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• What are the common compliance standards for software products?

  - by Jay

  This is a very generic question about software products. I would like to know what compliance standards are applicable to any software product. I know that question gives away nothing. So, here is an example to what I am referring to. CiSecurity Security Certification/Compliance lists out products ceritified by them to be compliant to the standards published at their website, i.e, cisecurity.org. Compliance could be as simple as answering a questionnaire for your product and approved by a thirdparty like cisecurity or it could apply to your whole organization, for instance, PCI-DSS compliance. I would be very interested in knowing the standards that products you know/designed/created, comply to. To give you the context behind this question: I am the developer of a data-masking tool. The said tool helps mask onscreen html text in a banking web application using filters. So, for instance, if the bank application lists out user information with ssn, my product when integrated with the banking product, automatically identifies ssn pattern and masks it into a pre-defined format.So, I have my product marketing team wanting more buzz words like compliance to be able to sell it to more banking clients. Hence, understanding "compliances that apply to products" is a key research item for me at this point. By which I meant, security compliances. Appreciate all your help and suggestions.

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• How is a functional programming-based javascript app laid out?

  - by user321521

  I've been working with node.js for awhile on a chat app (I know, very original, but I figured it'd be a good learning project). Underscore.js provides a lot of functional programming concepts which look interesting, so I'd like to understand how a functional program in javascript would be setup. From my understanding of functional programming (which may be wrong), the whole idea is to avoid side effects, which are basically having a function which updates another variable outside of the function so something like var external; function foo() { external = 'bar'; } foo(); would be creating a side effect, correct? So as a general rule, you want to avoid disturbing variables in the global scope. Ok, so how does that work when you're dealing with objects and what not? For example, a lot of times, I'll have a constructor and an init method that initializes the object, like so: var Foo = function(initVars) { this.init(initVars); } Foo.prototype.init = function(initVars) { this.bar1 = initVars['bar1']; this.bar2 = initVars['bar2']; //.... } var myFoo = new Foo({'bar1': '1', 'bar2': '2'}); So my init method is intentionally causing side effects, but what would be a functional way to handle the same sort of situation? Also, if anyone could point me to either a python or javascript source code of a program that tries to be as functional as possible, that would also be much appreciated. I feel like I'm close to "getting it", but I'm just not quite there. Mainly I'm interested in how functional programming works with traditional OOP classes concept (or does away with it for something different if that's the case).

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• Java inheritance and super() isn't working as expected

  - by dwwilson66

  For a homework assignment, I'm working with the following. It's an assigned class structure, I know it's not the best design by a long shot. Class | Extends | Variables -------------------------------------------------------- Person | None | firstName, lastName, streetAddress, zipCode, phone CollegeEmployee | Person | ssn, salary,deptName Faculty | CollegeEmployee | tenure(boolean) Student | person | GPA,major So in the Faculty class... public class Faculty extends CollegeEmployee { protected String booleanFlag; protected boolean tenured; public Faculty(String firstName, String lastName, String streetAddress, String zipCode, String phoneNumber,String ssn, String department,double salary) { super(firstName,lastName,streetAddress,zipCode,phoneNumber, ssn,department,salary); String booleanFlag = JOptionPane.showInputDialog (null, "Tenured (Y/N)?"); if(booleanFlag.equals("Y")) tenured = true; else tenured = false; } } It was my understanding that super() in Faculty would allow access to the variables in CollegeEmployee as well as Person. With the code above, it compiles fine when I ONLY include the Person variables. As soon as I try to use ssn, department, or salary I get the following compile errors. Faculty.java:15: error: constructor CollegeEmployee in class CollegeEmployee can not be applied to the given types: super(firstName,lastName,streetAddress,zipCode,phoneNumber,ssn,department,salary); ^ Required: String,String,String,String,String Found: String,String,String,String,String,String,String,String reason: actual and formal argument lists differ in length I'm completely confused by this error...which is the actual and formal? Person has five arguments, CollegeEmployee has 3, so my guess is that something's funky with how the parameters are being passed...but I'm not quite sure where to begin fixing it. What am I missing?

