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• How to preserve data integrity while minimizing the transmission size

  - by user1500578

  we have sensors in the wild that send their data to a server every day via TCP/IP, either through 3G or through satellite for the physical layer. The sensors can automatically switch from one to the other depending on their location and the quality of the signal with the local 3G operator. Given that the 3G and satellite communications are very expensive, we want to minimize the amount of data to send. But also, we want to protect ourselves from lost data. What would be the best strategy to ensure with reasonable certainty that the integrity of our data is preserved, while minimizing the amount of redundancy, i.e the amount of data transmitted ? I've read about the zfec codec, but I'm not sure if we need to transmit all the chunks, or if we need to send a hash code along each chunk.

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• Floating point equality and tolerances

  - by doron

  Comparing two floating point number by something like a_float == b_float is looking for trouble since a_float / 3.0 * 3.0 might not be equal to a_float due to round off error. What one normally does is something like fabs(a_float - b_float) < tol. How does one calculate tol? Ideally tolerance should be just larger than the value of one or two of the least significant figures. So if the single precision floating point number is use tol = 10E-6 should be about right. However this does not work well for the general case where a_float might be very small or might be very large. How does one calculate tol correctly for all general cases? I am interested in C or C++ cases specifically.

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• State pattern: Why doesn't the context class implement or inherit the State abstract interface/class

  - by Ricket

  I'm reading about the State pattern. I have only just begun, so of course I begin by reading the entire Wikipedia article on it. I noticed that both of the examples in the article have some base abstract class or Java interface for a generic State's methods/functions. Then there are some states which inherit from the base and implement those methods/functions in different ways. Then there's a Context class which has a private member of type State and which, at any time, can be equal to an instance of one of the implementations. That context class also implements the same methods, and passes them onto the current state instance, and then has an additional method to change the state (or depending on design I understand the change of state could be a reaction to one of the implemented methods). Why doesn't this context class specifically "extend" or "implement" the generic State base class/interface?

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• Can "\Device\NamedPipe\\Win32Pipes" handles cause "Too many open files" error?

  - by Igor Oks

  Continuing from this question: When I am trying to do fopen on Windows, I get a "Too many open files" error. I tried to analyze, how many open files I have, and seems like not too much. But when I executed Process Explorer, I noticed that I have many open handles with similar names: "\Device\NamedPipe\Win32Pipes.00000590.000000e2", "\Device\NamedPipe\Win32Pipes.00000590.000000e3", etc. I see that the number of these handles is exactly equal to the number of the iterations that my program executed, before it returned "Too many open files" and stopped. I am looking for an answer, what are these handles, and could they actually cause the "Too many open files" error? In my program I am loading files from remote drive, and I am creating TCP/IP connections. Could one of these operations create these handles?

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• Copy constructor demo (crashing... case 2)

  - by AKN

  Please have a glance at this program: class CopyCon { public: char *name; CopyCon() { name = new char[20]; name = "Hai";//_tcscpy(name,"Hai"); } CopyCon(const CopyCon &objCopyCon) { name = new char[_tcslen(objCopyCon.name)+1]; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete[] name; name = NULL; } } }; int main() { CopyCon obj1; CopyCon obj2(obj1); cout<<obj1.name<<endl; cout<<obj2.name<<endl; } This program crashes on execution. Error: "Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse)" If I assign "Hai" to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign "Hai" to name, its working perfectly. Can some one explain why so?

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• How do I check the validity of the Canadian Social Insurance Number in C#?

  - by user518307

  I've been given the assignment to write an algorithm in C# that checks the validity of a Canadian Social Insurance Number (SIN). Here are the steps to validate a SIN. Given an example Number: 123 456 782 Remove the check digit (the last digit): 123456782 Extract the even digits (2,4,6,8th digith): 12345678 Double them: 2 4 6 8 | | | | v v v v 4 8 12 16 Add the digits together: 4+8+1+2+1+6 = 22 Add the Odd placed digits: 1+3+5+7 = 16 Total : 38 Validity Algorithm If the total is a multiple of 10, the check digit should be zero. Otherwise, Subtract the Total from the next highest multiple of 10 (40 in this case) The check digit for this SIN must be equal to the difference of the number and the totals from earlier (in this case, 40-38 = 2; check digit is 2, so the number is valid) I'm lost on how to actually implement this in C#, how do I do this?

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• Excel VBA to check autofilter for data

  - by cav719

  I need help checking for autofiltered rows not including the header. I want it to give a message box "No records found." then exit sub or continue with copy paste if there are rows beyond the header row. I know I need an If/Else entry after the filter to check for data but I'm having trouble figuring how to check. This code is being done from a UserForm I created. Here is my script: Private Sub Searchbycompanyfield_Click() If CompanyComboBox1.Value = "" Then MsgBox "Please enter a Company to begin search." Exit Sub End If ActiveSheet.Range("$A:$H").AutoFilter Field:=1, Criteria1:=EQDataEntry.CompanyComboBox1.Value, Operator:=xlOr Cells.Select Selection.Copy Sheets("Sheet2").Select Range("A5").Select ActiveSheet.Paste Call MessageBoxYesOrNoMsgBox End Sub Any help would be greatly appreciated.

