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  • How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

    - by Amir
    Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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  • getSelection() by Double Click or manual selection is not the same

    - by sanceray3
    Hi all, I allow me to ask a question, because I have a little probleme with an function which returns me the parent of a selection. $('input[type=button].btn_transform').click(function(){ var selectionObj = getSelected();//Function which gives me selection var theParent=selectionObj.anchorNode.parentNode; alert (theParent); }) For example with this sentence : "the cat is <strong>gray</strong>." If I select manually the word "gray" and click on my button, the function returns me [object HTMLSpanElement]. But if I select the same word by double clicking, the function returns me [object HTMLParagraphElement]. Do you know why ? Thanks a lot.

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  • Double-Escaped Unicode Javascript Issue

    - by Jeffrey Winter
    I am having a problem displaying a Javascript string with embedded Unicode character escape sequences (\uXXXX) where the initial "\" character is itself escaped as "&#92;" What do I need to do to transform the string so that it properly evaluates the escape sequences and produces output with the correct Unicode character? For example, I am dealing with input such as: "this is a &#92;u201ctest&#92;u201d"; attempting to decode the "&#92;" using a regex expression, e.g.: var out = text.replace('/&#92;/g','\'); results in the output text: "this is a \u201ctest\u201d"; that is, the Unicode escape sequences are displayed as actual escape sequences, not the double quote characters I would like.

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  • Watir: Need to double click on an element to open custom popup

    - by Namratha
    Hello, I am a newbie in WATIR. The problem I am facing is - The application I am testing has thumbnails (like Windows icons) placed on the page and I need to double click it. On doing that, an custom popup (ajax popup implemented in javascript) will open. The fire_event("ondblclick") is not working for me. I also tried 'click' twice but that too is not helping. Is there any other way of handling this? Your help is highly appreciated.

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  • split double in c wihout any libary

    - by DoomStone
    Hello I have a question for a c programmer out there, we have a tast at school to create a soft real time system in an operation system made by our teacher. Well that is all fine and dandy, we have chosen to create a system that calcuate how many unites of medicine a diabetic need based on his or hers blood sugar. It does not need to be correct just that we have the idea of a real time system :D But we have hit a little snag our formula for calculating the units of medicine is [blood sugar] * 1.2 But the only way we can send messages between processes is via a structure that contains 8 longs, but here is where my knowledge of c ends, we need for some way to split this double into 2 longs, example: the whole number in long 0 and the decimals in long 1 and then assemble it on the other side. But I have no idea who to do this, and therefore need a little help. We have tried but we do not have access to c standard libraries

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  • Forcing positive sign on double in .Net String.Format

    - by Max Yaffe
    Context: .Net, C# I want to print a complex number made from two doubles. The sign needs to show on the imaginary part. I'd like to use the default double formatting for each part to minimize the number of characters. I tried using String.Format("{0:+G;-G}{1:+G;-G}j", real, imaginary) but this ended up printing: "+G-Gj". Not quite what I wanted. Is there any way to do this using the G specifier or do I need to do a custom format which would sacrifice auto-switching the exponent, e.g. {1:+#.######e###;-#.######e###}j"

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  • Loss of precision - int -> float or double

    - by stan
    I have an exam question i am revising for and the question is for 4 marks "In java we can assign a int to a double or a float". Will this ever loose infromation and why? I have put that because ints are normally of fixed length or size - the precision for sotring data is finite, where storing information in floating point can be infinite, essentially we loose infromation because of this Now i am a little sketchy as to whetehr or not i am hitting the right areas here. I very sure it will loose precision but i cant exactly put my finger on why. Can i getsome help please Thanks

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  • How do you set a double value to a "non-value"

    - by Ankur
    I have two double data elements in an object. Sometimes they are set with a proper value and sometimes not. When the form field from which they values are received is not filled I want to set them to some value that tells me, during the rest of the code that the form fields were left empty. I can't set the values to null as that gives an error, is there some way I can make them 'Undefined'. PS. Not only am I not sure that this is possible, it might not also make sense. But if there is some best practice for such a situation I would be keen to hear it.

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  • Double # showing 0 on android

    - by Dave
    I'm embarrassed to ask this question, but after 45 minutes of not finding a solution I will resort to public humiliation. I have a number that is being divided by another number and I'm storing that number in a double variable. The numbers are randomly generated, but debugging the app shows that both numbers are in fact being generated. Lets just say the numbers are 476 & 733. I then take the numbers and divide them to get the percentage 476/733 = .64 I then print out the variable and it's always set to 0. I've tried using DecimalFormat and NumberFormat. No matter what I try though it always says the variable is 0. I know there is something simple that I'm missing, I just can't find it =/.