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• how to update UI controls in cocoa application from background thread

  - by AmitSri

  following is .m code: #import "ThreadLabAppDelegate.h" @interface ThreadLabAppDelegate() - (void)processStart; - (void)processCompleted; @end @implementation ThreadLabAppDelegate @synthesize isProcessStarted; - (void)awakeFromNib { //Set levelindicator's maximum value [levelIndicator setMaxValue:1000]; } - (void)dealloc { //Never called while debugging ???? [super dealloc]; } - (IBAction)startProcess:(id)sender { //Set process flag to true self.isProcessStarted=YES; //Start Animation [spinIndicator startAnimation:nil]; //perform selector in background thread [self performSelectorInBackground:@selector(processStart) withObject:nil]; } - (IBAction)stopProcess:(id)sender { //Stop Animation [spinIndicator stopAnimation:nil]; //set process flag to false self.isProcessStarted=NO; } - (void)processStart { int counter = 0; while (counter != 1000) { NSLog(@"Counter : %d",counter); //Sleep background thread to reduce CPU usage [NSThread sleepForTimeInterval:0.01]; //set the level indicator value to showing progress [levelIndicator setIntValue:counter]; //increment counter counter++; } //Notify main thread for process completed [self performSelectorOnMainThread:@selector(processCompleted) withObject:nil waitUntilDone:NO]; } - (void)processCompleted { //Stop Animation [spinIndicator stopAnimation:nil]; //set process flag to false self.isProcessStarted=NO; } @end I need to clear following things as per the above code. How to interrupt/cancel processStart while loop from UI control? I also need to show the counter value in main UI, which i suppose to do with performSelectorOnMainThread and passing argument. Just want to know, is there anyother way to do that? When my app started it is showing 1 thread in Activity Monitor, but when i started the processStart() in background thread its creating two new thread,which makes the total 3 thread until or unless loop get finished.After completing the loop i can see 2 threads. So, my understanding is that, 2 thread created when i called performSelectorInBackground, but what about the thrid thread, from where it got created? What if thread counts get increases on every call of selector.How to control that or my implementation is bad for such kind of requirements? Thanks

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• postgresql help with php loop....

  - by KnockKnockWhosThere

  I keep getting an "Notice: Undefined index: did" error with this query, and I'm not understanding why... I'm much more used to mysql, so, maybe the syntax is wrong? This is the php query code: function get_demos() { global $session; $demo = array(); $result = pg_query("SELECT DISTINCT(did,vid,iid,value) FROM dv"); if(pg_num_rows($result) > 0) { while($r = pg_fetch_array($result)) { switch($r['did']) { case 1: $demo['a'][$r['vid']] = $r['value']; break; case 2: $demo['b'][$r['vid']] = $r['value']; break; case 3: $demo['c'][$r['vid']] = $r['value']; break; } } } else { $session->session_setMessage(2); } return $demo; } When I run that query at the pg prompt, I get results: "(1,1,1,"A")" "(1,2,2,"B")" "(1,3,3,"C")" "(1,4,4,"D")" "(1,5,5,"E")" "(1,6,6,"F")" "(1,7,7,"G")" "(1,8,8,"H")" "(1,9,9,"I")" "(1,10,A,"J")" "(1,11,B,"K")" "(1,12,C,"L")" "(1,13,D,"M")" "(2,14,1,"A")" "(2,15,2,"B")" "(2,16,0,"C")" "(3,17,1,"A")" "(3,18,2,"B")" "(3,19,3,"C")" "(3,20,4,"D")" "(3,21,5,"E")" "(3,22,6,"F")" "(3,23,7,"G")"

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• How do I use price data in one table for a calculation that is stored in another table?

  - by shane

  I'm still leanring PHP/MySQL but have learned quite a bit thanks to codies on StackOverflow. I'm trying to setup a sort of room reservations system using two tables: SETUP: Room price table: Has, prices for a type room a client may want to rent as well as the dates (day of week) they wish to use it. Pricing varies based on day of the week and per room. I've setup a different table for each room type as each room type carries different pricing for each day of the week. So, There is an Alpha room table, Bravo room, etc. Within Alpha table are headers for the days of the week with pricing pre-entered into the rows. Client info table: Has the name, address, date of room use, etc data for the specific client. EXAMPLE: Alpha-room price table: Sun = $100; Mon = $200; Tue=$300 and so on. Bravo-room price table: Sun = $100; Mon = $200; Tue=$300 and so on. Client data table: ClientName; date-of-room-use; address; day_subtotal; grand_total. QUESTION: I'm trying to find PHP code that will: look at the date of room use in the client data table, look up the associated cost for that date in the specific room pricing table, record that unit cost in the day subtotal of the client data table and sum a grand total in the grand total row of the client data table (assuming the room may be used more than one day by the customer). I know there's something to do with join but I'm finding it difficult to grasp the concept and, if someone can demonstrate using this example, I think I will have a better understanding of how to work this sort of transaction. Thank you ALL in advance for your suggestions or alternatvie approaches.

