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  • Comparing objects and inheritance

    - by ereOn
    Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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  • Correct way to initialize dynamic Array in C++

    - by mef
    Hey guys, I'm currently working on a C++ project, where dynamic arrays often appear. I was wondering, what could be the correct way to initialize a dynamic array using the new-operator? A colleague of mine told me that it's a no-no to use new within the constructor, since a constructor is a construct that shouldn't be prone to errors or shouldn't fail at all, respectively. Now let's consider the following example: We have two classes, a more or less complex class State and a class StateContainer, which should be self-explained. class State { private: unsigned smth; public: State(); State( unsigned s ); }; class StateContainer { private: unsigned long nStates; State *states; public: StateContainer(); StateContainer( unsigned long n ); virtual ~StateContainer(); }; StateContainer::StateContainer() { nStates = SOME_DEFINE_N_STATES; states = new State[nStates]; if ( !states ) { // Error handling } } StateContainer::StateContainer( unsigned long n ) { nStates = n; try { states = new State[nStates] } catch ( std::bad_alloc &e ) { // Error handling } } StateContainer::~StateContainer() { if ( states ) { delete[] states; states = 0; } } Now actually, I have two questions: 1.) Is it ok, to call new within a constructor, or is it better to create an extra init()-Method for the State-Array and why? 2.) Whats the best way to check if new succeeded: if (!ptr) std::cerr << "new failed." or try { /*new*/ } catch (std::bad_alloc) { /*handling*/ } 3.) Ok its three questions ;o) Under the hood, new does some sort of ptr = (Struct *)malloc(N*sizeof(Struct)); And then call the constructor, right?

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  • [javascript] Can I overload an object with a function?

    - by user257493
    Lets say I have an object of functions/values. I'm interested in overloading based on calling behavior. For example, this block of code below demonstrates what I wish to do. var main_thing = { initalized: false, something: "Hallo, welt!", something_else: [123,456,789], load: { sub1 : function() { //Some stuff }, sub2 : function() { //Some stuff }, all : function() { this.load.sub1(); this.load.sub2(); } } init: function () { this.initalized=true; this.something="Hello, world!"; this.something_else = [0,0,0]; this.load(); //I want this to call this.load.all() instead. } } The issue to me is that main_thing.load is assigned to an object, and to call main_thing.load.all() would call the function inside of the object (the () operator). What can I do to set up my code so I could use main_thing.load as an access the object, and main_thing.load() to execute some code? Or at least, similar behavior. Basically, this would be similar to a default constructor in other languages where you don't need to call main_thing.constructor(). If this isn't possible, please explain with a bit of detail.

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  • Why don't languages include implication as a logical operator?

    - by Maciej Piechotka
    It might be a strange question, but why there is no implication as a logical operator in many languages (Java, C, C++, Python Haskell - although as last one have user defined operators its trivial to add it)? I find logical implication much clearer to write (particularly in asserts or assert-like expressions) then negation with or: encrypt(buf, key, mode, iv = null) { assert (mode != ECB --> iv != null); assert (mode == ECB || iv != null); assert (implies(mode != ECB, iv != null)); // User-defined function }

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  • JqGrid - AfterInsertRow, setCell. programmatically change the contet of the cell

    - by oirfc
    Hello there, I am new to JqGrid, so please bare with me. I am having some problems with styling the cells when I use a showlink formatter. In my configuration I set up the AfterInsertRow and it works fine if I just display simple text: afterInsertRow: function(rowid, aData) { if (aData.Security == `C`) { jQuery('#list').setCell(rowid, 'Doc_Number', '', { color: `red` }); } else { jQuery('#list').setCell(rowid, 'Doc_Number', '', { color: `green` }); } }, ... This code works just fine, but as soon as I add a formatter {'Doc_Number, ..., 'formatter: ’showlink’, formatoptions: {baseLinkUrl: ’url.aspx’} the above code doesn't work because a new element is added to the cell <a href='url.aspx'>cellValue</a> Is it possible to access programmatically the new child element using something like the code above and change the style? <a href='url.aspx' style='color: red;'>cellValue</a> etc. Thanks in advance, oirfc