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  • Printing double variable contents

    - by Adil
    I tried following code snippet and output is surprising me: #include <stdio.h> #include <math.h> int main() { double num; unsigned char ch; ch = 19; num = 1.0E+20 ; num += ch * 1.0E+18; printf("E18 = %lf \n",num); printf("E18 = %e \n",num); num = 11.0E+21 ; num += ch * 1.0E+19; printf("E19 = %lf <------\n",num); printf("E19 = %e <------\n",num); num = 11.0E+22 ; num += ch * 1.0E+20; printf("E20 = %lf\n",num); printf("E20 = %e\n",num); num = 11.0E+23 ; num += ch * 1.0E+21; printf("E21 = %lf\n",num); printf("E21 = %e\n",num); num = 11.0E+24 ; num += ch * 1.0E+22; printf("E22 = %lf <------\n",num); printf("E22 = %e <------\n",num); return 0; } The output of the program: E18 = 119000000000000000000.000000 E18 = 1.190000e+20 E19 = 11190000000000000524288.000000 <------ E19 = 1.119000e+22 <------ E20 = 111900000000000001048576.000000 E20 = 1.119000e+23 E21 = 1119000000000000044040192.000000 E21 = 1.119000e+24 E22 = 11189999999999999366660096.000000 <------ E22 = 1.119000e+25 <------ Why the data corrupted when printed while in exponent form its OK

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  • Dangling pointers and double free

    - by user151410
    After some painful experiences, I understand the problem of dangling pointers and double free. I am seeking proper solutions. aStruct has a number of fields including other arrays. aStruct *A=NULL, *B = NULL; A = (aStruct*) calloc(1, sizeof(sStruct)); B = A; free_aStruct(A); ... //bunch of other code in various places. ... free_aStruct(B); Is there any way to write free_aStruct(X) so that free_aStruct(B) exists gracefully?? void free_aStruct(aStruct *X){ if (X ! = NULL){ if (X->a != NULL){free(X->a); x->a = NULL;} free(X); X = NULL; } } Doing above only sets A = NULL when free_aStruct(A); is called. B is now dangling. How can this situation be avoided / remedied? Is reference counting the only viable solution? or, are there other "defensive" free approaches, to prevent free_aStruct(B); from exploding? Thanks, Russ

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  • ASP.Net - Help with datagrid/checkboxes/double submit

    - by Gareth D
    We have a simple datagrid. Each row has a checkbox. The checkbox is set to autopostback, and the code-behind has an event handler for the checkbox check-changed event. This all works as expected, nothing complicated. However, we want to disable the checkboxes as soon as one is checked to prevent a double submit i.e. check box checked, all checkboxes are disabled via client side javascript, form submitted. To achieve this I we are injecting some code into the onclick event as follows (note that the alert is just for testing!): Protected Sub DgAccounts_ItemCreated(ByVal sender As System.Object, ByVal e As System.Web.UI.WebControls.DataGridItemEventArgs) Handles DgAccounts.ItemCreated If e.Item.ItemType = ListItemType.Item Or e.Item.ItemType = ListItemType.AlternatingItem Then Dim chk As CheckBox = CType(e.Item.FindControl("chkItemChecked"), CheckBox) chk.Attributes.Add("onclick", "alert('fired ...');DisableAllDataGridCheckBoxes();") End If End Sub When inspecting the source of the rendered page we get the following: <input id="DgAccounts__ctl2_chkItemChecked" type="checkbox" name="DgAccounts:_ctl2:chkItemChecked" onclick="alert('fired ...');DisableAllDataGridCheckBoxes();setTimeout('__doPostBack(\'DgAccounts$_ctl2$chkItemChecked\',\'\')', 0)" language="javascript" /> It all appears in order, however the server side event does not fire – I believe this is due to the checkbox being disabled, as if we just leave the alert in and remove the call to disable the checkbox it all works fine. Can I force the check-changed event to fire even though the check box is disabled?

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  • Efficiency of Java "Double Brace Initialization"?

