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• Which are the RDBMS that minimize the server roundtrips? Which RDBMS are better (in this area) than

  - by user193655

  When the latency is high ("when pinging the server takes time") the server roundtrips make the difference. Now I don't want to focus on the roundtrips created in programming, but the roundtrips that occur "under the hood" in the DB engine, so the roundtrips that are 100% dependant on how the RDBMS is written itself. I have been told that FireBird has more roundtrips than MySQL. But this is the only information I know. I am currently supporting MS SQL but I'd like to change RDBMS (because I use Express Editions and in my scenario they are quite limiting from the performance point of view), so to make a wise choice I would like to include also this point into "my RDBMS comparison feature matrix" to understand which is the best RDBMS to choose as an alternative to MS SQL. So the bold sentence above would make me prefer MySQL to Firebird (for the roundtrips concept, not in general), but can anyone add informations? And MS SQL where is it located? Is someone able to "rank" the roundtrip performance of the main RDBMS, or at least: MS SQL, MySql, Postegresql, Firebird (I am not interested in Oracle since it is not free, and if I have to change I would change to a free RDBMS). Anyway MySql (as mentioned several times on stackoverflow) has a not clear future and a not 100% free license. So my final choice will probably dall on PostgreSQL or Firebird. Additional info: somehow you can answer my question by making a simple list like: MSSQL:3; MySQL:1; Firebird:2; Postgresql:2 (where 1 is good, 2 average, 3 bad). Of course if you can post some links where the roundtrips per RDBMSs are compared it would be great

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• SSIS - Skip Missing Files

  - by Greg

  I have a SSIS 2008 package that calls about 10 other SSIS packages (legacy issues, don't ask). Each of those child packages loads a specific file into a table. But sometimes one or more of these input files will be missing. How can I let a child package fail (because a file is missing) but let the rest of the parent package keep on running? I've tried increasing the maximum error count on the parent package, the tasks in the parent package that call each child, and in the child package itself. None of that seemed to make any difference. I still get this error when I run it with a file missing: SSIS Warning Code DTS_W_MAXIMUMERRORCOUNTREACHED. The Execution method succeeded, but the number of errors raised (2) reached the maximum allowed (1); resulting in failure. This occurs when the number of errors reaches the number specified in MaximumErrorCount. Change the MaximumErrorCount or fix the errors. Edit: failpackageonfailure and faulparentonfailure are already all set to false everywhere.

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• XForms relation of 'constraint' and 'required' properties

  - by Danny

  As a reference, the most similar question already asked is: http://stackoverflow.com/questions/8667849/making-xforms-enforce-the-constraint-and-type-model-item-properties-only-when-fi The difference is that I cannot use the relevant properties since I do want the field to be visible and accessible. I'm attempting to make a XForms form that has the following properties: It displays a text field named 'information'. (for the example) This field must not be required, since it may not be necessary to enter data. (Or this data will be entered at a later time.) However, if data is entered in this field, it must adhere to the specified constraint. I cannot mark the field as not relevant since this would hide the field and some data may need to be entered in it. The trouble now is that even though the field has no data in it, the constraint is still enforced (i.e. even though it is not marked as 'required'). I have taken a look at the XForms 1.1 specification, however it does not seem to describe how the properties 'required' and 'constraint' should interact. The only option I see, is to add a part to the constraint such that an empty value is allowed. e.g.: . = '' or <actual-constraint However, I don't like this. It feels like a workaround to add this to every such field. Is there any other way to express that non-required fields should not need to match the constraint for that field? (Am I missing something?)

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• Clarification of atomic memory access for different OSs

  - by murrekatt

  I'm currently porting a Windows C++ library to MacOS as a hobby project as a learning experience. I stumbled across some code using the Win Interlocked* functions and thus I've been trying to read up on the subject in general. Reading related questions here in SO, I understand there are different ways to do these operations depending on the OS. Interlocked* in Windows, OSAtomic* in MacOS and I also found that compilers have builtin (intrinsic) operations for this. After reading gcc builtin atomic memory access, I'm left wondering what is the difference between intrinsic and the OSAtomic* or Interlocked* ones? I mean, can I not choose between OSAtomic* or gcc builtin if I'm on MacOS when I use gcc? The same if I'd be on Windows using gcc. I also read that on Windows Interlocked* come as both inline and intrinsic versions. What to consider when choosing between intrinsic or inline? In general, are there multiple options on OSs what to use? Or is this again "it depends"? If so, what does it depend on? Thanks!

