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  • Can threads safely read variables set by VCL events?

    - by Tom1952
    Is it safe for a thread to READ a variable set by a Delphi VCL event? When a user clicks on a VCL TCheckbox, the main thread sets a boolean to the checkbox's Checked state. CheckboxState := CheckBox1.Checked; At any time, a thread reads that variable if CheckBoxState then ... It doesn't matter if the thread "misses" a change to the boolean, because the thread checks the variable in a loop as it does other things. So it will see the state change eventually... Is this safe? Or do I need special code? Is surrounding the read and write of the variable (in the thread and main thread respectively) with critical code calls necessary and sufficient? As I said, it doesn't matter if the thread gets the "wrong" value, but I keep thinking that there might be a low-level problem if one thread tries to read a variable while the main thread is in the middle of writing it, or vice versa. My question is similar to this one: http://stackoverflow.com/questions/1353096/cross-thread-reading-of-a-variable. (Also related to my previous question: http://stackoverflow.com/questions/2449183/using-entercriticalsection-in-thread-to-update-vcl-label)

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  • In Ruby, how can I initialize instance variables in new objects of core classes created from literal

    - by Ollie Saunders
    class Object attr_reader :foo def initialize @foo = 'bar' end end Object.new.foo # => 'bar' ''.foo # => nil //.foo # => nil [].foo # => nil I want them all to return 'bar' Am aware that you can do this already: class Object def foo 'bar' end end But I specifically want to initialize a state variable. Also note that this doesn't work. class String alias_method :old_init, :initialize def initialize(*args) super old_init(*args) end end class Object attr_reader :foo def initialize @foo = 'bar' super end end ''.foo # => nil Nor does this: class String attr_reader :foo def initialize @foo = 'bar' end end ''.instance_variables # => [] I'm beginning to think that this isn't actually possible.

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  • Are there any reasons to make all fields and variables final?

    - by Roman
    In my current project I noticed that all class fields and variable inside methods are declared with final modifier whenever it's possible. Just like here: private final XMLStreamWriter _xmlStreamWriter; private final Marshaller _marshaller; private final OutputStream _documentStream; private final OutputStream _stylesStream; private final XMLStreamWriter _stylesStreamWriter; private final StyleMerger _styleMerger; public DocumentWriter(PhysicalPackage physicalPackage) throws IOException { final Package pkg = new Package(physicalPackage); final Part wordDocumentPart = pkg.createPart( "/word/document.xml", "application/vnd.openxmlformats-officedocument.wordprocessingml.document.main+xml", "http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument"); // styles.xml final Pair<Part, String> wordStylesPart = wordDocumentPart.createRelatedPart(...); ... } Are there any reasons to do so? p.s. As I know project is not supposed to be multithreaded (at least I've heard nothing about it).

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  • Does `throw` cause stack variables (full types) to be freed from memory in C++?

    - by nbolton
    I'm pondering a question on Brainbench. I actually realised that I could answer my question easily by compiling the code, but it's an interesting question nonetheless, so I'll ask the question anyway and answer it myself shortly. Take a look at this snippet: The question considers what happens when we throw from a destructor (which causes terminate() to be called). It's become clear to me by asking the question that the memory is indeed freed and the destructor is called, but, is this before or after throw is called from foo? Perhaps the issue here is that throw is used while the stack is unwinding that is the problem... Actually this is slightly confusing.

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  • Using C code in c#

    - by karthik
    When i googled to find the way to change the window style i could find the code in "C" language How can i use the snippet below in my c# application, so that i can hide the Title Bar of external application ? I have not used "C" before.. //Finds a window by class name [DllImport("USER32.DLL")] public static extern IntPtr FindWindow(string lpClassName, string lpWindowName); //Sets a window to be a child window of another window [DllImport("USER32.DLL")] public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent); //Sets window attributes [DllImport("USER32.DLL")] public static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong); //Gets window attributes [DllImport("USER32.DLL")] public static extern int GetWindowLong(IntPtr hWnd, int nIndex); //assorted constants needed public static int GWL_STYLE = -16; public static int WS_CHILD = 0x40000000; //child window public static int WS_BORDER = 0x00800000; //window with border public static int WS_DLGFRAME = 0x00400000; //window with double border but no title public static int WS_CAPTION= WS_BORDER | WS_DLGFRAME; //window with a title bar /* This function sets the parent of the window with class ClassClass to the form/control the method is in. */ public void Reparent() { //get handle of parent form (.net property) IntPtr par = this.Handle; //get handle of child form (win32) IntPtr child = FindWindow("ClassClass", null); //set parent of child form SetParent(child, par); //get current window style of child form int style = GetWindowLong(child, GWL_STYLE); //take current window style and remove WS_CAPTION from it SetWindowLong(child, GWL_STYLE, (style & ~WS_CAPTION)); }