    - by Jim Ferrans
    In Hidden Features of Java the top answer mentions Double Brace Initialization, with a very enticing syntax: Set<String> flavors = new HashSet<String>() {{ add("vanilla"); add("strawberry"); add("chocolate"); add("butter pecan"); }}; This idiom creates an anonymous inner class with just an instance initializer in it, which "can use any [...] methods in the containing scope". Main question: Is this as inefficient as it sounds? Should its use be limited to one-off initializations? (And of course showing off!) Second question: The new HashSet must be the "this" used in the instance initializer ... can anyone shed light on the mechanism? Third question: Is this idiom too obscure to use in production code? Summary: Very, very nice answers, thanks everyone. On question (3), people felt the syntax should be clear (though I'd recommend an occasional comment, especially if your code will pass on to developers who may not be familiar with it). On question (1), The generated code should run quickly. The extra .class files do cause jar file clutter, and slow program startup slightly (thanks to coobird for measuring that). Thilo pointed out that garbage collection can be affected, and the memory cost for the extra loaded classes may be a factor in some cases. Question (2) turned out to be most interesting to me. If I understand the answers, what's happening in DBI is that the anonymous inner class extends the class of the object being constructed by the new operator, and hence has a "this" value referencing the instance being constructed. Very neat. Overall, DBI strikes me as something of an intellectual curiousity. Coobird and others point out you can achieve the same effect with Arrays.asList, varargs methods, Google Collections, and the proposed Java 7 Collection literals. Newer JVM languages like Scala, JRuby, and Groovy also offer concise notations for list construction, and interoperate well with Java. Given that DBI clutters up the classpath, slows down class loading a bit, and makes the code a tad more obscure, I'd probably shy away from it. However, I plan to spring this on a friend who's just gotten his SCJP and loves good natured jousts about Java semantics! ;-) Thanks everyone!