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• Why does Rails screw up timezones when I am editing a resource?

  - by DJTripleThreat

  Steps to produce this: prompt>rails test_app prompt>cd test_app prompt>script/generate scaffold date_test my_date:datetime prompt>rake db:migrate now edit your app/views/date_tests/edit.html.erb: <h1>Editing date_test</h1> <% form_for(@date_test) do |f| %> <%= f.error_messages %> <p> RIGHT!<br/> <%= text_field_tag @date_test, f.object.my_date %> </p> <p> WRONG!<br /> <%= f.text_field :my_date %> </p> <p> <%= f.submit 'Update' %> </p> <% end %> <%= link_to 'Show', @date_test %> | <%= link_to 'Back', date_tests_path %> now edit your config/environment.rb: #add this config.time_zone = 'Central Time (US & Canada)' This recreates the problem I am having in my actual app. The problem with my app is that I'm storing a date in a hidden field and rendering a "user friendly" version. Creating a resource works fine but as soon as I try to edit it the time changes (it adds the difference between my current time zone configuration and UTC). go to http://localhost:3000/date_tests/new and save the time then go to reedit it and you will have two different representations of the date/time one which will save incorrectly and the other that will.

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• Rate Limit Calls To Api Using Cache

  - by namtax

  Hi I am using coldfusion to call the last.fm api, using a cfc bundle sourced from here I am concerned about going over the request limit, which is 5 requests per originating IP address per second, averaged over a 5 minute period. The cfc bundle has a central component which calls all the other components, which are split up into sections like "artist", "track" etc...This central component "lastFmApi.cfc." is initiated in my application, and persisted for the lifespan of the application // Application.cfc example <cffunction name="onApplicationStart"> <cfset var apiKey = '[your api key here]' /> <cfset var apiSecret = '[your api secret here]' /> <cfset application.lastFm = CreateObject('component', 'org.FrankFusion.lastFm.lastFmApi').init(apiKey, apiSecret) /> </cffunction> Now if I want to call the api through a handler/controller, for example my artist handler...I can do this <cffunction name="artistPage" cache="5 mins"> <cfset qAlbums = application.lastFm.user.getArtist(url.artistName) /> </cffunction> I am a bit confused towards caching, but am caching each call to the api in this handler for 5 mins, but does this make any difference, because each time someone hits a new artist page wont this still count as a fresh hit against the api? Wondering how best to tackle this Thanks

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• Why can't decimal numbers be represented exactly in binary?

  - by Barry Brown

  There have been several questions posted to SO about floating-point representation. For example, the decimal number 0.1 doesn't have an exact binary representation, so it's dangerous to use the == operator to compare it to another floating-point number. I understand the principles behind floating-point representation. What I don't understand is why, from a mathematical perspective, are the numbers to the right of the decimal point any more "special" that the ones to the left? For example, the number 61.0 has an exact binary representation because the integral portion of any number is always exact. But the number 6.10 is not exact. All I did was move the decimal one place and suddenly I've gone from Exactopia to Inexactville. Mathematically, there should be no intrinsic difference between the two numbers -- they're just numbers. By contrast, if I move the decimal one place in the other direction to produce the number 610, I'm still in Exactopia. I can keep going in that direction (6100, 610000000, 610000000000000) and they're still exact, exact, exact. But as soon as the decimal crosses some threshold, the numbers are no longer exact. What's going on? Edit: to clarify, I want to stay away from discussion about industry-standard representations, such as IEEE, and stick with what I believe is the mathematically "pure" way. In base 10, the positional values are: ... 1000 100 10 1 1/10 1/100 ... In binary, they would be: ... 8 4 2 1 1/2 1/4 1/8 ... There are also no arbitrary limits placed on these numbers. The positions increase indefinitely to the left and to the right.

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• Do variable references (alias) incure runtime costs in c++?