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  • Conditionally add htmlAttributes to ASP.NET MVC Html.ActionLink

    - by macca1
    I'm wondering if it's possible to conditionally add a parameter in a call to a method. For example, I am rendering a bunch of links (six total) for navigation in my Site.Master: <%= Html.ActionLink("About", "About", "Pages") %> | <%= Html.ActionLink("Contact", "Contact", "Pages") %> <%-- etc, etc. --%> I'd like to include a CSS class of "selected" for the link if it's on that page. So in my controller I'm returning this: ViewData.Add("CurrentPage", "About"); return View(); And then in the view I have an htmlAttributes dictionary: <% Dictionary<string,object> htmlAttributes = new Dictionary<string,object>(); htmlAttributes.Add("class","selected");%> Now my only question is how do I include the htmlAttributes for the proper ActionLink. I could do it this way for each link: <% htmlAttributes.Clear(); if (ViewData["CurrentPage"] == "Contact") htmlAttributes.Add("class","selected");%> <%= Html.ActionLink("Contact", "Contact", "Pages", htmlAttributes) %> But that seems a little repetitive. Is there some way to do something like this psuedo code: <%= Html.ActionLink("Contact", "Contact", "Pages", if(ViewData["CurrentPage"] == "Contact") { htmlAttributes }) %> That's obviously not valid syntax, but is there a correct way to do that? I'm open to any totally different suggestions for rendering these links. I'd like to stay with something like ActionLink that takes advantage of using my routes though instead of hard coding the tag.

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  • JqGrid - AfterInsertRow, setCell. programmatically change the content of the cell

    - by oirfc
    Hello there, I am new to JqGrid, so please bare with me. I am having some problems with styling the cells when I use a showlink formatter. In my configuration I set up the AfterInsertRow and it works fine if I just display simple text: afterInsertRow: function(rowid, aData) { if (aData.Security == `C`) { jQuery('#list').setCell(rowid, 'Doc_Number', '', { color: `red` }); } else { jQuery('#list').setCell(rowid, 'Doc_Number', '', { color: `green` }); } }, ... This code works just fine, but as soon as I add a formatter {'Doc_Number, ..., 'formatter: ’showlink’, formatoptions: {baseLinkUrl: ’url.aspx’} the above code doesn't work because a new element is added to the cell <a href='url.aspx'>cellValue</a> Is it possible to access programmatically the new child element using something like the code above and change the style? <a href='url.aspx' style='color: red;'>cellValue</a> etc. Thanks in advance, oirfc

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  • Pass value of a field to Silverlight ConverterParameter

    - by eidylon
    Hi all, I'm writing my very first Silverlight app. I have a datagrid with a column that has two labels, for the labels, i am using an IValueConverter to conditionally format the data. The label's "Content" is set as such: Content="{Binding HomeScore, Converter={StaticResource fmtshs}}" and Content="{Binding AwayScore, Converter={StaticResource fmtshs}}" The Convert method of my IValueConverter is such: Public Function Convert( ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert Dim score As Long = value, other As Long = parameter Return If(score < 0, "", If(score - other > 5, (other + 5).ToString, score.ToString) ) End Function So what i want to do is in the converter for HomeScore, i want to pass AwayScore to the ConverterParameter, and for AwayScore i want to pass the HomeScore to the converter. In the converter for either score i need to be able to know the value of the other score for formatting purposes. But i cannot figure out the syntax for binding the ConverterParameter to another field. I've tried the following: Content="{Binding HomeScore, Converter={StaticResource fmtshs}, ConverterParameter=AwayScore}" Content="{Binding HomeScore, Converter={StaticResource fmtshs}, ConverterParameter={AwayScore}}" Content="{Binding HomeScore, Converter={StaticResource fmtshs}, ConverterParameter={Binding AwayScore}}" But none of those seem to work. How do i pass a field value to the ConverterParameter?

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  • SQL: Return "true" if list of records exists?