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  • R ggplot barplot; Fill based on two separate variables

    - by user1476968
    A picture says more than a thousand words. As you can see, my fill is based on the variable variable. Within each bar there is however multiple data entities (black borders) since the discrete variable complexity make them unique. What I am trying to find is something that makes each section of the bar more distinguishable than the current look. Preferable would be if it was something like shading. Here's an example (not the same dataset, since the original was imported): dat <- read.table(text = "Complexity Method Sens Spec MMC 1 L Alpha 50 20 10 2 M Alpha 40 30 80 3 H Alpha 10 10 5 4 L Beta 70 50 60 5 M Beta 49 10 80 6 H Beta 90 17 48 7 L Gamma 19 5 93 8 M Gamma 18 39 4 9 H Gamma 10 84 74", sep = "", header=T) library(ggplot2) library(reshape) short.m <- melt(dat) ggplot(short.m, aes(x=Method, y= value/100 , fill=variable)) + geom_bar(stat="identity",position="dodge", colour="black") + coord_flip()

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  • Why is this variables declared as private and also readonly?

    - by Sergio Tapia
    In the following code: public class MovieRepository : IMovieRepository { private readonly IHtmlDownloader _downloader; public MovieRepository(IHtmlDownloader downloader) { _downloader = downloader; } public Movie FindMovieById(string id) { var idUri = ...build URI...; var html = _downloader.DownloadHtml(idUri); return ...parse ID HTML...; } public Movie FindMovieByTitle(string title) { var titleUri = ...build URI...; var html = _downloader.DownloadHtml(titleUri); return ...parse title HTML...; } } I asked for something to review my code, and someone suggested this approach. My question is why is the IHtmlDownloader variable readonly?

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  • What is the cheapest non-colocation way to serve about 10 static files at a rate of 100 megabits per

    - by Mark Maunder
    I've looked at Amazon S3 and it costs roughly $4746 per month for 100 megabits/s (which translates into 31,640 Gigabytes of data transferred. That's at a rate of $0.15 per gig.) I haven't found a cheaper "cloud" option. I'm curious if there's any other cloud hosting option out there cheaper than S3. Uptime is not an issue because I can build failover for most things into the browser. e.g. I can use javascript to say "if the image didn't load then go to this other URL instead." FYI I'm currently using a colocation facility which is about 30% cheaper than S3 and I'm familiar with colo prices - so this question is really about "cloud" services and by that I mean services where I don't have to worry about the infrastructure.

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  • Does `throw` cause stack variables to be freed from memory in C++?

    - by nbolton
    I'm pondering a question on Brainbench. I actually realised that I could answer my question easily by compiling the code, but it's an interesting question nonetheless, so I'll ask the question anyway and answer it myself shortly. Take a look at this snippet: The question considers what happens when we throw from a destructor (which causes terminate() to be called). It's become clear to me by asking the question that the memory is indeed freed and the destructor is called, but, is this before or after throw is called from foo? Perhaps the issue here is that throw is used while the stack is unwinding that is the problem... Actually this is slightly confusing.

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  • How to remove the MenuBar of an application using windows API ?

    - by karthik
    I am using the below code to remove the Title Bar of an application, which is working perfectly for notepad. Now i want to remove the Menu Bar also. How to achieve it ? //Finds a window by class name [DllImport("USER32.DLL")] public static extern IntPtr FindWindow(string lpClassName, string lpWindowName); //Sets a window to be a child window of another window [DllImport("USER32.DLL")] public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent); //Sets window attributes [DllImport("USER32.DLL")] public static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong); //Gets window attributes [DllImport("USER32.DLL")] public static extern int GetWindowLong(IntPtr hWnd, int nIndex); [DllImport("user32.dll", EntryPoint = "FindWindow", SetLastError = true)] static extern IntPtr FindWindowByCaption(IntPtr ZeroOnly, string lpWindowName); //assorted constants needed public static int GWL_STYLE = -16; public static int WS_BORDER = 0x00800000; //window with border public static int WS_DLGFRAME = 0x00400000; //window with double border but no title public static int WS_CAPTION = WS_BORDER | WS_DLGFRAME; //window with a title bar public void WindowsReStyle() { Process[] Procs = Process.GetProcesses(); foreach (Process proc in Procs) { if (proc.ProcessName.StartsWith("notepad")) { IntPtr pFoundWindow = proc.MainWindowHandle; int style = GetWindowLong(pFoundWindow, GWL_STYLE); SetWindowLong(pFoundWindow, GWL_STYLE, (style & ~WS_CAPTION)); } } }

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  • How do I use my own debugger visualiser to edit variables runtime?