  - by cheshirekow

  Maybe this is a compiler specific thing. If so, how about for gcc (g++)? If you use a variable reference/alias like this: int x = 5; int& y = x; y += 10; Does it actually require more cycles than if we didn't use the reference. int x = 5; x += 10; In other words, does the machine code change, or does the "alias" happen only at the compiler level? This may seem like a dumb question, but I am curious. Especially in the case where maybe it would be convenient to temporarily rename some member variables just so that the math code is a little easier to read. Sure, we're not exactly talking about a bottleneck here... but it's something that I'm doing and so I'm just wondering if there is any 'actual' difference... or if it's only cosmetic.

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• BasicDBObject or QueryBuilder and some newbie questions of Java and mongo

  - by Kevin Xu

  hi I'm a fresh newbie to mongodb Q1 using query=new BasicDBObject(); query.put("i", new BasicDBObject("$gt",13)); and query=new QueryBuilder().put("i").Greaterthan(13).get() is there any difference inside of the system? Q2 I've created a class class findkv extends BasicDBObject{ //is gt gte lt lte public findkv(String fieldname,String op,Object tvalue) { if (op=="") this.put(fieldname,tvalue); else this.put(fieldname, new BasicDBObject(op,tvalue)); } } shall I use it or shall I just use original function? Q3 I've used mongo shell for a few weeks, and was customed to it, and find writing in mongo shell faster and shorter, which side has more advantage, writing in mongo or in java? I shall dump them from mongo to mysql Q4 I've an if (statement==true) return else dowhat; seems can't be compiled I know I can write if (statement!=true) dowhat else return, but can I still write in first style? q5 my eclipse is Eclipse Java EE IDE for Web Developers. Version: Juno Release Build id: 20120614-1722 I'd like to install Perl which I haven't learned yet I choose Install Update http://e-p-i-c.sf.net/updates/testing but it doesn't work, any method to install perl to eclipse manually?

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• Help a CRUD programmer think about an "approval workflow"

  - by gerdemb

  I've been working on a web application that is basically a CRUD application (Create, Read, Update, Delete). Recently, I've started working on what I'm calling an "approval workflow". Basically, a request is generated for a material and then sent for approval to a manager. Depending on what is requested, different people need to approve the request or perhaps send it back to the requester for modification. The approvers need to keep track of what to approve what has been approved and the requesters need to see the status of their requests. As a "CRUD" developer, I'm having a hard-time wrapping my head around how to design this. What database tables should I have? How do I keep track of the state of the request? How should I notify users of actions that have happened to their requests? Is their a design pattern that could help me with this? Should I be drawing state-machines in my code? I think this is a generic programing question, but if it makes any difference I'm using Django with MySQL.

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• Diffrernce between BackgroundWorker.ReportProgress() and Control.Invoke()

  - by ohadsc

  What is the difference between options 1 and 2 in the following? private void BGW_DoWork(object sender, DoWorkEventArgs e) { for (int i=1; i<=100; i++) { string txt = i.ToString(); if (Test_Check.Checked) //OPTION 1 Test_BackgroundWorker.ReportProgress(i, txt); else //OPTION 2 this.Invoke((Action<int, string>)UpdateGUI, new object[] {i, txt}); } } private void BGW_ProgressChanged(object sender, ProgressChangedEventArgs e) { UpdateGUI(e.ProgressPercentage, (string)e.UserState); } private void UpdateGUI(int percent, string txt) { Test_ProgressBar.Value = percent; Test_RichTextBox.AppendText(txt + Environment.NewLine); } Looking at reflector, the Control.Invoke() appears to use: this.FindMarshalingControl().MarshaledInvoke(this, method, args, 1); whereas BackgroundWorker.Invoke() appears to use: this.asyncOperation.Post(this.progressReporter, args); (I'm just guessing these are the relevant function calls.) If I understand correctly, BGW Posts to the WinForms window its progress report request, whereas Control.Invoke uses a CLR mechanism to invoke on the right thread. Am I close? And if so, what are the repercussions of using either ? Thanks

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• What is different about C++ math.h abs() compared to my abs()

