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  • How do I create and read non-global variables that aren't destroyed at end of function?

    - by Paul Reilly
    I am attempting to code some plugins to use with MIDI sequencers but have hit a stumbling block. I can't use global-scope variables to store information because multiple instances of the .dll can exist which share memory. How do I create a class (for re-usability purposes in other plugins) containing 2 dimensional array and other variables the content of which is to be shared between functions? If that is possible, how would I read and write the data from the function in the framework where I do the processing?

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  • How important is it to unset variables in PHP?

    - by dd0x
    I am somewhat new to PHP and I am wondering: How important is it to unset variables in PHP? I know in languages like C we free the allocated memory to prevent leaks, etc. By using unset on variables when I am done with them, will this significantly increase performance of my applications? Also is there a benchmark anywhere that compares difference between using unset and not using unset?

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  • What are common uses of condition variables in C++?

    - by jasonline
    I'm trying to learn about condition variables. I would like to know what are the common situations where condition variables are used. One example is in a blocking queue, where two threads access the queue - the producer thread pushes an item into the queue, while the consumer thread pops an item from the queue. If the queue is empty, the consumer thread is waiting until a signal is sent by the producer thread. What are other design situations where you need a condition variable to be used?

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  • Is a string formatter that pulls variables from its calling scope bad practice?

    - by Eric
    I have some code that does an awful lot of string formatting, Often, I end up with code along the lines of: "...".format(x=x, y=y, z=z, foo=foo, ...) Where I'm trying to interpolate a large number of variables into a large string. Is there a good reason not to write a function like this that uses the inspect module to find variables to interpolate? import inspect def interpolate(s): return s.format(**inspect.currentframe().f_back.f_locals) def generateTheString(x): y = foo(x) z = x + y # more calculations go here return interpolate("{x}, {y}, {z}")

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  • Should I map a domain object to a view model using an optional constructor?

    - by Byron Sommardahl
    I'd like to be able to map a domain model to a view model by newing up a view model and passing in the contributing domain model as a parameter (like the code below). My motivation is to keep from re-using mapping code AND to provide a simple way to map (not using automapper yet). A friend says the view model should not know anything about the "payment" domain model that's being passed into the optional constructor. What do you think? public class LineItemsViewModel { public LineItemsViewModel() { } public LineItemsViewModel(IPayment payment) { LineItemColumnHeaders = payment.MerchantContext.Profile.UiPreferences.LineItemColumnHeaders; LineItems = LineItemDomainToViewModelMapper.MapToViewModel(payment.LineItems); ConvenienceFeeAmount = payment.ConvenienceFee.Fee; SubTotal = payment.PaymentAmount; Total = payment.PaymentAmount + payment.ConvenienceFee.Fee; } public IEnumerable<Dictionary<int, string>> LineItems { get; set; } public Dictionary<int, string> LineItemColumnHeaders { get; set; } public decimal SubTotal { get; set; } public decimal ConvenienceFeeAmount { get; set; } public decimal Total { get; set; } }

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  • Temporary Tables in Stored Procedures

    - by Paul White
    Ask anyone what the primary advantage of temporary tables over table variables is, and the chances are they will say that temporary tables support statistics and table variables do not. This is true, of course; even the indexes that enforce PRIMARY KEY and UNIQUE constraints on table variables do not have populated statistics associated with them, and it is not possible to manually create statistics or non-constraint indexes on table variables. Intuitively, then, any query that has alternative execution...(read more)

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  • How can I share variables between a base class and subclass in Perl?

    - by Jonathan
    I have a base class like this: package MyClass; use vars qw/$ME list of vars/; use Exporter; @ISA = qw/Exporter/; @EXPORT_OK = qw/ many variables & functions/; %EXPORT_TAGS = (all => \@EXPORT_OK ); sub my_method { } sub other_methods etc { } --- more code--- I want to subclass MyClass, but only for one method. package MySubclass; use MyClass; use vars qw/@ISA/; @ISA = 'MyClass'; sub my_method { --- new method } And I want to call this MySubclass like I would the original MyClass, and still have access to all of the variables and functions from Exporter. However I am having problems getting the Exporter variables from the original class, MyClass, to export correctly. Do I need to run Exporter again inside the subclass? That seems redundant and unclear. Example file: #!/usr/bin/perl use MySubclass /$ME/; -- rest of code But I get compile errors when I try to import the $ME variable. Any suggestions?

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  • What are the drawbacks of using PHP to create variables in my CSS stylesheet?