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• Pointers, am I doing them correctly? Objective-c/cocoa

  - by Chris

  I have this in my @interface struct track currentTrack; struct track previousTrack; int anInt; Since these are not objects, I do not have to have them like int* anInt right? And if setting non-object values like ints, boolean, etc, I do not have to release the old value right (assuming non-GC environment)? The struct contains objects: typedef struct track { NSString* theId; NSString* title; } *track; Am I doing that correctly? Lastly, I access the struct like this: [currentTrack.title ...]; currentTrack.theId = @"asdf"; //LINE 1 I'm also manually managing the memory (from a setter) for the struct like this: [currentTrack.title autorelease]; currentTrack.title = [newTitle retain]; If I'm understanding the garbage collection correctly, I should be able to ditch that and just set it like LINE 1 (above)? Also with garbage collection, I don't need a dealloc method right? If I use garbage collection does this mean it only runs on OS 10.5+? And any other thing I should know before I switch to garbage collected code? Sorry there are so many questions. Very new to objective-c and desktop programming. Thanks

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• Am I making the right choice in choosing Yii as my PHP Framework?

  - by Bara

  I am about to begin development of a new website and have been doing research on PHP Frameworks. I'm not an advanced PHP developer, but I have been developing web sites and apps (in asp.net) for a few years now. My website will primarily be AJAX-based (using jQuery) and making lots of calls to web services. After some research, here's what I came up with: CakePHP: Originally started developing in this, but found it too complex. The fact that it forces you to use and learn all this new stuff just to use it was a bit daunting, so I put it aside for the time being. Zend: The performance of the framework leaves me a bit skeptical, but I heard it has great support for creating web services. I also heard it was a bit complex. CodeIgniter: No real reason for not using this one. Based on what I've read CodeIgniter and Yii are very similar, but Yii is a bit faster and doesn't have un-needed code for PHP4 (since I plan on developing exclusively in PHP5). As far as Yii, the only things that scare me about it are that it is newer than the other frameworks so it has a smaller community. It also doesn't seem to have a ton of web service support (only SOAP, from my understanding) as opposed to Zend. So my questions come down to: Should these things worry me? (not as big of a community, poor web service support) Is there anything else I should look into? Is my choice of Yii over the other frameworks ok for a primarily AJAX-based web app? Bara

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• Question about how to implement a c# host application with a plugin-like architecture

  - by devoured elysium

  I want to have an application that works as a Host to many other small applications. Each one of those applications should work as kind of plugin to this main application. I call them plugins not in the sense they add something to the main application, but because they can only work with this Host application as they depend on some of its services. My idea was to have each of those plugins run in a different app domain. The problem seems to be that my host application should have a set of services that my plugins will want to use and from what is my understanding making data flow in and out from different app domains is not that great of a thing. On one hand I'd like them to behave as stand-alone applications(although, as I said, they need to use lots of times the host application services), but on the other hand I'd like that if any of them crashes, my main application wouldn't suffer from it. What is the best (.NET) approach to this kind of situation? Make them all run on the same AppDomain but each one in a different Thread? Use different AppDomains? One for each "plugin"? How would I make them communicate with the Host Application? Any other way of doing this? Although speed is not an issue here, I wouldn't like for function calls to be that much slower than they are when we're working with just a regular .NET application. Thanks

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• Transaction to find an entity - locks all entities of that type?