  - by moka

  I am currently writing some glsl like vector math classes in c++, and I just implemented an abs() function like this: template<class T> static inline T abs(T _a) { return _a < 0 ? -_a : _a; } I compared its speed to the default c++ abs from math.h like this: clock_t begin = clock(); for(int i=0; i<10000000; ++i) { float a = abs(-1.25); }; clock_t end = clock(); unsigned long time1 = (unsigned long)((float)(end-begin) / ((float)CLOCKS_PER_SEC/1000.0)); begin = clock(); for(int i=0; i<10000000; ++i) { float a = myMath::abs(-1.25); }; end = clock(); unsigned long time2 = (unsigned long)((float)(end-begin) / ((float)CLOCKS_PER_SEC/1000.0)); std::cout<<time1<<std::endl; std::cout<<time2<<std::endl; Now the default abs takes about 25ms while mine takes 60. I guess there is some low level optimisation going on. Does anybody know how math.h abs works internally? The performance difference is nothing dramatic, but I am just curious!

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• Wrapper Classes for Backward compatibility in Java

  - by Casebash

  There is an interesting article here on maintaing backwards compatibility for Java. In the wrapper class section, I can't actually understand what the wrapper class accomplishes. In the following code from MyApp, WrapNewClass.checkAvailable() could be replaced by Class.forName("NewClass"). static { try { WrapNewClass.checkAvailable(); mNewClassAvailable = true; } catch (Throwable ex) { mNewClassAvailable = false; } } Consider when NewClass is unavailable. In the code where we use the wrapper (see below), all we have done is replace a class that doesn't exist, with one that exists, but which can't be compiled as it uses a class that doesn't exist. public void diddle() { if (mNewClassAvailable) { WrapNewClass.setGlobalDiv(4); WrapNewClass wnc = new WrapNewClass(40); System.out.println("newer API is available - " + wnc.doStuff(10)); }else { System.out.println("newer API not available"); } } Can anyone explain why this makes a difference? I assume it has something to do with how Java compiles code - which I don't know much about.

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• pure/const functions in C++

  - by Albert

  Hi, I'm thinking of using pure/const functions more heavily in my C++ code. (pure/const attribute in GCC) However, I am curious how strict I should be about it and what could possibly break. The most obvious case are debug outputs (in whatever form, could be on cout, in some file or in some custom debug class). I probably will have a lot of functions, which don't have any side effects despite this sort of debug output. No matter if the debug output is made or not, this will absolutely have no effect on the rest of my application. Or another case I'm thinking of is the use of my own SmartPointer class. In debug mode, my SmartPointer class has some global register where it does some extra checks. If I use such an object in a pure/const function, it does have some slight side effects (in the sense that some memory probably will be different) which should not have any real side effects though (in the sense that the behaviour is in any way different). Similar also for mutexes and other stuff. I can think of many complex cases where it has some side effects (in the sense of that some memory will be different, maybe even some threads are created, some filesystem manipulation is made, etc) but has no computational difference (all those side effects could very well be left out and I would even prefer that). How does it work out in practice? If I mark such functions as pure/const, could it break anything (considering that the code is all correct)?

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• Fails proceeding after POSTing to web server

  - by OverTheRainbow

  Hello According to this question, it seems like the error "Too many automatic redirections were attempted" is caused when forgetting to use a cookiecontainer to connect to a web server that uses cookies to keep track of the user. However, even though I used "request.CookieContainer = MyCookieContainer", I'm still getting into an endless loop that is terminated by VB Express with this error message. Imports System.IO Imports System.Net 'Remember to add reference to System.Web DLL Imports System.Web Imports System.Text Public Class Form1 Const ConnectURL = "http://www.acme.com/logon.php" Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim request As HttpWebRequest = WebRequest.Create(ConnectURL) 'Build POST data request.Method = "POST" request.ContentType = "application/x-www-form-urlencoded" Dim Data As New StringBuilder Data.Append("Account=" + HttpUtility.UrlEncode("jdoe")) Data.Append("&Password=" + HttpUtility.UrlEncode("test")) Dim byteData() As Byte byteData = UTF8Encoding.UTF8.GetBytes(Data.ToString()) request.ContentLength = byteData.Length Dim postStream As Stream = Nothing Try postStream = request.GetRequestStream() postStream.Write(byteData, 0, byteData.Length) Finally If Not postStream Is Nothing Then postStream.Close() End Try 'Dim MyCookieContainer As New CookieContainer Dim MyCookieContainer As CookieContainer = New CookieContainer() request.CookieContainer = MyCookieContainer 'Makes no difference 'request.KeepAlive = True 'request.AllowAutoRedirect = True Dim response As HttpWebResponse 'HERE '"Too many automatic redirections were attempted" response = request.GetResponse() Dim reader As StreamReader = New StreamReader(response.GetResponseStream()) RichTextBox1.Text = reader.ReadToEnd End Sub End Class This is probably a newbie issue, but I don't know what else to try. Any idea? Thank you for any hint.