    - by User
    An alternative title might be: Check for existence of multiple rows? Using a combination of SQL and C# I want a method to return true if all products in a list exist in a table. If it can be done in all in SQL that would be preferable. I have written a method that returns whether a single productID exists using the following SQL: SELECT productID FROM Products WHERE ProductID = @productID If this returns a row, then the c# method returns true, false otherwise. Now I'm wondering if I have a list of product IDs (not a huge list mind you, normally under 20). How can I write a query that will return a row if all the product id's exist and no row if one or more product id's does not exist? (Maybe something involving "IN" like: SELECT * FROM Products WHERE ProductID IN (1, 10, 100))

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  • Resulting .exe from PyInstaller with wxPython crashing

    - by Helgi Hrafn Gunnarsson
    I'm trying to compile a very simple wxPython script into an executable by using PyInstaller on Windows Vista. The Python script is nothing but a Hello World in wxPython. I'm trying to get that up and running as a Windows executable before I add any of the features that the program needs to have. But I'm already stuck. I've jumped through some loops in regards to MSVCR90.DLL, MSVCP90.DLL and MSVCPM90.DLL, which I ended up copying from my Visual Studio installation (C:\Program Files\Microsoft Visual Studio 9.0\VC\redist\x86\Microsoft.VC90.CRT). As according to the instructions for PyInstaller, I run: Command: Configure.py Output: I: computing EXE_dependencies I: Finding TCL/TK... I: could not find TCL/TK I: testing for Zlib... I: ... Zlib available I: Testing for ability to set icons, version resources... I: ... resource update available I: Testing for Unicode support... I: ... Unicode available I: testing for UPX... I: ...UPX available I: computing PYZ dependencies... So far, so good. I continue. Command: Makespec.py -F guitest.py Output: wrote C:\Code\PromoUSB\guitest.spec now run Build.py to build the executable Then there's the final command. Command: Build.py guitest.spec Output: checking Analysis building Analysis because out0.toc non existent running Analysis out0.toc Analyzing: C:\Python26\pyinstaller-1.3\support\_mountzlib.py Analyzing: C:\Python26\pyinstaller-1.3\support\useUnicode.py Analyzing: guitest.py Warnings written to C:\Code\PromoUSB\warnguitest.txt checking PYZ rebuilding out1.toc because out1.pyz is missing building PYZ out1.toc checking PKG rebuilding out3.toc because out3.pkg is missing building PKG out3.pkg checking ELFEXE rebuilding out2.toc because guitest.exe missing building ELFEXE out2.toc I get the resulting 'guitest.exe' file, but upon execution, it "simply crashes"... and there is no debug info. It's just one of those standard Windows Vista crashes. The script itself, guitest.py runs just fine by itself. It only crashes as an executable, and I'm completely lost. I don't even know what to look for, since nothing I've tried has returned any relevant results. Another file is generated as a result of the compilation process, called 'warnguitest.txt'. Here are its contents. W: no module named posix (conditional import by os) W: no module named optik.