language dictionary application with python (django)?

  - by sintaloo

  Hi All, I would like to create an online dictionary application by using python (or with django). It will be similar to http://dictionary.reference.com/. My question is (1) Are there any existing open source python package or modules or application which implements this functionality that I can use or study from? (2) If the answer to the first question is NO. which algorithm should I follow to create such web application? Can I simply use the python built-in dictionary object for this job? so that the dictionary object's key will be the english word and the value will be the explanation. is this OK in term of performance? OR Do I have to create my own Tree Object to speed up the search? or any existing package which handles this job properly? Thank you very much.

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• Removing Item From List - during iteration - what's wrong with this idiom ?

  - by monojohnny

  As an experiment, I did this: letters=['a','b','c','d','e','f','g','h','i','j','k','l'] for i in letters: letters.remove(i) print letters The last print shows that not all items were removed ? (every other was). IDLE 2.6.2 >>> ================================ RESTART ================================ >>> ['b', 'd', 'f', 'h', 'j', 'l'] >>> What's the explanation for this ? How it could this be re-written to remove every item ?

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• Reading a bmp file and inverting it in C

  - by user1763396

  I have an assignment that deals with reading a bmp file into memory, inverts the pixels, and then saves the inverted image to a new file. From this description it seems fairly easy, however I don't think my professor did a great job in explaining the necessary steps to go about doing so. He taught us about fread and fwrite but there is so much more. Can anyone explain the process in going about this problem (I'm no looking for a direct answer just an explanation). Here is the link to the problem's description: https://engineering.purdue.edu/OOSD/F2012/Exercises/ex5.html Thanks in advance for any sort of help. NOTE: I actually have looked into this problem but since I don't have a good standing on this info it's not quite "clicking".

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• jsp and java beans

  - by JRR

  I am building jsp pages hosted on tomcat and am wondering if the bean instances referenced in each jsp are stateless / stateful? How do those bean instances come about? Are they (re-)created each time when the page is visited? Do I need to worry about two different users visiting the same page at the same time and getting hold of the same bean instance? In general I find the interaction between jsp and beans quite confusing so I'd appreciate if someone can refer a tutorial / explanation of those concepts. Thanks!

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• Prevent keypress whilst shift key is held

  - by deifwud

  I'm trying to prevent certain keys from being entered into an input box, but only if that particular key is pressed whilst the shift key is held: $('selector').keydown(function(e) { console.log(e.shiftKey); if (e.shiftKey && e.which == 51) { e.preventDefault(); alert('Disallowed'); } }); The alert fires but the character still appears in the text box. If I remove e.shiftKey from the if statement and press the key (without shift held), the alert fires and the character does not appear in the text box. I've tried searching around for an explanation as to why this happens but to no avail, any help would be greatly appreciated! edit Removing the alert seems to fix the problem (which seems bizarre), I'd really love to know why it behaves in this way though, it doesn't seem to make any sense. Thanks

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• Multiple selection in a TreeView

  - by Frederick

  I am using a Windows Forms TreeView control in my program. I would like to allow the user to select multiple nodes at the same level by dragging their mouse pointer around (also called a "lasso" selection). I don't think a standard TreeView allows that. My question is what would be the best way to achieve this? Do I have to write custom selection behaviour of my own in perhaps a custom or derived control? Where do I start? I don't need a detailed explanation. Just a small nudge in the right direction.

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• In Android, does _id have to be present in any table created?

  - by Andy

  I am trying to create a table to only has a foreign key, not a primary key. I am getting this error: java.lang.IllegalArgumentException: column '_id' does not exist I read a tutorial that the primary key must be _id, with no explanation. And that is fine. But what if I do not want a primary key! What if I only want a foreign key. I am assuming this is where my problem lies. The schemas below are what I have. But the third one is where I assume this is coming from. database.execSQL("CREATE TABLE events (" + "_id INTEGER PRIMARY KEY, event_name TEXT" + ")"); database.execSQL("CREATE TABLE reminders(_id INTEGER PRIMARY KEY, event_name TEXT" + ")"); database.execSQL("CREATE TABLE events_info (_id INTEGER, event_name TEXT, all_day INTEGER, " + "start_date INTEGER, start_time INTEGER, end_date INTEGER, end_time INTEGER," + " location TEXT, reminder_id INTEGER, notes TEXT, repeat TEXT," + "FOREIGN KEY(_id) REFERENCES events(_id), FOREIGN KEY(reminder_id) REFERENCES reminders(_id))" );

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• Need help in understanding a SELECT query