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• Emptying the datastore in GAE

  - by colwilson

  I know what you're thinking, 'O not that again!', but here we are since Google have not yet provided a simpler method. I have been using a queue based solution which worked fine: import datetime from models import * DELETABLE_MODELS = [Alpha, Beta, AlphaBeta] def initiate_purge(): for e in config.DELETABLE_MODELS: deferred.defer(delete_entities, e, 'purging', _queue = 'purging') class NotEmptyException(Exception): pass def delete_entities(e, queue): try: q = e.all(keys_only=True) db.delete(q.fetch(200)) ct = q.count(1) if ct > 0: raise NotEmptyException('there are still entities to be deleted') else: logging.info('processing %s completed' % queue) except Exception, err: deferred.defer(delete_entities, e, then, queue, _queue = queue) logging.info('processing %s deferred: %s' % (queue, err)) All this does is queue a request to delete some data (once for each class) and then if the queued process either fails or knows there is still some stuff to delete, it re-queues itself. This beats the heck out of hitting the refresh on a browser for 10 minutes. However, I'm having trouble deleting AlphaBeta entities, there are always a few left at the end. I think because it contains Reference Properties: class AlphaBeta(db.Model): alpha = db.ReferenceProperty(Alpha, required=True, collection_name='betas') beta = db.ReferenceProperty(Beta, required=True, collection_name='alphas') I have tried deleting the indexes relating to these entity types, but that did not make any difference. Any advice would be appreciated please.

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• C# / IronPython Interop with shared C# Class Library

  - by Adam Haile

  I'm trying to use IronPython as an intermediary between a C# GUI and some C# libraries, so that it can be scripted post compile time. I have a Class library DLL that is used by both the GUI and the python and is something along the lines of this: namespace MyLib { public class MyClass { public string Name { get; set; } public MyClass(string name) { this.Name = name; } } } The IronPython code is as follows: import clr clr.AddReferenceToFile(r"MyLib.dll") from MyLib import MyClass ReturnObject = MyClass("Test") Then, in C# I would call it as follows: ScriptEngine engine = Python.CreateEngine(); ScriptScope scope = null; scope = engine.CreateScope(); ScriptSource source = engine.CreateScriptSourceFromFile("Script.py"); source.Execute(scope); MyClass mc = scope.GetVariable<MyClass>("ReturnObject ") When I call this last bit of code, source.Execute(scope) runs returns successfully, but when I try the GetVariable call, it throw the following exception Microsoft.Scripting.ArgumentTypeException: expected MyClass , got MyClass So, you can see that the class names are exactly the same, but for some reason it thinks they are different. The DLL is in a different directory than the .py file (I just didn't bother to write out all the path setup stuff), could it be that there is an issue with the interpreter for IronPython seeing these objects as difference because it's somehow seeing them as being in a different context or scope?

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• Resque: Slow worker startup and Forking

  - by David John

  I'm currently moving my application from a Linode setup to EC2. Redis is currently installed on a remote instance with various worker instances interacting with the queue. Thats all going fantastic. My problem is with the amount of time it takes for a worker to be 'instantiated' and slow forking. Starting a worker will usually take between 30 seconds and a minute(from god.rb starting the worker rake task and the worker actively starting work on the queue). I could live with that, but I've not experienced such a wait time on my current Linode production box so I believe its one of my symptoms to a bigger problem. Next issue is that jobs that took a second or less in my previous environment now seem to take about 5 to 10 times longer.. I'm assuming this must be some sort of issue with my Ubuntu install on EC2? One notable difference is that I'm running REE 1.8.7-2010.01 in my new setup, and REE 1.8.6 on the old Linode boxes. Anyone else experienced these issues?