  - by user246114

  Hi, Reading the docs for transactions: http://code.google.com/appengine/docs/java/datastore/transactions.html An example provided shows one way to make an instance of an object: try { tx.begin(); Key k = KeyFactory.createKey("SalesAccount", id); try { account = pm.getObjectById(Employee.class, k); } catch (JDOObjectNotFoundException e) { account = new SalesAccount(); account.setId(id); } ... When the above transaction gets executed, it will probably block all other write attempts on Account objects? I'm wondering because I'd like to have a user signup which checks for a username or email already in use: tx.begin(); "select from User where mUsername == str1 LIMIT 1"; if (count > 0) { throw new Exception("username already in use!"); } "select from User where mEmail == str1 LIMIT 1"; if (count > 0) { throw new Exception("email already in use!"); } pm.makePersistent(user(username, email)); // ok. tx.commit(); but the above would be even more time consuming I think, making an even worse bottleneck? Am I understanding what will happen correctly? Thanks

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• SQLDeveloper using over 100MB of PGA+UGA

  - by Leigh Riffel

  Perhaps this is normal, but in my Oracle 11g database I am seeing programmers using Oracle's SQL Developer regularly consume more than 100MB of combined UGA and PGA memory. I'd like to know if this is normal and what can be done about it. Our database is on the 32 bit version of Windows 2008, so memory limitations are becoming an increasing concern. I am using the following query to show the memory usage: SELECT e.SID, e.username, e.status, b.PGA_MEMORY FROM v$session e LEFT JOIN (select y.SID, y.value pga, TO_CHAR(ROUND(y.value/1024/1024),99999999) || ' MB' PGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC# and NAME = 'session pga memory') b ON e.sid=b.sid WHERE (PGA)/1024/1024 > 20 ORDER BY 4 DESC; It seems that the resource usage goes up any time a table is opened in SQLDeveloper, but even when it is closed the memory does not go away. The problem is worse if the table is sorted while it was open as that seems to use even more memory. I understand how this would use memory while it is sorting, and perhaps even while it is still open, but to use memory after it is closed seems wrong to me. Can anyone confirm this? Update: I discovered that my numbers were off due to not understanding that the UGA is stored in the PGA under dedicated server mode. This makes the numbers lower than they were, but the problem still remains that SQL Developer seems to use excessive PGA.

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• Applying fine-grained security to an existing application

  - by Mark

  I've inherited a reasonably large and complex ASP.NET MVC3 web application using EF Code First on SQL Server. It uses ASP.NET Membership roles with database authentication. The controller actions are secured with attributes derived from AuthorizeAttribute that map roles to actions. There are extension methods for the finer points, such as showing a particular widget to particular roles. This is works great and I have a good understanding of the current security model. I've been asked to provide finer grained security at the data level. For example a 'Customer' user can only see data (throughout the database) associated with themselves and not other Customers. The problem is that 'Customer' is only 1 of 5 different types with their own specific restrictions (each of the 9 roles is one of these 5 types). The best thing I can think of is to go through all the data repositories and extend each and every LINQ statements/query with a filter for every user type. Even if I had time for that it doesn't seem like the most elegant way. Any suggestions? I really don't know where to start with this so anything could be helpful. Many thanks.

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• can javascript process binary data?

  - by Johnny

  admit me describe my questions in situation-oriented way: assume IE is still the dominate web browser(the firefox have document for binary processing): the XMLHttpRequest.responseText or XMLHttpRequest.responseXML in ie desire txt or xml/xhtml/html,but what about the server response the xmlHttprequest whith MIME TYPE application/octet ? would the response string all little than 256 ?(every char of that string < 256), thanks very much for a straight answer, i have no webserver env,so i don't know how to test it out. because use txt or xml have a issue of character set encode, and i don't know how to process #[[[CDDATA node of one encoded xml(ex : utf-8,ascii,gb18030) with javascript, when i getNodeText, does the docObj return me byte or decoded char ? if it was decoded char which according to the header indicated charSet in the httpresponse , it would be all wrong. to avoid mess up with charSet ,i would like the server to response octet data and force strings data to be encoded as utf-8 but another charSet in the binary format. if the response is octal, so i guess the browser would not try to decode the response"txt" does this weird? or miss understanding the fundamental things? EDIT: I believe the question is asking this: Can Javascript safely process strings that aren't encoded in Unicode? What are the problems with trying to do so? EDIT: no no no , i means if http-header: content-type is "application/octet" , would the ie try to decoded it as (16bits Unicode | ie local setting charset ) when i get XMLHttpRequestobj.responseText use javascript ? or it(ie) just wrap every single byte of the response body as a javascript string, then every char in that string little than or equal 256 (char<=256), am i talking Mars language? sadly, if i were Marsizen,i would come as tourist without fuzzy questions. however i am in a country which share at least one property with Mars : RED

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• Generic InBetween Function.