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• Storing multiple checkbox values in database

  - by Madjokr

  Hi, I want to store multiple column values in table.Lets take a example .. What are your favourite colors? the choices can be red,blue,green, orange. So lets assume, the user selects atleast 2 values. Is there any way to store the multiple values in table. I have implemented by concatinating choices of users in a column in the table. I later found that it is a bad practise. Currently i can think of using Bitwise operator and habtm. What are the different ways for storing multiple choices values in table? If I am implementing in rails, What is the best way to implement this with OOP concepts? Is there any builtin options in rails?

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• How to pass jQuery variable with AJAX to PHP page

  - by Walden

  Trying to pass the variable "flickrurl" to a PHP page with jQuery/ajax. It works when using a plain text string and not the variable. Am I assigning the variable properly? see the full code in action here: http://is.gd/c9ytI $trash.droppable({ accept: '#gallery > li', activeClass: 'ui-state-highlight', drop: function(ev, ui) { deleteImage(ui.draggable); //set variable equal to src of image tag in #gallery > li var $flickrurl = $item.find('img').attr("src"); //pass variable to php page $.post("updateDB.php", $flickrurl ); } });

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• How To Get A Field Value Based On The Max Of Another Field In VFP v8.0

  - by DaveB

  So, I have a table and I want to get the value from one field in the record with the greatest DateTime() value in another field and where still another field is equal to a certain value. Example data: Balance Created MeterNumber 7924.252 02/02/2010 10:31:48 AM 2743800 7924.243 02/02/2010 11:01:37 AM 2743876 7924.227 02/02/2010 03:55:50 PM 2743876 I want to get the balance for a record with the greatest created datetime for a specific meter number. In VFP 7 I can use: SELECT a.balance ,MAX(a.created) FROM MyTable a WHERE a.meternumber = '2743876' But, in the VFP v8.0 OleDb driver I am using in my ASP.NET page I must conform to VFP 8 which says you must have a GROUP BY listing each non aggregate field listed in the SELECT. This would return a record for each balance if I added GROUP BY a.balance to my query. Yes, I could issue a SET ENGINEBEHAVIOR 70 but I wanted to know if this could be done without having to revert to a previous version?

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• Date Comparision using Java

  - by Lakshman

  To Date (User Input - format - MM/dd/YYYY) Current Date. I need to compare the current date with To Date. Note: currenet date i get using Date currDt = new Date(). I have to display a report only when the toDate is equal to or more than currentDate. How to compare both the date. [ToDate is a String type i always get in mm/dd/yyyy] Current Date is Date currDt = new Date(). How to compare both the dates. need snippet.

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• ruby on rails: How do I access variable data in a url parameter passed to a model?

  - by bandhunt

  I have a variable called "account_type" passed from a rails form and need to access the value in the corresponding model. I can check if :account_type exists as a symbol, but where does the stored data come into play? Is there something I need to do in the controller? This code gives an undefined method 'account_type' error. validates_format_of :name, :with => /^[a-z0-9_]+$/i, :on => :create if account_type == 2 If I use a symbol then it doesn't give an error, but a symbol will never equal 2 validates_format_of :name, :with => /^[a-z0-9_]+$/i, :on => :create if :account_type == 2 It's confusing that you can validate the format of a symbol (like :name above) when :name only seems to be a reference with nothing stored in it. Thanks!

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• VBA: How to refer to the right worksheet

  - by stanigator

  Sub Macro1() ' ' Macro1 Macro ' ' Worksheets("Drop-down").Select n = Cells(1, 1).End(xlDown).Row For i = 1 To n ActiveSheet.Cells(i, 2).Select If Worksheets("Misc").Cells(2, i).Value <> "" Then If Worksheets("Misc").Cells(3, i).Value <> "" Then Set validationRange = Range(Worksheets("Misc").Cells(2, i), Worksheets("Misc").Cells(2, i).End(xlDown)) Else Set validationRange = Worksheets("Misc").Cells(2, i) End If With Selection.Validation .Delete .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _ xlBetween, Formula1:=validationRange.Address .IgnoreBlank = True .InCellDropdown = True .InputTitle = "" .ErrorTitle = "" .InputMessage = "" .ErrorMessage = "" .ShowInput = True .ShowError = True End With End If Next i End Sub The lines after ActiveSheet.Cells(i,2).select within the for loop is not referring to the correct worksheet I want when I rechecked the settings for the validation drop-down menu. What is the easiest way of correcting this setback? Thanks in advance.