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  • Error codes for C++

    - by billy
    #include <iostream> #include <iomanip> using namespace std; //Global constant variable declaration const int MaxRows = 8, MaxCols = 10, SEED = 10325; //Functions Declaration void PrintNameHeader(ostream& out); void Fill2DArray(double ary[][MaxCols]); void Print2DArray(const double ary[][MaxCols]); double GetTotal(const double ary[][MaxCols]); double GetAverage(const double ary[][MaxCols]); double GetRowTotal(const double ary[][MaxCols], int theRow); double GetColumnTotal(const double ary[][MaxCols], int theRow); double GetHighestInRow(const double ary[][MaxCols], int theRow); double GetLowestInRow(const double ary[][MaxCols], int theRow); double GetHighestInCol(const double ary[][MaxCols], int theCol); double GetLowestInCol(const double ary[][MaxCols], int theCol); double GetHighest(const double ary[][MaxCols], int& theRow, int& theCol); double GetLowest(const double ary[][MaxCols], int& theRow, int& theCol); int main() { int theRow; int theCol; PrintNameHeader(cout); cout << fixed << showpoint << setprecision(1); srand(static_cast<unsigned int>(SEED)); double ary[MaxRows][MaxCols]; cout << "The seed value for random number generator is: " << SEED << endl; cout << endl; Fill2DArray(ary); Print2DArray(ary); cout << " The Total for all the elements in this array is: " << setw(7) << GetTotal(ary) << endl; cout << "The Average of all the elements in this array is: " << setw(7) << GetAverage(ary) << endl; cout << endl; cout << "The sum of each row is:" << endl; for(int index = 0; index < MaxRows; index++) { cout << "Row " << (index + 1) << ": " << GetRowTotal(ary, theRow) << endl; } cout << "The highest and lowest of each row is: " << endl; for(int index = 0; index < MaxCols; index++) { cout << "Row " << (index + 1) << ": " << GetHighestInRow(ary, theRow) << " " << GetLowestInRow(ary, theRow) << endl; } cout << "The highest and lowest of each column is: " << endl; for(int index = 0; index < MaxCols; index++) { cout << "Col " << (index + 1) << ": " << GetHighestInCol(ary, theRow) << " " << GetLowestInCol(ary, theRow) << endl; } cout << "The highest value in all the elements in this array is: " << endl; cout << GetHighest(ary, theRow, theCol) << "[" << theRow << "]" << "[" << theCol << "]" << endl; cout << "The lowest value in all the elements in this array is: " << endl; cout << GetLowest(ary, theRow, theCol) << "[" << theRow << "]" << "[" << theCol << "]" << endl; return 0; } //Define Functions void PrintNameHeader(ostream& out) { out << "*******************************" << endl; out << "* *" << endl; out << "* C.S M10A Spring 2010 *" << endl; out << "* Programming Assignment 10 *" << endl; out << "* Due Date: Thurs. Mar. 25 *" << endl; out << "*******************************" << endl; out << endl; } void Fill2DArray(double ary[][MaxCols]) { for(int index1 = 0; index1 < MaxRows; index1++) { for(int index2= 0; index2 < MaxCols; index2++) { ary[index1][index2] = (rand()%1000)/10; } } } void Print2DArray(const double ary[][MaxCols]) { cout << " Column "; for(int index = 0; index < MaxCols; index++) { int column = index + 1; cout << " " << column << " "; } cout << endl; cout << " "; for(int index = 0; index < MaxCols; index++) { int column = index +1; cout << "----- "; } cout << endl; for(int index1 = 0; index1 < MaxRows; index1++) { cout << "Row " << (index1 + 1) << ":"; for(int index2= 0; index2 < MaxCols; index2++) { cout << setw(6) << ary[index1][index2]; } } } double GetTotal(const double ary[][MaxCols]) { double total = 0; for(int theRow = 0; theRow < MaxRows; theRow++) { total = total + GetRowTotal(ary, theRow); } return total; } double GetAverage(const double ary[][MaxCols]) { double total = 0, average = 0; total = GetTotal(ary); average = total / (MaxRows * MaxCols); return average; } double GetRowTotal(const double ary[][MaxCols], int theRow) { double sum = 0; for(int index = 0; index < MaxCols; index++) { sum = sum + ary[theRow][index]; } return sum; } double GetColumTotal(const double ary[][MaxCols], int theCol) { double sum = 0; for(int index = 0; index < theCol; index++) { sum = sum + ary[index][theCol]; } return sum; } double GetHighestInRow(const double ary[][MaxCols], int theRow) { double highest = 0; for(int index = 0; index < MaxCols; index++) { if(ary[theRow][index] > highest) highest = ary[theRow][index]; } return highest; } double GetLowestInRow(const double ary[][MaxCols], int theRow) { double lowest = 0; for(int index = 0; index < MaxCols; index++) { if(ary[theRow][index] < lowest) lowest = ary[theRow][index]; } return lowest; } double GetHighestInCol(const double ary[][MaxCols], int theCol) { double highest = 0; for(int index = 0; index < MaxRows; index++) { if(ary[index][theCol] > highest) highest = ary[index][theCol]; } return highest; } double GetLowestInCol(const double ary[][MaxCols], int theCol) { double lowest = 0; for(int index = 0; index < MaxRows; index++) { if(ary[index][theCol] < lowest) lowest = ary[index][theCol]; } return lowest; } double GetHighest(const double ary[][MaxCols], int& theRow, int& theCol) { theRow = 0; theCol = 0; double highest = ary[theRow][theCol]; for(int index = 0; index < MaxRows; index++) { for(int index1 = 0; index1 < MaxCols; index1++) { double highest = 0; if(ary[index1][theCol] > highest) { highest = ary[index][index1]; theRow = index; theCol = index1; } } } return highest; } double Getlowest(const double ary[][MaxCols], int& theRow, int& theCol) { theRow = 0; theCol = 0; double lowest = ary[theRow][theCol]; for(int index = 0; index < MaxRows; index++) { for(int index1 = 0; index1 < MaxCols; index1++) { double lowest = 0; if(ary[index1][theCol] < lowest) { lowest = ary[index][index1]; theRow = index; theCol = index1; } } } return lowest; } . 1>------ Build started: Project: teddy lab 10, Configuration: Debug Win32 ------ 1>Compiling... 1>lab 10.cpp 1>c:\users\owner\documents\visual studio 2008\projects\teddy lab 10\teddy lab 10\ lab 10.cpp(46) : warning C4700: uninitialized local variable 'theRow' used 1>c:\users\owner\documents\visual studio 2008\projects\teddy lab 10\teddy lab 10\ lab 10.cpp(62) : warning C4700: uninitialized local variable 'theCol' used 1>Linking... 1> lab 10.obj : error LNK2028: unresolved token (0A0002E0) "double __cdecl GetLowest(double const (* const)[10],int &,int &)" (?GetLowest@@$$FYANQAY09$$CBNAAH1@Z) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ) 1> lab 10.obj : error LNK2019: unresolved external symbol "double __cdecl GetLowest(double const (* const)[10],int &,int &)" (?GetLowest@@$$FYANQAY09$$CBNAAH1@Z) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ) 1>C:\Users\owner\Documents\Visual Studio 2008\Projects\ lab 10\Debug\ lab 10.exe : fatal error LNK1120: 2 unresolved externals 1>Build log was saved at "file://c:\Users\owner\Documents\Visual Studio 2008\Projects\ lab 10\teddy lab 10\Debug\BuildLog.htm" 1>teddy lab 10 - 3 error(s), 2 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • Binary files printing and desired precision