  - by Luiscencio

  I am tired of writing x > min && x < max so i wawnt to write a simple function but I am not sure if I am doing it right... actually I am not cuz I get an error: bool inBetween<T>(T x, T min, T max) where T:IComparable { return (x > min && x < max); } errors: Operator '>' cannot be applied to operands of type 'T' and 'T' Operator '<' cannot be applied to operands of type 'T' and 'T' may I have a bad understanding of the where part in the function declaring note: for those who are going to tell me that I will be writing more code than before... think on readability =) any help will be appreciated EDIT deleted cuz it was resolved =) ANOTHER EDIT so after some headache I came out with this (ummm) thing following @Jay Idea of extreme readability: public static class test { public static comparision Between<T>(this T a,T b) where T : IComparable { var ttt = new comparision(); ttt.init(a); ttt.result = a.CompareTo(b) > 0; return ttt; } public static bool And<T>(this comparision state, T c) where T : IComparable { return state.a.CompareTo(c) < 0 && state.result; } public class comparision { public IComparable a; public bool result; public void init<T>(T ia) where T : IComparable { a = ia; } } } now you can compare anything with extreme readability =) what do you think.. I am no performance guru so any tweaks are welcome

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• Why is JavaMail Transport.send() a static method?

  - by skiphoppy

  I'm revising code I did not write that uses JavaMail, and having a little trouble understanding why the JavaMail API is designed the way it is. I have the feeling that if I understood, I could be doing a better job. We call: transport = session.getTransport("smtp"); transport.connect(hostName, port, user, password); So why is Eclipse warning me that this: transport.send(message, message.getAllRecipients()); is a call to a static method? Why am I getting a Transport object and providing settings that are specific to it if I can't use that object to send the message? How does the Transport class even know what server and other settings to use to send the message? It's working fine, which is hard to believe. What if I had instantiated Transport objects for two different servers; how would it know which one to use? In the course of writing this question, I've discovered that I should really be calling: transport.sendMessage(message, message.getAllRecipients()); So what is the purpose of the static Transport.send() method? Is this just poor design, or is there a reason it is this way?

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• Why my object sees variables which were not given to it in the constructor?

  - by Roman

  I have the following code. Which is "correct" and which I do not understand: private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } I create a new instance of the Runnable class and then in the run method of this instance I use variables label and i. It works, but I do not understand why it work. Why the considered object sees values of these variables. According to my understanding the code should look like that (and its wrong): private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } So, I would give the i and label variables to the constructor so the object can access them... By the way, in the updateGUI I use final before the i and label. I think I used final because compiler wanted that. But I do not understand why.

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• ResourceFilterFactory and non-Path annotated Resources

  - by tousdan

  (I'm using Jersey 1.7) I am attempting to add a ResourceFilterFactory in my project to select which filters are used per method using annotations. The ResourceFilterFactory seems to be able to filters on Resources which are annotated with the Path annotation but it would seem that it does not attempt to generate filters for the methods of the SubResourceLocator of the resources that are called. @Path("a") public class A { //sub resource locator? @Path("b") public B getB() { return new B(); } @GET public void doGet() {} } public class B { @GET public void doOtherGet() { } @Path("c") public void doInner() { } } When ran, the Filter factory will only be called for the following: AbstractResourceMethod(A#doGet) AbstractSubResourceLocator(A#getB) When I expected it to be called for every method of the sub resource. I'm currently using the following options in my web.xml; <init-param> <param-name>com.sun.jersey.spi.container.ResourceFilters</param-name> <param-value>com.my.MyResourceFilterFactory</param-value> </init-param> <init-param> <param-name>com.sun.jersey.config.property.packages</param-name> <param-value>com.my.resources</param-value> </init-param> Is my understanding of the filter factory flawed?