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• Conversion of Linq expressions

  - by Arnis L.

  I'm not sure how exactly argument what I'm trying to achieve, therefore - wrote some code: public class Foo{ public Bar Bar{get;set;} } public class Bar{ public string Fizz{get;set;} } public class Facts{ [Fact] public void fact(){ Assert.Equal(expectedExp(),barToFoo(barExp())); } private Expression<Func<Foo,bool>> expectedExp(){ return f=>f.Bar.Fizz=="fizz"; } private Expression<Func<Bar,bool>> barExp(){ return b=>b.Fizz=="fizz"; } private Expression<Func<Foo,bool>> barToFoo (Expression<Func<Bar,bool>> barExp){ return Voodoo(barExp); //<-------------------------------------------??? } } Is this even possible?

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• std::map default value for build-in type

  - by Qifa Zhao

  Recently, I was confused by the std::map operator[] function. In the MSDN library, it says: "If the argument key value is not found, then it is inserted along with the default value of the data type." I tryed to search much more exactly explanation for this issue. For example here: std::map default value In this page, Michael Anderson said that "the default value is constructed by the default constructor(zero parameter constructor)". Now my quest comes to this:"what the default value for the build-in type?". Was it compiler related? Or is there a standard for this issue by the c++ stardard committee? I did a test on visual studio 2008 for the "int" type, and found the "int" type is construted with the value 0.

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• Intersection of two querysets in django

  - by unagimiyagi

  Hello, I can't do an AND on two querysets. As in, q1 & q2. I get the empty set and I do not know why. I have tested this with the simplest cases. I am using django 1.1.1 I have basically objects like this: item1 name="Joe" color = "blue" item2 name="Jim" color = "blue" color = "white" item3 name="John" color = "red" color = "white" Is there something weird about having a many-to-many relationship or what am I missing? queryset1 = Item.objects.filter(color="blue") this gives (item1, item2) queryset2 = Item.objects.filter(color="white") this gives (item2, item3) queryset1 & queryset2 gives me the empty set [] The OR operator works fine (I'm using "|" ) Why is this so?

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• Run time error '3075' in Access 2007

  - by Thys

  I am getting the following error when I try to open a report in Access 2007. The code works fine in Access 2003. run time error '3075' Syntax error (missing operator) in query expression '[COUNTRY_ID]=' here is the code giving the error... How could I fix this? Private Sub List25_Click() Combo20.SetFocus 'DoCmd.FindRecord List25.ItemData(List25.ListIndex) Forms![Country Rate Administration].Filter = "[COUNTRY_ID]=" & List25.ItemData(List25.ListIndex) Forms![Country Rate Administration].FilterOn = True End Sub Thansk in advance for your help!

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• Tips for optimizing C#/.NET programs

  - by Bob

  It seems like optimization is a lost art these days. Wasn't there a time when all programmers squeezed every ounce of efficiency from their code? Often doing so while walking 5 miles in the snow? In the spirit of bringing back a lost art, what are some tips that you know of for simple (or perhaps complex) changes to optimize C#/.NET code? Since it's such a broad thing that depends on what one is trying to accomplish it'd help to provide context with your tip. For instance: When concatenating many strings together use StringBuilder instead. If you're only concatenating a handful of strings it's ok to use the + operator. Use string.Compare to compare 2 strings instead of doing something like string1.ToLower() == string2.ToLower()

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• How does sizeof calculate the size of structures

  - by Gearoid Murphy

  I know that a char and an int are calculated as being 8 bytes on 32 bit architectures due to alignment, but I recently came across a situation where a structure with 3 shorts was reported as being 6 bytes by the sizeof operator. Code is as follows: #include <iostream> using namespace std ; struct IntAndChar { int a ; unsigned char b ; }; struct ThreeShorts { unsigned short a ; unsigned short b ; unsigned short c ; }; int main() { cout<<sizeof(IntAndChar)<<endl; // outputs '8' cout<<sizeof(ThreeShorts)<<endl; // outputs '6', I expected this to be '8' return 0 ; } Compiler : g++ (Debian 4.3.2-1.1) 4.3.2. This really puzzles me, why isn't alignment enforced for the structure containing 3 shorts?

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• Interesting interview question. .Net

  - by rahul

  Coding Problem NumTrans There is an integer K. You are allowed to add to K any of its divisors not equal to 1and K. The same operation can be applied to the resulting number and so on. Notice that starting from the number 4, we can reach any composite number by applying several such operations. For example, the number 24 can be reached starting from 4 using 5 operations: 468121824 You will solve a more general problem. Given integers n and m, return the minimal number of the described operations necessary to transform n into m. Return -1 if m can't be obtained from n. Definition Method signature: int GetLeastCount (int n, int m) Constraints N will be between 4 and 100000, inclusive. M will be between N and 100000, inclusive. Examples 1) 4 576 Returns: 14 The shortest order of operations is: 468121827365481108162243324432576 2) 8748 83462 Returns: 10 The shortest order of operations is: 874813122196832624439366590497873283106834488346083462 3) 4 99991 Returns: -1 The number 99991 can't be obtained because it’s prime!