__all__ (top-level import by optparse) W: no module named readline (delayed, conditional import by cmd) W: no module named readline (delayed import by pdb) W: no module named pwd (delayed, conditional import by posixpath) W: no module named org (top-level import by pickle) W: no module named posix (delayed, conditional import by iu) W: no module named fcntl (conditional import by subprocess) W: no module named org (top-level import by copy) W: no module named _emx_link (conditional import by os) W: no module named optik.__version__ (top-level import by optparse) W: no module named fcntl (top-level import by tempfile) W: __all__ is built strangely at line 0 - collections (C:\Python26\lib\collections.pyc) W: delayed exec statement detected at line 0 - collections (C:\Python26\lib\collections.pyc) W: delayed conditional __import__ hack detected at line 0 - doctest (C:\Python26\lib\doctest.pyc) W: delayed exec statement detected at line 0 - doctest (C:\Python26\lib\doctest.pyc) W: delayed conditional __import__ hack detected at line 0 - doctest (C:\Python26\lib\doctest.pyc) W: delayed __import__ hack detected at line 0 - encodings (C:\Python26\lib\encodings\__init__.pyc) W: __all__ is built strangely at line 0 - optparse (C:\Python26\pyinstaller-1.3\optparse.pyc) W: __all__ is built strangely at line 0 - dis (C:\Python26\lib\dis.pyc) W: delayed eval hack detected at line 0 - os (C:\Python26\lib\os.pyc) W: __all__ is built strangely at line 0 - __future__ (C:\Python26\lib\__future__.pyc) W: delayed conditional __import__ hack detected at line 0 - unittest (C:\Python26\lib\unittest.pyc) W: delayed conditional __import__ hack detected at line 0 - unittest (C:\Python26\lib\unittest.pyc) W: __all__ is built strangely at line 0 - tokenize (C:\Python26\lib\tokenize.pyc) W: __all__ is built strangely at line 0 - wx (C:\Python26\lib\site-packages\wx-2.8-msw-unicode\wx\__init__.pyc) W: __all__ is built strangely at line 0 - wx (C:\Python26\lib\site-packages\wx-2.8-msw-unicode\wx\__init__.pyc) W: delayed exec statement detected at line 0 - bdb (C:\Python26\lib\bdb.pyc) W: delayed eval hack detected at line 0 - bdb (C:\Python26\lib\bdb.pyc) W: delayed eval hack detected at line 0 - bdb (C:\Python26\lib\bdb.pyc) W: delayed __import__ hack detected at line 0 - pickle (C:\Python26\lib\pickle.pyc) W: delayed __import__ hack detected at line 0 - pickle (C:\Python26\lib\pickle.pyc) W: delayed conditional exec statement detected at line 0 - iu (C:\Python26\pyinstaller-1.3\iu.pyc) W: delayed conditional exec statement detected at line 0 - iu (C:\Python26\pyinstaller-1.3\iu.pyc) W: delayed eval hack detected at line 0 - gettext (C:\Python26\lib\gettext.pyc) W: delayed __import__ hack detected at line 0 - optik.option_parser (C:\Python26\pyinstaller-1.3\optik\option_parser.pyc) W: delayed conditional eval hack detected at line 0 - warnings (C:\Python26\lib\warnings.pyc) W: delayed conditional __import__ hack detected at line 0 - warnings (C:\Python26\lib\warnings.pyc) W: __all__ is built strangely at line 0 - optik (C:\Python26\pyinstaller-1.3\optik\__init__.pyc) W: delayed exec statement detected at line 0 - pdb (C:\Python26\lib\pdb.pyc) W: delayed conditional eval hack detected at line 0 - pdb (C:\Python26\lib\pdb.pyc) W: delayed eval hack detected at line 0 - pdb (C:\Python26\lib\pdb.pyc) W: delayed conditional eval hack detected at line 0 - pdb (C:\Python26\lib\pdb.pyc) W: delayed eval hack detected at line 0 - pdb (C:\Python26\lib\pdb.pyc) I don't know what the heck to make of any of that. Again, my searches have been fruitless.