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• how to return a list using SwingWorker

  - by Ender

  I have an assignment where i have to create an Image Gallery which uses a SwingWorker to load the images froma a file, once the image is load you can flip threw the image and have a slideshow play. I am having trouble getting the list of loaded images using SwingWorker. This is what happens in the background it just publishes the results to a TextArea // In a thread @Override public List<Image> doInBackground() { List<Image> images = new ArrayList<Image>(); for (File filename : filenames) { try { //File file = new File(filename); System.out.println("Attempting to add: " + filename.getAbsolutePath()); images.add(ImageIO.read(filename)); publish("Loaded " + filename); System.out.println("Added file" + filename.getAbsolutePath()); } catch (IOException ioe) { publish("Error loading " + filename); } } return images; } } when it is done I just insert the images in a List<Image> and that is all it does. // In the EDT @Override protected void done() { try { for (Image image : get()) { list.add(image); } } catch (Exception e) { } } Also I created an method that returns the list called getImages() what I need to get is the list from getImages() but doesn't seam to work when I call execute() for example MySwingWorkerClass swingworker = new MySwingWorkerClass(log,list,filenames); swingworker.execute(); imageList = swingworker.getImage() Once it reaches the imageList it doesn't return anything the only way I was able to get the list was when i used the run() instead of the execute() is there another way to get the list or is the run() method the only way?. or perhaps i am not understanding the Swing Worker Class.

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• NSTimer as a timeout mechanism

  - by alexantd

  I'm pretty sure this is really simple, and I'm just missing something obvious. I have an app that needs to download data from a web service for display in a UITableView, and I want to display a UIAlertView if the operation takes more than X seconds to complete. So this is what I've got (simplified for brevity): MyViewController.h @interface MyViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> { NSTimer *timer; } @property (nonatomic, retain) NSTimer *timer; MyViewController.m @implementation MyViewController @synthesize timer; - (void)viewDidLoad { timer = [NSTimer scheduledTimerWithTimeInterval:20 target:self selector:@selector(initializationTimedOut:) userInfo:nil repeats:NO]; [self doSomethingThatTakesALongTime]; [timer invalidate]; } - (void)doSomethingThatTakesALongTime { sleep(30); // for testing only // web service calls etc. go here } - (void)initializationTimedOut:(NSTimer *)theTimer { // show the alert view } My problem is that I'm expecting the [self doSomethingThatTakesALongTime] call to block while the timer keeps counting, and I'm thinking that if it finishes before the timer is done counting down, it will return control of the thread to viewDidLoad where [timer invalidate] will proceed to cancel the timer. Obviously my understanding of how timers/threads work is flawed here because the way the code is written, the timer never goes off. However, if I remove the [timer invalidate], it does.

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• Fluent NHibernate Repository with subclasses

  - by reallyJim

  Having some difficulty understanding the best way to implement subclasses with a generic repository using Fluent NHibernate. I have a base class and two subclasses, say: public abstract class Person { public virtual int PersonId { get; set; } public virtual string FirstName { get; set; } public virtual string LastName { get; set; } } public class Student : Person { public virtual decimal GPA { get; set; } } public class Teacher : Person { public virtual decimal Salary { get; set; } } My Mappings are as follows: public class PersonMap : ClassMap { public PersonMap() { Table("Persons"); Id(x => x.PersonId).GeneratedBy.Identity(); Map(x => x.FirstName); Map(x => x.LastName); } } public class StudentMap : SubclassMap<Student> { public StudentMap() { Table("Students"); KeyColumn("PersonId"); Map(x => x.GPA); } } public class TeacherMap : SubclassMap<Teacher> { public TeacherMap() { Table("Teachers"); KeyColumn("PersonId"); Map(x => x.Salary); } } I use a generic repository to save/retreive/update the entities, and it works great--provided I'm working with Repository--where I already know that I'm working with students or working with teachers. The problem I run into is this: What happens when I have an ID, and need to determine the TYPE of person? If a user comes to my site as PersonId = 23, how do I go about figuring out which type of person it is?

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• Beginner Question: For extract a large subset of a table from MySQL, how does Indexing, order of tab

  - by chongman

  Sorry if this is too simple, but thanks in advance for helping. This is for MySQL but might be relevant for other RDMBSs tblA has 4 columns: colA, colB, colC, mydata, A_id It has about 10^9 records, with 10^3 distinct values for colA, colB, colC. tblB has 3 columns: colA, colB, B_id It has about 10^4 records. I want all the records from tblA (except the A_id) that have a match in tblB. In other words, I want to use tblB to describe the subset that I want to extract and then extract those records from tblA. Namely: SELECT a.colA, a.colB, a.colC, a.mydata FROM tblA as a INNER JOIN tblB as b ON a.colA=b.colA a.colB=b.colB ; It's taking a really long time (more than an hour) on a newish computer (4GB, Core2Quad, ubuntu), and I just want to check my understanding of the following optimization steps. ** Suppose this is the only query I will ever run on these tables. So ignore the need to run other queries. Now my questions: 1) What indexes should I create to optimize this query? I think I just need a multiple index on (colA, colB) for both tables. I don't think I need separate indexes for colA and colB. Another stack overflow article (that I can't find) mentioned that when adding new indexes, it is slower when there are existing indexes, so that might be a reason to use the multiple index. 2) Is INNER JOIN correct? I just want results where a match is found. 3) Is it faster if I join (tblA to tblB) or the other way around, (tblB to tblA)? This previous answer says that the optimizer should take care of that. 4) Does the order of the part after ON matter? This previous answer say that the optimizer also takes care of the execution order.