    - by Greg
    One significant drawback of CSS is that one can't use variables. For example, I'd like to use variables to control the location of imported CSS, and it would be awesome to create variables for colors that are used repeatedly in a design. One approach is to use a PHP file for the CSS stylesheet. In other words, create a "style.php" with... <?php header("Content-type: text/css"); ?> ...at the top of the file, and then link to it using... <link href="style.php" rel="stylesheet" type="text/css" /> ...in any file that uses these styles. So what's the catch? I think it might be performance -- I did a few quick experiments in Firefox/Firebug and as one would expect, the CSS stylesheet is cached, but the PHP stylesheet isn't. So we're paying the price of an additional GET. The other annoying thing is that TextMate does not syntax highlight properly for CSS in a .php file. Are there other drawbacks? Have you used this approach, and if so, would you recommend it?

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  • Wait on multiple condition variables on Linux without unnecessary sleeps?

    - by Joseph Garvin
    I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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  • What does it mean to say "Instance variables are not over-rided" in java?

    - by Ankit
    I am aware of the concept called field hiding in java. But still I am having a confusion in relation to instance variable being not over-ridden. According to my present knowledge, overriding a method of super-class means that the JVM will call the sub-class's over-ridden method though the super-class's method is available to the sub-class. And I read the similar thing for field hiding via the link:- Hiding Fields So, in any case we are over-ridding the instance if we change the values of the inherited instance variable in the sub-class. I am confused please help. I am using the following super-class:- public class Animal{ File picture; String food; int hunger; int width, height; int xcoord, ycoord; public void makeNoise(){ ......... } public void eat(){ ............. } public void sleep(){ .......... } public void roam(){ ............. } } It has sub-classes like Tiger, cat, dog,hippo etc. The sub-classes over-ride the makeNoise(), eat and roam() method. But each sub-class also uses a different set of values for instance variables. So as per my confusion, I am kind-of overriding all the instance variables and 3 methods of the super-class Animal; and I still have the super-class instance variables available to the sub-class with the use of the super keyword.

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  • is using private shared objects/variables on class level harmful ?

    - by haansi
    Hello, Thanks for your attention and time. I need your opinion on an basic architectural issue please. In page behind classes I am using a private and shared object and variables (list or just client or simplay int id) to temporary hold data coming from database or class library. This object is used temporarily to catch data and than to return, pass to some function or binding a control. 1st: Can this approach harm any way ? I couldn't analyze it but a thought was using such shared variables may replace data in it when multiple users may be sending request at a time? 2nd: Please comment also on using such variables in BLL (to hold data coming from DAL/database). In this example every time new object of BLL class will be made. Here is sample code: public class ClientManager { Client objclient = new Client(); //Used in 1st and 2nd method List<Client> clientlist = new List<Client>();// used in 3rd and 4th method ClientRepository objclientRep = new ClientRepository(); public List<Client> GetClients() { return clientlist = objclientRep.GetClients(); } public List<Client> SearchClients(string Keyword) { return clientlist = objclientRep.SearchClients(Keyword); } public Client GetaClient(int ClientId) { return objclient = objclientRep.GetaClient(ClientId); } public Client GetClientDetailForConfirmOrder(int UserId) { return objclientRep.GetClientDetailForConfirmOrder(UserId); } } I am really thankful to you for sparing time and paying kind attention.

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  • Java - How to declare table[i][j] elements as instance variables?

    - by JDelage
    All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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  • How can I create global context variables in JBOSS?

    - by NobodyMan
    This is a follow-up to a question I posted a while back: "Can I use a single WAR in multiple environments?". I was able to create a single-war solution in Tomcat, but now we are migrating our app to JBoss 4.2 and I can't figure out how to set up global environment variables. In Tomcat 6 this was pretty straightforward: I simply put the following snippet in tomcat/conf/Catalina/myappname.xml: <Context ...> <Environment name="TARGET_ENV" value="DEV" type="java.lang.String" override="false"/> </Context> Then in my app I was able to resolve the environment name with the following: Context context = (Context) InitialContext().lookup("java:comp/env"); String targetEnvironment = (String) context.lookup("TARGET_ENV"); The problem is that I can't find out where/how to place global variables in JBoss. I've tried putting the <Environment> tag in the following files to no avail: server/all/deploy/jboss-web.deployer/context.xml server/default/deploy/jboss-web.deployer/context.xml I know that I can put environment variables in my app's web.xml but that defeats the purpose of having a unified war - I'd still need custom .war's for dev, qa and prod. I'm a JBoss newbie so if there's any additional information that would help just let me know and I'll append to this question. Many thanks! --N

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  • When should we use private variables and when should we use properties.

    - by Shantanu Gupta
    In most of the cases we usually creates a private variable and its corresponding public properties and uses them for performing our functionalities. Everyone has different approach like some ppl uses properties every where and some uses private variables within a same class as they are private and opens it to be used by external environment by using properties. Suppose I takes a scenario say insertion in a database. I creates some parameters that need to be initialized. I creates 10 private variables and their corresp public properties which are given as private string name; public string Name { get{return name;} set{name=value;} } and so on. In these cases what should be used internally variables or properties. And in those cases like public string Name { get{return name;} set{name=value>5?5:0;} //or any action can be done. this is just an eg. } In such cases what should be done.