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  • filling array gradually with data from user

    - by neville
    I'm trying to fill an array with words inputted by user. Each word must be one letter longer than previous and one letter shorter than next one. Their length is equal to table row index, counting from 2. Words will finally create a one sided pyramid, like : A AB ABC ABCD Scanner sc = new Scanner(System.in); System.out.println("Give the height of array: "); String[] words = new String[height]; for(int i=2; i<height+2; i++){ System.out.println("Give word with "+i+" letters."); words[i-2] = sc.next(); while( words[i-2].length()>i-2 || words[i-2].length()<words[i-3].length() ){ words[i-2] = sc.next(); } } Currently the while loop doesn't influence scanner at all :/

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  • condition in recursion - best practise

    - by mo
    hi there! what's the best practise to break a loop? my ideas were: Child Find(Parent parent, object criteria) { Child child = null; foreach(Child wannabe in parent.Childs) { if (wannabe.Match(criteria)) { child = wannabe; break; } else { child = Find(wannabe, criteria); } } return child; } or Child Find(Parent parent, object criteria) { Child child = null; var conditionator = from c parent.Childs where child != null select c; foreach(Child wannabe in conditionator) { if (wannabe.Match(criteria)) { child = wannabe; } else { child = Find(wannabe, criteria); } } return child; } or Child Find(Parent parent, object criteria) { Child child = null; var enumerator = parent.Childs.GetEnumerator(); while(child != null && enumerator.MoveNext()) { if (enumerator.Current.Match(criteria)) { child = wannabe; } else { child = Find(wannabe, criteria); } } return child; } what do u think, any better ideas? i'm looking for the niciest solution :D mo

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  • How to put a breakpoint at the end of a function in windbg, so that I dont need to edit it even if s

    - by shan23
    I need to log some data when some functions are hit, both at the start of execution and and the end of it. While i have no problem with putting breakpoints at the start of the functions(using bu [module]!functionname, I dont know how to put a breakpoint at the end of a function, SUCH THAT i dont need to edit the breakpoint everytime i add/delete somelines from the file/function. I'm sure its a very common scenario, just that I dont know how its done !! Can anyone elucidate ?

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  • Mysql CASE - WHEN - THEN - returning wrong data type (blob)

    - by Jack
    Hi there. Im creating customizable product attributes in a web store - each attribute can have different type of data, each data type is stored in a separate column using corresponding mysql datatype. I Have a query like: SELECT products.id AS id, products.sku AS sku, products.name AS name, products.url_key AS url_key, attributes.name AS attribute, CASE WHEN `attribute_types`.`type` = 'text' THEN product_attribute_values.value_text WHEN `attribute_types`.`type` = 'float' THEN product_attribute_values.value_float WHEN `attribute_types`.`type` = 'price' THEN product_attribute_values.value_float WHEN `attribute_types`.`type` = 'integer' THEN product_attribute_values.value_integer WHEN `attribute_types`.`type` = 'multiple' THEN product_attribute_values.value_text WHEN `attribute_types`.`type` = 'dropdown' THEN product_attribute_values.value_text WHEN `attribute_types`.`type` = 'date' THEN product_attribute_values.value_date WHEN `attribute_types`.`type` = 'textarea' THEN product_attribute_values.value_textarea END as value from (...) Now, the problem is that when attribute_types.type equals to ?some-type? i want it to return a value as it's stored in product_attribute_values table. Currently I get BLOb every time. Should I use type-casting or there's some behind-the-scene magic that I dont know about, OR maybe there's some better alternative ?

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  • SQL Stored Queries - use result of query as boolean based on existence of records

    - by Christian Mann
    Just getting into SQL stored queries right now... anyway, here's my database schema (simplified for YOUR convenience): member ------ id INT PK board ------ id INT PK officer ------ id INT PK If you're into OOP, Officer Inherits Board Inherits Member. In other words, if someone is listed on the officer table, s/he is listed on the board table and the member table. I want to find out the highest privilege level someone has. So far my SP looks like this: DELIMITER // CREATE PROCEDURE GetAuthLevel(IN targetID MEDIUMINT) BEGIN IF SELECT `id` FROM `member` WHERE `id` = targetID; THEN IF SELECT `id` FROM `board` WHERE `id` = targetID; THEN IF SELECT `id` FROM `officer` WHERE `id` = targetID; THEN RETURN 3; /*officer*/ ELSE RETURN 2; /*board member*/ ELSE RETURN 1; /*general member*/ ELSE RETURN 0; /*not a member*/ END // DELIMITER ; The exact text of the error is #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT id FROM member WHERE id = targetID; THEN IF SEL' at line 4 I suspect the issue is in the arguments for the IF blocks. What I want to do is return true if the result-set is at least one -- i.e. the id was found in the table. Do any of you guys see anything to do here, or should I reconsider my database design into this:? person ------ id INT PK level SMALLINT

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  • Java: minimum number of operations for conjunctive inequalities?

