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• Why are UUID / GUID's in the format they are?

  - by Xeoncross

  Globally Unique Identifiers (GUID) are a grouped string with a specific format which I assume has a security reason. A GUID is most commonly written in text as a sequence of hexadecimal digits separated into five groups, such as: 3F2504E0-4F89-11D3-9A0C-0305E82C3301 Why aren't GUID/UUID strings just random bytes encoded using hexadecimal of X length? This text notation contains the following fields, separated by hyphens: | Hex digits | Description |------------------------- | 8 | Data1 | 4 | Data2 | 4 | Data3 | 4 | Initial two bytes from Data4 | 12 | Remaining six bytes from Data4 There are also several versions of the UUID standards. Version 4 UUIDs are generally internally stored as a raw array of 128 bits, and typically displayed in a format something like: uuid:xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

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• MATLAB: draw centroids

  - by Myx

  Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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• Java - converting String in array to double

  - by cc0

  I'm stuck with this pretty silly thing; I got a textfile like this; Hello::140.0::Bye I split it into a string array using; LS = line.split("::"); Then I try to convert the array values containing the number to a double, like this; Double number = Double.parseDouble(LS[1]); But I get the following error message; Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1 Does anyone have any idea why this doesn't work?

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• How do we know the correct moves of Tower of Hanoi?

  - by Saqib

  We know that: In case of iterative solution: Alternating between the smallest and the next-smallest disks, follow the steps for the appropriate case: For an even number of disks: make the legal move between pegs A and B make the legal move between pegs A and C make the legal move between pegs B and C repeat until complete For an odd number of disks: make the legal move between pegs A and C make the legal move between pegs A and B make the legal move between pegs B and C repeat until complete In case of recursive solution: To move n discs from peg A to peg C: move n-1 discs from A to B. This leaves disc n alone on peg A move disc n from A to C move n-1 discs from B to C so they sit on disc n Now the questions are: How did we get this two solutions? Only by intuition? Or by logical/mathematical computation? If computation, how?

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• How can I find the nearest intersection via the Google Maps API?

  - by dusoft

  How can I find the closest intersection of the street I have coordinates of? For instance, say I have street A running from south to north that is crossed by street X on the north and by street Y on the south. Does the Google Maps API allow for finding coordinates of the nearest crossroad (either X or Y) of street A? I couldn't find it mentioned anywhere. PS: The only solution I am aware of is to guess the lowest number and the highest number of building on the street A and to draw polyline between them. I am not sure about this though.

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• controlling bluetooth connection in matlab

  - by Mehreen Shahid

  we have a project in which we have to pick randomly generated numbers from a remote device, say mobile. there is a simple java application to generate numbers. next, we have to recieve those numbers in our matlab program via bluetooth connection with the device. assuming those numbers are temperature readings, we want to recieve a new number after every 10 sec and display the number on our matlab GUI program. the problem is do we implement bluetooth protocol through our programming? or use the matlab templates? because otherwise whenever we want to transfer file from a mobile to computer, we have to manually click "recieve a file" in blutooth wizard , just like we normally do to transfer a file. we want to enable the connection once, and then recieve text files after every 10 seconds to be read in our matlab program. can anyone please tell is it even possible in matlab? if yes, how do we establish such an automatic real time connection?

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• Sorting a list of variable length integers delimited by decimal points...

  - by brewerdc

  Hey guys, I'm in need of some help. I have a list of delimited integer values that I need to sort. An example: Typical (alpha?) sort: 1.1.32.22 11.2.4 2.1.3.4 2.11.23.1.2 2.3.7 3.12.3.5 Correct (numerical) sort: 1.1.32.22 2.1.3.4 2.3.7 2.11.23.1.2 3.12.3.5 11.2.4 I'm having trouble figuring out how to setup the algorithm to do such a sort with n number of decimal delimiters and m number of integer fields. Any ideas? This has to have been done before. Let me know if you need more information. Thanks a bunch! -Daniel

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• How to compare filename of uploaded file and string