    - by C Sharper
    I'm writing my own debugger visualiser. All works great to show up to visualiser with the data. Now I add the code for more clearness: public class MyVisualiserObjectSource : VisualizerObjectSource { public override void GetData(object target, Stream outgoingData) { string data= target as string; var writer = new StreamWriter(outgoingData); writer.Write(data); writer.Flush(); } } public class MyVirtualizer : DialogDebuggerVisualizer { protected override void Show(IDialogVisualizerService windowService, IVisualizerObjectProvider objectProvider) { var streamReader = new StreamReader(objectProvider.GetData()); string data = streamReader.ReadToEnd(); using (var form = new MyVirtualizerForm(data)) { windowService.ShowDialog(form); } } } The string here is passed to the visualizer and show my own form. It works. But now I want to pass back the modified data from the form to the variable. How do I do that? Edit: I found out that I need to override the TransferData method in VisualizerObjectSource. But in the MSDN is no detail information about how I implement this correctly. Can someone help me please?

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  • Delphi Unit local variables - how to make each instance unique?

    - by Justin
    Ok, this, I'm sure is something simple that is easy to do. The problem : I've inherited scary spaghetti code and am slowly trying to better it when new features need adding - generally when a refactor makes adding the new feature neater. I've got a bunch of code I'm packing into a single unit which, in different places in the application, controls the same physical thing in the outside world. The control appears in several places in the application and operates slightly differently in each instance. What I've done is to create a unit with all of the features I need which I can simply drop, as a frame, into each form that requires it. Each form then uses the unit's interface methods to customise the behaviour for each instance. The problem within the problem : In the unit in question (the frame) I have a variable declared in the IMPLEMENTATION section - local to the unit. I also have a procedure, declared in the TYPE section which takes an argument and assigns that argument to the local variable in question - each form passes a unique variable to each instance of the frame/unit. What I want it to do is for each instance of the frame to keep its own version of that variable, different from the others, and use that to define how it operates. What seems to be happening, however, is that all instances are using the same value, even if I explicitly pass each instance a different variable. ie: Unit FlexibleUnit; interface uses //the uses stuff type TFlexibleUnit=class(TFrame) //declarations including procedure makeThisInstanceX(passMeTheVar:integer); private // public // end; implementation uses //the uses var myLocalVar; procedure makeThisInstanceX(passMeTheVar:integer); begin myLocalVar:=passMeTheVar; end; //other procedures using myLocalVar //etc to the end; Now somewhere in another Form I've dropped this Frame onto the Design pane, sometimes two of these frames on one Form, and have it declared in the proper places, etc. Each is unique in that : ThisFlexibleUnit : TFlexibleUnit; ThatFlexibleUnit : TFlexibleUnit; and when I do a: ThisFlexibleUnit.makeThisInstanceX(var1); //want to behave in way "var1" ThatFlexibleUnit.makeThisInstanceX(var2); //want to behave in way "var2" it seems that they both share the same variable "myLocalVar". Am I doing this wrong, in principle? If this is the correct method then it's a matter of debugging what I have (which is too huge to post) but if this is not correct in principle then is there a way to do what I am suggesting? Thanks in advance, Stack Overflow - you guys (and gals!) are legendary.

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  • In what circumstances are instance variables declared as '_var' in 'use fields' readonly?

    - by Pedro Silva
    I'm trying to understand the behavior of the fields pragma, which I find poorly documented, regarding fields prefixed with underscores. This is what the documentation has to say about it: Field names that start with an underscore character are made private to the class and are not visible to subclasses. Inherited fields can be overridden but will generate a warning if used together with the -w switch. This is not consistent with its actual behavior, according to my test, below. Not only are _-prefixed fields visible within a subclass, they are visible within foreign classes as well (unless I don't get what 'visible' means). Also, directly accessing the restricted hash works fine. Where can I find more about the behavior of the fields pragma, short of going at the source code? { package Foo; use strict; use warnings; use fields qw/a _b __c/; sub new { my ( $class ) = @_; my Foo $self = fields::new($class); $self->a = 1; $self->b = 2; $self->c = 3; return $self; } sub a : lvalue { shift->{a} } sub b : lvalue { shift->{_b} } sub c : lvalue { shift->{__c} } } { package Bar; use base 'Foo'; use strict; use warnings; use Data::Dumper; my $o = Bar->new; print Dumper $o; ##$VAR1 = bless({'_b' => 2, '__c' => 3, 'a' => 1}, 'Foo'); $o->a = 4; $o->b = 5; $o->c = 6; print Dumper $o; ##$VAR1 = bless({'_b' => 5, '__c' => 6, 'a' => 4}, 'Foo'); $o->{a} = 7; $o->{_b} = 8; $o->{__c} = 9; print Dumper $o; ##$VAR1 = bless({'_b' => 8, '__c' => 9, 'a' => 7}, 'Foo'); }

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  • Is it good practice to name variables differently when defining more than one function?