  - by Grant Smith

  I have a following query. It uses only one table (Customers) from Northwind database. I completely have no idea how does it work, and what its intention is. I hope there is a lot of DBAs here so I ask for explanation. particularly don't know what the OVER and PARTITION does here. WITH NumberedWomen AS ( SELECT CustomerId ,ROW_NUMBER() OVER ( PARTITION BY c.Country ORDER BY LEN(c.CompanyName) ASC ) women FROM Customers c ) SELECT * FROM NumberedWomen WHERE women > 3 If you needed the db schema, it is here

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• How to suppress a MongoDDException when proxy can't find a referenced document

  - by Madarco

  We are using Symfony2/DoctrineOdm/MongoDB and when we do: if ($doc.referenceOne != null) { ... } and the $doc.referenceOne contains a MongoDbRef that point to a deleted/lost document, the Doctrine Proxy object raises a MongoDBException. It is possible to tell the Proxy return null instead of raising the exception? Detailed Explanation: Our document: class User { /* @MongoDB\ReferenceOne( ... ) */ private $photo; } If $photo contains a MongoDbRef, but the document is lost/deleted, when we do if ($user.photo) { ... } doctrine will raise a MongoDBException: The "Proxies\DocumentPhotoProxy" document with identifier "4fd8b3ef732bafab7b000000" could not be found We want to suppress the exception since our application can handle null values in that variable. (we could simply log that error, while the exception propagate to a 500 page and disrupt our service)

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• Host unavailable when user is logged off

  - by aksamit

  I am facing a problem that I discovered while I was implementing a small client/host application. The client side runs Windows 7 64-bit and machine never turns off but user is automatically logged off after 30 minutes of inactivity. When user is automatically logged off the host becomes unreachable, first I thought the problem was isolated to my application, but after som investigation I discoverd that resources and vnc server is also unavailable. The question might be a bit off limit for this forum but I can't find any reasonable explanation somewhere else. Does anyone know how I can keep user being logged off automatically but with the host still reachable on the network?

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• C++ dynamic array sizing problem

  - by Peter

  The basic pseudo code looks like this: void myFunction() { int size = 10; int * MyArray; MyArray = new int[size]; cout << size << endl; cout << sizeof(MyArray) << endl; } The first cout returns 10, as expected, while the second cout returns 4. Anyone have an explanation?

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• What is the trick in pAddress & ~(PAGE_SIZE - 1) to get the page's base address

  - by Dbger

  Following function is used to get the page's base address of an address which is inside this page: void* GetPageAddress(void* pAddress) { return (void*)((ULONG_PTR)pAddress & ~(PAGE_SIZE - 1)); } But I couldn't quite get it, what is the trick it plays here? Conclusion: Personally, I think Amardeep's explanation plus Alex B's example are best answers. As Alex B's answer has already been voted up, I would like to accept Amardeep's answer as the official one to highlight it! Thanks you all.

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• What is the differance between those two Strings in Java

  - by user1816808

  why when we declare string in java we can't use == to compare this string and always will turn to false while if we initialize the string from the beginning it will be true . for example : import java.util.Scanner; public class MyString { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub Scanner input = new Scanner(System.in); String s = input.nextLine(); if(s=="Hello") system.out.println("Hello"); String d = "Hello"; if(d=="Hello") system.out.println("Hello"); } } I need an explanation please ??

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• android question about service and the method onstartcommand

  - by user516883

  In a service class there is a method to start the service. If that service gets done executing does it runs onstartcommand from the beginning? Is onstartcommand sorta like a loop as long as the service is running. For example i have onstartcommand { int x = 0; if(x == 0){ } else{ } } After that is complete does it run it again. If you know that answer please explain. I have read google explanation of services and it did not explain that part very well. Is onstartcommand sorta like a loop as long as the service is runnning

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• Background subtracting in MATLAB

  - by eiphyomin

  I'm looking to do background subtracting on an image. I'm new to MATLAB and new to image processing/analysis, so sorry if any of this sounds stupid. 1) Other than imsubtract() are there other ways to do background subtracting (besides comparing one image to another)? 2) In the Math Works explanation for imsubtract() why do they make their structuring element a disk? This seems rather difficult so far because every time I try something, I end up not only subtracting the noisy background but also losing the parts of the image I want to look at!