    - by HH
    I try to simplify conditionals in for (int t=0,size=fo.getPrintViewsPerFile().size();t<size&&t<countPerFile;t++){, more precisely: t<s&&t<c You need to compare two times, then calc the boolean value from them. Is there any simpler way to do it? If no, how can you prove it? I can simplify it to some extent, proof tree.

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  • Declarative authorization and the if_attribute not working...

    - by ro
    I've been having almost the same issues as Victor Martin (you can see the questions asked here). I've got declarative authorization working for just about everything that doesn't involve using conditionals. E.g. has_permission_on :users, :to => [:edit, :update, :destroy] do if_attribute :user => is { current_user } end Are there any common pitfalls with Declarative Authorization? I'm using authlogic and I'm suspicious the 'current_user' method in the application controller might be the source of the problem.

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  • Disabling normal link behaviour on click with an if statement in Jquery?

    - by Qwibble
    I've been banging my head with this all day, trying anything and everything I can think of to no gain. I'm no Jquery guru, so am hoping someone here can help me out. What I'm trying to do in pseudo code (concept) seems practical and easy to implement, but obviously not so =D What I have is a navigation sidebar, with sub menu's within some li's, and a link at the head of each li. When a top level link is clicked, I want the jquery to check if the link has a sibling ul. If it does, the link doesn't act like a link, but slides down the sibling sub nav. If there isn't one, the link should act normally. Here's where I'm at currently, what am I doing wrong? $('ul.navigation li a').not('ul.navigation li ul li a').click(function (){ if($(this).parent().contains('ul')){ $('ul.navigation li ul').slideUp(); $(this).siblings('ul').slideDown(); return false; } else{ alert('Link Clicked') // Maybe do some more stuff in here... } }); Any ideas?

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  • php URI troube with if statement,

    - by sea_1987
    I am running an if statement, that looks like this, if($this->uri->segment(1) !== 'search' || $this->uri->segment(1) !== 'employment') { //dome something } My problem is that first condition works, if the uri segment 1 equals search then the method do not run however if I on the page employment, and the first segment of the uri is employment then the condition still runs, why is this?

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  • Is there any way to set or code breakpoints conditionally?

    - by froadie
    I've been wondering this for a while - is there a way to code/program breakpoints...? Conditionally? For example, can I specify something like - "when this variable becomes this value, break and open the debugger"? (Would be quite useful, especially in long loops when you want to debug loop execution of a late loop value.) I suppose this may be IDE-specific since debugging is implemented differently in different IDEs... I'd be interested to know how to do this in any IDE, but specifically in Eclipse and Visual Studio.

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  • XPath select an attribute based on value

    - by Apeksha
    Using VB.Net, I have an XmlNode object, xNode. I need to select an attribute of this node if it has a particular value. e.g. xNode.SelectSingleNode(".[@attr1='1']") I would expect this statement to return the attribute "attr1", only if it has a value of "1". However, I get an error - Expression must evaluate to a node-set. When I tried this - xNode.SelectSingleNode("@attr1[@attr1='1']") It always returns Nothing, even if the attribute has a value of 1. I have tried a lot of different things, but no luck yet. Please help. Thanks.

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  • An INSERT conditioned on COUNT

    - by Anders Feder
    How can I construct a MySQL INSERT query that only executes if the number of rows satisfying some condition already in the table is less than 20, and fails otherwise? That is, if the table has 18 rows satisfying the condition, then the INSERT should proceed. If the table has 23 rows satisfying the condition, then the INSERT should fail. For atomicity, I need to express this in a single query, so two requests can not INSERT at the same time, each in the 'belief' that only 19 rows satisfy the condition. Thank you.

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  • Controlled execution of computationally expensive tasks

    - by Sergio
    Say you have an application where a user is typing some text and as she types you'd want to perform some expensive computations in the background (related to the text that is being typed). Although you would like to do lots of things, your main priority is that the system responsiveness stay at acceptable levels so the user doesn't notice such a heavy load. Is there a way (ideally platform/language independent) to control what algorithms should be executed in the background based on the system load and responsiveness?

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