  - by user225269

  I use this code to upload image files in xammp server: <?php if ((($_FILES["file"]["type"] == "image/gif") || ($_FILES["file"]["type"] == "image/jpeg") || ($_FILES["file"]["type"] == "image/pjpeg")) && ($_FILES["file"]["size"] < 100000)) { if ($_FILES["file"]["error"] > 0) { echo "Return Code: " . $_FILES["file"]["error"] . "<br />"; } else { echo "Upload: " . $_FILES["file"]["name"] . "<br />"; echo "Type: " . $_FILES["file"]["type"] . "<br />"; echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />"; echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />"; if (file_exists("upload/" . $_FILES["file"]["name"])) { echo $_FILES["file"]["name"] . " already exists. "; } else { move_uploaded_file($_FILES["file"]["tmp_name"], "upload/" . $_FILES["file"]["name"]); echo "Stored in: " . "upload/" . $_FILES["file"]["name"]; } } } else { echo "Invalid file, File must be less than 100Kb in size with .jpg, .jpeg, or .gif file extension"; } ?> What do I do to compare the file name of the uploaded files with the text inputted by the user? My goal is to be able to compare the user input(ID number) and the file name of the image file which should also be an ID number. So that I will be able to display the image that corresponds with the ID Number provided. What do I need to do?Please give me an idea on how can I achieve this. Thanks

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• In Python, how to use a C++ function which returns an allocated array of structs via a ** parameter?

  - by Jon-Eric

  I'd like to use some existing C++ code, NvTriStrip, in a Python tool. SWIG easily handles the functions with simple parameters, but the main function, GenerateStrips, is much more complicated. What do I need to put in the SWIG interface file to indicate that primGroups is really an output parameter and that it must be cleaned up with delete[]? /////////////////////////////////////////////////////////////////////////// // GenerateStrips() // // in_indices: input index list, the indices you would use to render // in_numIndices: number of entries in in_indices // primGroups: array of optimized/stripified PrimitiveGroups // numGroups: number of groups returned // // Be sure to call delete[] on the returned primGroups to avoid leaking mem // bool GenerateStrips( const unsigned short* in_indices, const unsigned int in_numIndices, PrimitiveGroup** primGroups, unsigned short* numGroups, bool validateEnabled = false ); FYI, here is the PrimitiveGroup declaration: enum PrimType { PT_LIST, PT_STRIP, PT_FAN }; struct PrimitiveGroup { PrimType type; unsigned int numIndices; unsigned short* indices; PrimitiveGroup() : type(PT_STRIP), numIndices(0), indices(NULL) {} ~PrimitiveGroup() { if(indices) delete[] indices; indices = NULL; } };

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• Check if row already exists, if so tell the referenced table the id

  - by flhe

  Let's assume I have a table magazine: CREATE TABLE magazine ( magazine_id integer NOT NULL DEFAULT nextval(('public.magazine_magazine_id_seq'::text)::regclass), longname character varying(1000), shortname character varying(200), issn character varying(9), CONSTRAINT pk_magazine PRIMARY KEY (magazine_id) ); And another table issue: CREATE TABLE issue ( issue_id integer NOT NULL DEFAULT nextval(('public.issue_issue_id_seq'::text)::regclass), number integer, year integer, volume integer, fk_magazine_id integer, CONSTRAINT pk_issue PRIMARY KEY (issue_id), CONSTRAINT fk_magazine_id FOREIGN KEY (fk_magazine_id) REFERENCES magazine (magazine_id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION ); Current INSERTS: INSERT INTO magazine (longname,shotname,issn) VALUES ('a long name','ee','1111-2222'); INSERT INTO issue (fk_magazine_id,number,year,volume) VALUES (currval('magazine_magazine_id_seq'),'8','1982','6'); Now a row should only be inserted into 'magazine', if it does not already exist. However if it exists, the table 'issue' needs to get the 'magazine_id' of the row that already exists in order to establish the reference. How can i do this? Thx in advance!

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• What is the best way to launch a website to make it go viral?

  - by Talvi Watia

  Say for example I have a website that has finished BETA and is ready for full launch. I'm at the stage now I want it to be very visible to start getting traffic. Right now, I am just getting some random search engine hits, word of mouth and a few referrals. How do I break out of this and really get some serious traffic to my site? Do I need to launch a huge ad-campaign? If so, what is the best/most cost effective way to do this? I have tried google adwords but at $0.45+ a click this jsut isn't practical for what I have.

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• Do we need Record Level Locking when we already have Transaction for online ordering? (of concert ti

  - by Jian Lin

  For online ordering of concert seat or airline ticket, do we need Record Level Locking or is Transaction good enough? For concert ticket (say, seat Number 20B), or airline ticket (even with overbooking, the limit is 210, for example), I think the website cannot lock any record or begin transaction when showing the ticket purchase screen. But after the user clicks "Confirm Purchase", then the server should Begin a Transaction, Purchase Seat Number 20B, and try to Commit. If another user already bought Seat 20B in a previous transaction, then it is the "Commit" part that the current transaction will fail? So... we don't need Record Level Locking? Do Transactions always go serialized (one after another), so that's why we can know for sure there is no "race condition"? In what situation is Record Level Locking needed then?