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• password limitations in SQL Server and MySql

  - by asteroid

  Does MySql 5.1 and SQL Server 2008 (Web edition, Standard) have any functional password limitations other than length limits? Are metacharacters in any form a bad idea to use, like bang, pipe, hash, any slash, carrot, and so on? I know that MySql 5.1 has a password length limitation of 16 characters that is hardcoded, but I was wondering, are any metacharacters (i.e. non alphanumerics) a bad idea to use? And is this true in SQL Server 2008 Web edition, Standard? So specifically: can symbols like: /`~:}{[]^ be used successfully? I would hope it doesn't matter to the database, but I don't understand enough about password storage in enterprise database systems yet to know for sure, and I was looking for confirmation or an explanation.

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• What is the main purpose of WebExceptionStatus.Success?

  - by csharpenter

  I am a bit confused about the purpose of the enum value Success of the WebExceptionStatus enumeration. I did a search and did not find this enumeration being used outside the WebException class. This is very confusing to me. Why would an exception be used to indicate a successful action/state. Am I missing something, or did I not search thouroughly enough? Was it introduced for future functionality? Please if anyone does know its basic purpose I would be thankfull if s/he shares with us the explanation.

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• Find consecutive sub-vectors of length k out of a numeric vector which satisfy a given condition

  - by user3559153

  I have a numeric vector in R, say v= c(2,3,5,6,7,6,3,2,3,4,5,7,8,9,6,1,1,2,5,6,7,11,2,3,4). Now, I have to find all the consecutive sub-vector of size 4 out of it with the condition that each element of the sub-vector must be greater than 2 and all sub-vector must be disjoint in the sense that non of the two sub-vector can contain same index element. So my output will be: (3,5,6,7),(3,4,5,7),(5,6,7,11). [Explanation: c(2,3,5,6,7,6,3,2,3,4,5,7,8,9,6,1,3,2,5,6,7,11,2,3,4) ]

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• Unexpected output on initializing array by using both `element-by-element` & `designated` technique

  - by haccks

  C99 provides a feature to initialize arrays by using both element-by-element & designated method together as: int a[] = {2,1,[3] = 5,[5] = 9,6,[8] = 4}; On running the code: #include <stdio.h> int main() { int a[] = {2,1,[3] = 5,[0] = 9,4,[6] = 25}; for(int i = 0; i < sizeof(a)/sizeof(a[0]); i++) printf("%d ",a[i]); return 0; } (Note that Element 0 is initialized to 2 and then again initialised by designator [0] to 9) I was expecting that element 0(which is 2) will be replaced by 9(as designator [0] = 9) and hence o/p will become 9 1 0 5 4 0 25 Unfortunately I was wrong as o/p came; 9 4 0 5 0 0 25 Any explanation for unexpected o/p?

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• Android streamming video from camera

  - by user1415651

  Sorry about my English i hope that can be understandable... I'm working on one App for Android and my purpose is to stream video over the phone camera to other Android phone (application). I don´t know so much about streamming video, and what i want to know is what i need to do.. I need to create a streamming server that receive the video from one android phone? How i do this? And what is the best way to do this? how i can set up/configure a streamming server? someone can help me with some explanation or tutorials? Thanks in advance!

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• Javascript, jQuery - how signed actions to just created object?

  - by sebap123

  I am trying to make simple list with ability to add and delete elements. For now I am working on adding and performing a simple action on each of list elements object (existing and added). Unfortunately I have met some difficulties with that. I am able to modify objects that are created at the beginning, but not one added during "webpage working". First of all my idea was to add AJAX to this, but I don't think it is the easiest way. I think that some time ago (I don't remember where) I read how to make this work, but now I don't know. I would be really glad if someone would help me with this or at least give a link to good explanation of this. There is what I have done so far (well this is mostly just a scratch, but the main idea is in it): http://jsfiddle.net/sebap123/pAZ7H/ Thank you for all responses.

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• Why does this Bash regex match return an Exit Status of "2"?

  - by PreservedMoose

  I'm writing a Bash script that needs to scan for the existence of non-ASCII characters in filenames. I'm using the POSIX bracket regex syntax to match the non-ASCII characters, but for some reason, when I test for the match in an if/then statement, the test always returns an Exit Status of 2, and never matches my test string. Here's the code in question: FILEREQ_SOURCEFILE="Filename–WithNonAScII-Charàcters-05sec_23.98.mov" REGEX_MATCH_NONASCII="[^[:ascii:]]" if [[ $FILEREQ_SOURCEFILE =~ $REGEX_MATCH_NONASCII ]]; then echo "Exit Status: $?" echo "Matched!" else echo "Exit Status: $?" echo "No Match" fi This code always returns: Exit Status: 2 No Match I've read and re-read the bash-hackers.org explanation of how regex matching works, as well as this previous question on SO regarding matching non-ASCII characters, but for the life of me, I can't get this to work. What am I missing here?

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