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  • When should we use private variables and when should we use properties. Do Backing Fields should be

    - by Shantanu Gupta
    In most of the cases we usually creates a private variable and its corresponding public properties and uses them for performing our functionalities. Everyone has different approach like some people uses properties every where and some uses private variables within a same class as they are private and opens it to be used by external environment by using properties. Suppose I takes a scenario say insertion in a database. I creates some parameters that need to be initialized. I creates 10 private variables and their corresp public properties which are given as private string name; public string Name { get{return name;} set{name=value;} } and so on. In these cases mentioned above, what should be used internal variables or properties. And in those cases like public string Name { get{return name;} set{name=value>5?5:0;} //or any action can be done. this is just an eg. } In such cases what should be done.

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  • Why aren't variables declared in "try" in scope in "catch" or "finally"?

    - by Jon Schneider
    In C# and in Java (and possibly other languages as well), variables declared in a "try" block are not in scope in the corresponding "catch" or "finally" blocks. For example, the following code does not compile: try { String s = "test"; // (more code...) } catch { Console.Out.WriteLine(s); //Java fans: think "System.out.println" here instead } In this code, a compile-time error occurs on the reference to s in the catch block, because s is only in scope in the try block. (In Java, the compile error is "s cannot be resolved"; in C#, it's "The name 's' does not exist in the current context".) The general solution to this issue seems to be to instead declare variables just before the try block, instead of within the try block: String s; try { s = "test"; // (more code...) } catch { Console.Out.WriteLine(s); //Java fans: think "System.out.println" here instead } However, at least to me, (1) this feels like a clunky solution, and (2) it results in the variables having a larger scope than the programmer intended (the entire remainder of the method, instead of only in the context of the try-catch-finally). My question is, what were/are the rationale(s) behind this language design decision (in Java, in C#, and/or in any other applicable languages)?

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  • How can i add a checkbox for optional files during install? (innosetup)

    - by Globulorozzo
    i'm trying to make a custom checkbox in my custom page (because is a one page installer), is needed only a checkbox without dialogs or anything, the installer that i'm trying to compile is very linear and simple. i want to bind "FILE3.EXE" on a checkbox in this way: if checkbox is checked copy the file (FILE3.EXE) in DestDir, otherwise if checkbox is unchecked skip the file (FILE3.EXE) during installation. This is the code that i use, obviously the checkbox code is missing because i'm not able to do that [Files] Source: FILE1.EXE; DestDir: {app}; Source: FILE2.EXE; DestDir: {app}; Source: FILE3.EXE; DestDir: {app}; //OPTIONAL [Code] procedure ExitProcess(uExitCode: UINT); external '[email protected] stdcall'; var MainPage : TWizardPage; FolderToInstall : TEdit; InstallLocation : String; procedure CancelClick(Sender: TObject); begin if ExitSetupMsgBox then begin ExitProcess(0); end; end; procedure BrowseClick(Sender : TObject); var Dir : String; begin Dir := FolderToInstall.Text; if BrowseForFolder('Browse',Dir,false) then FolderToInstall.Text := Dir; WizardForm.DirEdit.Text := Dir; end; procedure InitializeWizard(); var LabelFolder : TLabel; begin WizardForm.ClientWidth:=ScaleX(550); WizardForm.ClientHeight:=ScaleY(250); WizardForm.Center; WizardForm.OuterNotebook.Hide; WizardForm.InnerNotebook.Hide; WizardForm.Bevel.hide; Wizardform.NextButton.top := 180; Wizardform.NextButton.Left := 470; WizardForm.NextButton.Height := 25; WizardForm.StatusLabel.Parent := WizardForm; WizardForm.StatusLabel.Left := 6; WizardForm.StatusLabel.Top := 206; WizardForm.FilenameLabel.Parent := WizardForm; WizardForm.FilenameLabel.Left := 87; WizardForm.FilenameLabel.Top := 206; WizardForm.FilenameLabel.Width := ScaleX(383); WizardForm.ProgressGauge.Parent := WizardForm; WizardForm.ProgressGauge.Left :=5; WizardForm.ProgressGauge.Top := 222; WizardForm.ProgressGauge.Width := ScaleX(460); MainPage := CreateCustomPage(wpWelcome,'',''); LabelFolder := TLabel.Create(MainPage); LabelFolder.Parent := WizardForm; LabelFolder.Top := 164; LabelFolder.Left := 6; LabelFolder.Caption := 'Directory:' FolderToInstall := TEdit.Create(MainPage); FolderToInstall.Parent := WizardForm; FolderToInstall.Top := 182; FolderToInstall.Left := 85; FolderToInstall.Width := 380; FolderToInstall.Text := WizardDirValue; FolderToInstall.ReadOnly := True; end;

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