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• How to define a natural id in database?

  - by gcc

  There are a lot of manuals. I am trying to create an database to hold information of these documents. But, there is a small problem. How can I give meaningful id to the manuals? Are there any standard or logic behind the giving meaningful id to the documents? If there is no standard, can you tell me how I should do that? example: table : manual id | manual name EDIT: Not Meaningful ID 1 or M1 or foo 2 C2 bar 3 P123 name ... ... ... (i) (ii) (iii) (i) Not meaningful for me because if some item deleted, there can be gap. ex 1 33 100. (ii) random character can be confusing when one try to give a name to new manual (iii) Why giving name is not preferred is because finding a name to the manual as ID is hard after 500 manuals. Meaningful : New ID * Can be easily produced even if after 1000 manuals * Should not be so complicated

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• How would you create a string of all UTF-8 characters? [PHP]

  - by Xeoncross

  There are many ways to represent the +1 million UTF-8 characters. Take the latin capital "A" with macron (A). This is unicode code point U+0100, hex number 0xc4 0x80, decimal number 196 128, and binary 11000100 10000000. I would like to create a collection of the first 65,535 UTF-8 characters for use in testing applications. These are all unicode characters up to code point U+FFFF (byte3). Is it possible to do something like a for($x=0) loop and then convert the resulting decimal to another base (like hex) which would allow the creation of the matching unicode character? I can create the value A using something like this: $char = "\xc4\x80"; // or $char = chr(196).chr(128); However, I am not sure how to turn this into an automated process. // fail! $char = "\x". dechex($a). "\x". dexhex($$b);

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• How to create list of numbers and append its reverse to it efficiently in Ruby

  - by Kiwi

  Given a minimum integer and maximum integer, I want to create an array which counts from the minimum to the maximum by two, then back down (again by two, repeating the maximum number). For example, if the minimum number is 1 and the maximum is 9, I want [1, 3, 5, 7, 9, 9, 7, 5, 3, 1]. I'm trying to be as concise as possible, which is why I'm using one-liners. In Python, I would do this: range(1, 10, 2) + range(9, 0, -2) In Ruby, which I'm just beginning to learn, all I've come up with so far is: (1..9).inject([]) { |r, num| num%2 == 1 ? r << num : r }.reverse.inject([]) { |r, num| r.unshift(num).push(num) } Which works, but I know there must be a better way. What is it?

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• Basic Conditional Checking for IF statements in C

  - by ZaZu

  Hi there, Can someone please explain what really goes on in this code ? If I put the AND statement, the message wont show if values are less than 0 or greater than 10 ... I think I must use 1 0 logic to work this out right ? I just need someone to briefly explain it please. #include<stdio.h> main(){ puts("enter number"); scanf("%d",num); if(num<0 || num >10) puts("yay"); } How is that IF statement different when AND is put : #include<stdio.h> main(){ puts("enter number"); scanf("%d",num); if(num<0 && num >10) puts("yay"); } Thanks !!

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• How can I write cocoa bindings as code instead of in the Interface Builder?

  - by johnjohndoe

  In my modell got an NSMutableArray that keeps track of a changing number of elements. In my view I got a NSTextField that shows the number of elements. The view gots unarchived from the nib file and alloc/inits the modell. Therefore it knowns about the modell and the contained array. I established the connection as follows. In the Interface Builder at the textfield I added a Cocoa Binding "path" like this: myModell.myArray.@count. By this I can access the count property (which is a must since the array itself does not change). The binding is based on key-value compliance which I established at the modell so the array can be accessed. But key-value compliance is not part of the questions. My question: How can I put the binding into the sourcecode and not writing it into the Interface Builder?

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• Abstract skill/talent system implementation

  - by kiliki

  I've been making small 2D games for about 3 years now (XNA and more recently LWJGL/Slick2D). My latest idea would involve some form of "talent tree" system in a real time game. I've been wracking my brain but can't think of a structure to hold a talent. Something like "Your melee attack is an instant kill if behind the target" I'd like to come up with an abstract object rather than putting random conditionals into other methods. I've solved some relatively complex problems before but I don't even know where to begin with this one. Any help would be appreciated - Java, pseudocode or general concepts are all great.

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• Array basics - Populating with loop

  - by madlan

  Hi, I'm looping through a zip file trying to add the file name of each file within. Is this the correct method? Dim ZipNameArray(?) Using zip As ZipFile = ZipFile.Read(ZipToUnpack) For Each file In zip ZipNameArray(?) = file .FileName Next End Using I do not know the array size until I start looping through the zip (To work out the number of files within). How do I increment the Array? file is not a number? (It's a ZipEntry)

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• What are the disadvantages of naming things alphabetically?