    - by yCalleecharan
    Hi, I'm printing a variable say z1 which is a 1-D array containing floating point numbers to a text file so that I can import into Matlab or GNUPlot for plotting. I've heard that binary files (.dat) are smaller than .txt files. The definition that I currently use for printing to a .txt file is: void create_out_file(const char *file_name, const long double *z1, size_t z_size){ FILE *out; size_t i; if((out = _fsopen(file_name, "w+", _SH_DENYWR)) == NULL){ fprintf(stderr, "***> Open error on output file %s", file_name); exit(-1); } for(i = 0; i < z_size; i++) fprintf(out, "%.16Le\n", z1[i]); fclose(out); } I have three questions: Are binary files really more compact than text files?; If yes, I would like to know how to modify the above code so that I can print the values of the array z1 to a binary file. I've read that fprintf has to be replaced with fwrite. My output file say dodo.dat should contain the values of array z1 with one floating number per line. I have %.16Le up in my code but I think that %.15Le is right as I have 15 precision digits with long double. I have put a dot (.) in the width position as I believe that this allows expansion to an arbitrary field to hold the desired number. Am I right? As an example with %.16Le, I can have an output like 1.0047914240730432e-002 which gives me 16 precision digits and the width of the field has the right width to display the number correctly. Is placing a dot (.) in the width position instead of a width value a good practice? Thanks a lot...

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  • Single and Double Jump with single button.

    - by Asad
    I want to make Single Jump on Single Tap and Double Jump on Double Tap. My problem is that if I make double Tap on ground then it’s fine but if I make first Tap on ground and second Tap in Air then Player gain more height then usual As in image 1. I want to Make my jump like in Image 2, No matter from which point user gives second Tap, player Always get a specific height. I Used both Impulse and Linear velocity to make Jump but my problem did not solved.

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  • Flash Double-click an externally loaded SWF

    - by Trist
    OK. I've got a class (which extends MovieClip) that loads in an external SWF (made in pdf2swf). That is added to another class which has declared doubleClickEnabled = true and I'm listening for DOUBLE_CLICK events. Problem is when the SWF is loaded my code picks up no DOUBLE_CLICK events, only CLICK events. I've tried it without adding the SWF to the stage and it does pick up DOUBLE_CLICK events. Anybody come across this before? class ParentClass{ ... public function ParentClass(){ ... mcToLoadSWF = new MovieClip(); addChild(mcToLoadSWF); doubleClickEnabled = true; addEventListener(MouseEvent.DOUBLE_CLICK, doubleClickHandler); ... } } I've also tried adding the event listener to the mcToLoadSWF as well. No dice. Cheers Tristian

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  • C# define string format of double/floats to be US english by default

    - by neil
    Hi, I have got several thousands of lines of a web application source code, initially written on a US development system, to maintain. It makes heavy use of SQL statement strings, which are combined on the fly, e.g. string SQL = "select * from table where double_value = " + Math.Round(double_value, 2); Don't comment on bad programming style, that doesn't help me in this case :) The cruix: My system uses a German locale, which in turn leads to wrong SQL statements, like this: "select * from table where double_value = 15,5" (Note the comma as decimal separator instead of a point). Question: What is the most "elegant" way to change the locale of the web app in this case) to US or UK in order to prevent being forced to change and inspect every single line of code? .net 3.5 is not an option (would give me the chance to overwrite ToString() in an extension class) Kind regards

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  • Ajax Double Call

    - by Lordareon
    with this function <script type="text/javascript"> function ajaxcall(div, page) { if (window.XMLHttpRequest) {xmlhttp=new XMLHttpRequest();} else { xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 && xmlhttp.status==200) { document.getElementById(div).innerHTML=xmlhttp.responseText; } } xmlhttp.open("GET",page,true); xmlhttp.send(); } </script> i use my ajax. But in the page i call 2 times this function: <script type="text/javascript">ajaxcall("menu", "perfil.php");</script> <script type="text/javascript">ajaxcall('mapadiv', "map2.php");</script> But happens that only one of them works, if i remove one the other works. What im doing wrong? Thanks!

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