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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• setBit java method using bit shifting and hexadecimal code - question

  - by somewhat_confused

  I am having trouble understanding what is happening in the two lines with the 0xFF7F and the one below it. There is a link here that explains it to some degree. http://www.herongyang.com/java/Bit-String-Set-Bit-to-Byte-Array.html I don't know if 0xFF7FposBit) & oldByte) & 0x00FF are supposed to be 3 values 'AND'ed together or how this is supposed to be read. If anyone can clarify what is happening here a little better, I would greatly appreciate it. private static void setBit(byte[] data, final int pos, final int val) { int posByte = pos/8; int posBit = pos%8; byte oldByte = data[posByte]; oldByte = (byte) (((0xFF7F>>posBit) & oldByte) & 0x00FF); byte newByte = (byte) ((val<<(8-(posBit+1))) | oldByte); data[posByte] = newByte; } passed into this method as parameters from a selectBits method was setBit(out,i,val); out = is byte[] out = new byte[numOfBytes]; (numOfBytes can be 7 in this situation) i = which is number [57], the original number from the PC1 int array holding the 56-integers. val = which is the bit taken from the byte array from the getBit() method.

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• Linux C debugging library to detect memory corruptions

  - by calandoa

  When working sometimes ago on an embedded system with a simple MMU, I used to program dynamically this MMU to detect memory corruptions. For instance, at some moment at runtime, the foo variable was overwritten with some unexpected data (probably by a dangling pointer or whatever). So I added the additional debugging code : at init, the memory used by foo was indicated as a forbidden region to the MMU; each time foo was accessed on purpose, access to the region was allowed just before then forbidden just after; a MMU irq handler was added to dump the master and the address responsible of the violation. This was actually some kind of watchpoint, but directly self-handled by the code itself. Now, I would like to reuse the same trick, but on a x86 platform. The problem is that I am very far from understanding how is working the MMU on this platform, and how it is used by Linux, but I wonder if any library/tool/system call already exist to deal with this problem. Note that I am aware that various tools exist like Valgrind or GDB to manage memory problems, but as far as I know, none of these tools car be dynamically reconfigured by the debugged code. I am mainly interested for user space under Linux, but any info on kernel mode or under Windows is also welcome!

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• How do you verify that 2 copies of a VB 6 executable came from the same code base?

  - by Tim Visher

  I have a program under version control that has gone through multiple releases. A situation came up today where someone had somehow managed to point to an old copy of the program and thus was encountering bugs that have since been fixed. I'd like to go back and just delete all the old copies of the program (keeping them around is a company policy that dates from before version control was common and should no longer be necessary) but I need a way of verifying that I can generate the exact same executable that is better than saying "The old one came out of this commit so this one should be the same." My initial thought was to simply MD5 hash the executable, store the hash file in source control, and be done with it but I've come up against a problem which I can't even parse. It seems that every time the executable is generated (method: Open Project. File Make X.exe) it hashes differently. I've noticed that Visual Basic messes with files every time the project is opened in seemingly random ways but I didn't think that would make it into the executable, nor do I have any evidence that that is indeed what's happening. To try to guard against that I tried generating the executable multiple times within the same IDE session and checking the hashes but they continued to be different every time. So that's: Generate Executable Generate MD5 Checksum: md5sum X.exe > X.md5 Verify MD5 for current executable: md5sum -c X.md5 Generate New Executable Verify MD5 for new executable: md5sum -c X.md5 Fail verification because computed checksum doesn't match. I'm not understanding something about either MD5 or the way VB 6 is generating the executable but I'm also not married to the idea of using MD5. If there is a better way to verify that two executables are indeed the same then I'm all ears. Thanks in advance for your help!

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