  - by JoJo

  Let me give you an example of how I name my classes alphabetically: Car CarHonda (subclass of Car) CarHondaAccord (subclass of CarHonda) There are two reasons why I put the type of the class earlier in its name: When browsing your files alphabetically in a file explorer, related items appear grouped together and parent classes appear above child classes. I can progressively refine auto-complete in my IDE. First I type the major type, then the secondary type, and so on without having to memorize what exactly I named the last part of the thing. My question is why do I hardly see any other programmers do this? They usually name things in reverse or some random order. Take the iOS SDK for example: UIViewController UITableViewController What are the disadvantages of my naming convention and the advantages of their convention?

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• binary search question

  - by Phenom

  For binary search, what is the average number of comparisons needed to find a record in a file?

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• Circle physics and collision using vectors

  - by Joe Hearty

  This is a problem I've been having, When making a set number of filled circles at random locations on a JPanel and applying a gravity (a negative change in the y), each of the circles collide. I want them to have collision detection and push in the opposite direction using vectors but I don't know how to apply that to my scenario could someone help? public void drawballs(Graphics g){ g.setColor (Color.white); //displays circles for(int i = 0; i<xlocationofcircles.length-1; i++){ g.fillOval( (int) xlocationofcircles[i], (int) (ylocationofcircles[i]) ,16 ,16 ); ylocationofcircles[i]+=.2; //gravity if(ylocationofcircles[i] > 550) //stops gravity at bottom of screen ylocationofcircles[i]-=.2; //Check distance between circles(i think..) float distance =(xlocationofcircles[i+1]-xlocationofcircles[i]) + (ylocationofcircles[i+1]-xlocationofcircles[i]); if( Math.sqrt(distance) <16) ...

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• Proper password handling for login

  - by piers

  I have read a lot about PHP login security recently, but many questions on Stack Overflow regarding security are outdated. I understand bcrypt is one of the best ways of hashing passwords today. However, for my site, I believe sha512 will do very well, at least to begin with. (I mean bcrypt is for bigger sites, sites that require high security, right?) I´m also wonder about salting. Is it necessary for every password to have its own unique salt? Should I have one field for the salt and one for the password in my database table? What would be a decent salt today? Should I join the username together with the password and add a random word/letter/special character combination to it? Thanks for your help!

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• TechEd 2012: MVVM In XAML

  - by Tim Murphy

  Paul Sheriff was a real character at the start of his MVVM in XAML session.  There was a lot of sarcasm and self deprecation going on prior to the .  That is never a bad way to get things rolling right after lunch.  Then things got semi-serious. The presentation itself had a number of surprises, but not all of them had to do with XAML.  When he flipped over his company’s code generation tool it took me off guard.  I am used to generator that create code for a whole project, but his tools were able to create different types of constructs on demand.  It also made it easier to follow what he was doing than some of the other demos I have seen this week where people were using code snippets. Getting to the heart of the topic I found myself thinking that I may have found my utopia for application development in MVVM.  Yes, I know there is no such thing, but this comes closer than any other pattern I have learned about.  This pattern allows the application to have better separation of concerns than I have seen before.  This is especially true since you can leverage data binding.  I’m not sure why it has taken me so long to find time for this subject. As Paul demonstrated using this pattern with XAML gives you multi-platform reusable code when you leverage common utility classes and ModelView classes.  The one drawback I see is that you have to go to the lowest common denominator between the platforms you want to support, but you always have to weigh the trade offs. And finally, the Visual Studio nuggets just keep coming.  Even though it has been available for several generations of Visual Studio I have never seen someone use linked files within a solution.  It just goes to show that I should spend more time exploring the deeper features of each dialog. del.icio.us Tags: TechEd,TechEd 2012,MVVM,Paul Sheriff,Patterns,Visual Studio 2012

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• Why does Facebook convert PHP code to C++?

  - by user72245

  I read that Facebook started out in PHP, and then to gain speed, they now compile PHP as C++ code. If that's the case why don't they: Just program in c++? Surely there must be SOME errors/bugs when hitting a magic compiler button that ports PHP to c++ code , right? If this impressive converter works so nicely, why stick to PHP at all? Why not use something like Ruby or Python? Note -- I picked these two at random, but mostly because nearly everyone says coding in those languages is a "joy". So why not develop in a super great language and then hit the magic c++ compile button?

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