    - by John
    For example, in this simple function where fun1 takes as input two numbers, adds them together and passes them to function 2 for printing the output. var1_in is local to each function, so is it OK to use the name var1_in in both functions, or is it better practice to call them different things? fun1 <- function (var1_in, var2_in) { var3 = var1_in + var2_in fun2(var3) } fun2 <- function (var1_in) { var4 = var1_in print(var4) }

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  • Why is the compiler caching my "random" and NULLED variables?

    - by alex gray
    I am confounded by the fact that even using different programs (on the same machine) to run /compile, and after nilling the vaues (before and after) the function.. that NO MATTER WHAT.. I'll keep getting the SAME "random" numbers… each and every time I run it. I swear this is NOT how it's supposed to work.. I'm going to illustrate as simply as is possible… #import <Foundation/Foundation.h> int main(int argc, char *argv[]) { int rPrimitive = 0; rPrimitive = 1 + rand() % 50; NSNumber *rObject = nil; rObject = [NSNumber numberWithInt:rand() % 10]; NSLog(@"%i %@", rPrimitive, rObject); rPrimitive = 0; rObject = nil; NSLog(@"%i %@", rPrimitive, rObject); return 0; } Run it in TextMate: i686-apple-darwin11-llvm-gcc-4.2 8 9 0 (null) Run it in CodeRunner: i686-apple-darwin11-llvm-gcc-4.2 8 9 0 (null) Run it a million times, if you'd like. You can gues what it will always be. Why does this happen? Why oh why is this "how it is"?

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  • Inserting variables into a query string - it won't work!

    - by Jonesy
    Basically i have a query string that when i hardcode in the catalogue value its fine. when I try adding it via a variable it just doesn't pick it up. This works: Dim WaspConnection As New SqlConnection("Data Source=JURA;Initial Catalog=WaspTrackAsset_NROI;User id=" & ConfigurationManager.AppSettings("WASPDBUserName") & ";Password='" & ConfigurationManager.AppSettings("WASPDBPassword").ToString & "';") This doesn't: Public Sub GetWASPAcr() connection.Open() Dim dt As New DataTable() Dim username As String = HttpContext.Current.User.Identity.Name Dim sqlCmd As New SqlCommand("SELECT WASPDatabase FROM dbo.aspnet_Users WHERE UserName = '" & username & "'", connection) Dim sqlDa As New SqlDataAdapter(sqlCmd) sqlDa.Fill(dt) If dt.Rows.Count > 0 Then For i As Integer = 0 To dt.Rows.Count - 1 If dt.Rows(i)("WASPDatabase") Is DBNull.Value Then WASP = "" Else WASP = "WaspTrackAsset_" + dt.Rows(i)("WASPDatabase") End If Next End If connection.Close() End Sub Dim WaspConnection As New SqlConnection("Data Source=JURA;Initial Catalog=" & WASP & ";User id=" & ConfigurationManager.AppSettings("WASPDBUserName") & ";Password='" & ConfigurationManager.AppSettings("WASPDBPassword").ToString & "';") When I debug the catalog is empty in the query string but the WASP variable holds the value "WaspTrackAsset_NROI" Any idea's why? Cheers, jonesy

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  • Is it possible to have a Shared/Static Dependency Property?

    - by Matt H.
    [using VB.NET, but I can easily read C# code in responses] I have a class called QuestionClipboard with ALL shared methods/properties. I previously had a QuesitonClipboard.doesClipboardHaveContent function that returned true/false if there was a Object on my 'clipboard'. I'd prefer to implement a Dependency Property so I can allow this true/false value to participate in data binding. The "GetValue(dp as DependencyProperty)" method requires an object instance, which would mean that my Property CAN'T be shared! Here is what the code would look like in my perfect world... Of course, the word "Shared" before the property declaration renders this code useless. Private Shared clipboardHasContentPropertyKey As DependencyPropertyKey = DependencyProperty.RegisterReadOnly("clipboardHasContent", GetType(Boolean), GetType(QuestionClipboard), _ New PropertyMetadata(False, Nothing, New CoerceValueCallback(AddressOf coerceClipboardHasContent))) Private Shared clipboardHasContentProperty As DependencyProperty = clipboardHasContentPropertyKey.DependencyProperty Public SHARED Property clipboardHasContent As Boolean Get Return GetValue(clipboardHasContentProperty) End Get Set(ByVal value As Boolean) SetValue(value) End Set End Property

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