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• Strange Google Maps v3 geocode behavior when a quote is in the address

  - by AlexV

  See my test page. When on the page, click the top left button "Geocode". If you are in Firefox, geocoder.geocode() will have it's status equal to ERROR (and pop an alert after a few seconds). In Internet Explorer (at least 7), everything is fine and the marker is added to the map. If you remove the quote from the address (l'Assomption -- lAssomption), everything execute fine in Firefox. Now with my question: how a quote can "crash" the Google Maps V3 API only in Firefox!?

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• Constructing T-SQL WHERE condition at runtime

  - by Nickson

  I would like to implement a search function where a user passes all the arguments to the "WHERE" clause at runtime. For example in query below, SELECT Col1, Col2, Col3, Col4 FROM MyTable WHERE Col2 = John 1.Now what i want is to give the user a dropdownlist of columnns such that the user selects a column to search by at runtime Also instead of precoding Col2 = John, i want the user to choose their own operator at runtime(such as choosing between =, <, <, <, LIKE, IN) i basically want to contruct a query like SELECT Col1, Col2, Col3, Col4 FROM MyTable WHERE (@FieldToSearchBy e.g Col3, @OperatorToUserInSearach e.g LIKE, @ValueToSearch e.g John) I want to pass @FieldToSearchBy, @OperatorToUserInSearach, @ValueToSearch) as user specified parameters at runtime I want to do this with a TableAdpter like in this example http://www.codeproject.com/KB/database/TableAdapter.aspx

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• Pros and Cons of Different macro function / inline methods in C

  - by Robert S. Barnes

  According to the C FAQ, there are basically 3 practical methods for "inlining" code in C: #define MACRO(arg1, arg2) do { \ /* declarations */ \ stmt1; \ stmt2; \ /* ... */ \ } while(0) /* (no trailing ; ) */ or #define FUNC(arg1, arg2) (expr1, expr2, expr3) To clarify this one, the arguments are used in the expressions, and the comma operator returns the value of the last expression. or using the inline declaration which is supported as an extension to gcc and in the c99 standard. The do { ... } while (0) method is widely used in the Linux kernel, but I haven't encountered the other two methods very often if at all. I'm referring specifically to multi-statement "functions", not single statement ones like MAX or MIN. What are the pros and cons of each method, and why would you choose one over the other in various situations?

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• jQuery if checkbox is checked to toggle classes

  - by Lynx

  I am needed to change my jQuery code up. Instead of the label toggling the class and showing the icon I need it to where if the checkbox is checked to show to toggle those classes. I have tried prop and is but I couldn't get them to work properly. The reason for the change is I want to preload data into the form and if it's going to be checked those toggles need to reflect that change. http://jsfiddle.net/70fbLooL/2/ EDIT Seems to be confusion as to exactly what I am trying to do. The fiddle I provided works perfectly fine. The problem is if I want to call the form from server-side and pre-populate the form the checkbox toggles will not show that they are checked because it's based on the clicked function. I need it to be based on if the checkbox equal true or checked. That way if the value equals true from the server-side call it will toggle those classes and look like it's checked.

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• symfony sfValidatorSchemaCompare and dateformat output problem

  - by Gerbrand

  public function configure() { $this->widgetSchema['start_date'] = new sfWidgetFormInput(); $this->widgetSchema['end_date'] = new sfWidgetFormInput(); $this->validatorSchema->setPostValidator( new sfValidatorOr ( array( new sfValidatorAnd( array (new sfValidatorSchemaCompare('start_date', sfValidatorSchemaCompare::NOT_EQUAL, null), new sfValidatorSchemaCompare('end_date', sfValidatorSchemaCompare::EQUAL, null) )), new sfValidatorSchemaCompare('start_date', sfValidatorSchemaCompare::LESS_THAN_EQUAL, 'end_date', array('throw_global_error' => false), array('invalid' => 'The start date ("%left_field%") must be before the end date ("%right_field%")'))))); } I've got following input dates which I want to check if the end date isn't before the start date: Input: Start = 31/03/10 End= 07/03/10 Output: The start date (2010-03-31) must be before the end date (2010-03-07) Can you in some way change the date output? I need the error message to set the date format the same as the input. Also my input fields are set with the wrong date format when the error appears. Tried several things, but no luck at this moment. Didn't find a solution or information on symfony it self. I'm using symfony version 1.2.11

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