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• leak in fgets when assigning to buffer

  - by monkeyking

  I'm having problems understanding why following code leaks in one case, and not in the other case. The difference is while(NULL!=fgets(buffer,length,file))//doesnt leak while(NULL!=(buffer=fgets(buffer,length,file))//leaks I thought it would be the same. Full code below. #include <stdio.h> #include <stdlib.h> #define LENS 10000 void no_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=fgets(buffer,LENS,fp)){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); } void with_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=(buffer=fgets(buffer,LENS,fp))){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); }

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• I need help understanding how this jQuery filter function works, line-by-line, if possible

  - by user717236

  Here is the HTML: <div> <h3>text</h3> </div> <div> <h3>moretext</h3> </div> <div> <h3>123</h3> </div>?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? Here is the JS: var rv1_wlength = $("div").filter(function() { return $(this).find("h3").filter(function () { return $(this).text() != "123"; }).length; }); var rv1_wolength = $("div").filter(function() { return $(this).find("h3").filter(function () { return $(this).text() != "123"; }); }); var rv2 = $("div").find("h3").filter(function() { return $(this).text() != "123"; }); alert(rv1_wlength.text()); // text // moretext alert(rv1_wolength.text()); // text // moretext // 123 alert(rv2.text());? // textmoretext I don't understand why the first two methods print the elements on each line, whereas the second method concatenates them. "rv2" is a jQuery object. Then, what are the first two (rv1_wlength and rv1_wolength)? Furthermore, I don't understand why the inclusion of the length property makes all the difference in filtering the elements. The second method does nothing, since it returns all the elements. The first method, with the only change being the addition of the length property, correctly filters the elements. I would very much like a line-by-line explanation. I would sincerely appreciate any feedback. Thank you.

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• what use does the javascript forEach method have (that map can't do)?

  - by JohnMerlino

  Hey all, The only difference I see in map and foreach is that map is returning an array and foreach is not. However, I don't even understand the last line of the foreach method "func.call(scope, this[i], i, this);". For example, isn't "this" and "scope" referring to same object and isn't this[i] and i referring to the current value in the loop? I noticed on another post someone said "Use forEach when you want to do something on the basis of each element of the list. You might be adding things to the page, for example. Essentially, it's great for when you want "side effects". I don't know what is meant by side effects. Array.prototype.map = function(fnc) { var a = new Array(this.length); for (var i = 0; i < this.length; i++) { a[i] = fnc(this[i]); } return a; } Array.prototype.forEach = function(func, scope) { scope = scope || this; for (var i = 0, l = this.length; i < l; i++) func.call(scope, this[i], i, this); } Finally, are there any real uses for these methods in javascript (since we aren't updating a database) other than to manipulate numbers like this: alert([1,2,3,4].map(function(x){ return x + 1})); //this is the only example I ever see of map in javascript. Thanks for any reply.

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• Type classe, generic memoization

  - by nicolas

  Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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• Practice of checking 'trueness' or 'equality' in conditional statements - does it really make sense?

  - by Senthil

  I remember many years back, when I was in school, one of my computer science teachers taught us that it was better to check for 'trueness' or 'equality' of a condition and not the negative stuff like 'inequality'. Let me elaborate - If a piece of conditional code can be written by checking whether an expression is true or false, we should check the 'trueness'. Example: Finding out whether a number is odd - it can be done in two ways: if ( num % 2 != 0 ) { // Number is odd } or if ( num % 2 == 1 ) { // Number is odd } When I was beginning to code, I knew that num % 2 == 0 implies the number is even, so I just put a ! there to check if it is odd. But he was like 'Don't check NOT conditions. Have the practice of checking the 'trueness' or 'equality' of conditions whenever possible.' And he recommended that I use the second piece of code. I am not for or against either but I just wanted to know - what difference does it make? Please don't reply 'Technically the output will be the same' - we ALL know that. Is it a general programming practice or is it his own programming practice that he is preaching to others?

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• c# "==" operator : compiler behaviour with different structs

  - by Moe Sisko

  Code to illustrate : public struct MyStruct { public int SomeNumber; } public string DoSomethingWithMyStruct(MyStruct s) { if (s == null) return "this can't happen"; else return "ok"; } private string DoSomethingWithDateTime(DateTime s) { if (s == null) return "this can't happen"; // XX else return "ok"; } Now, "DoSomethingWithStruct" fails to compile with : "Operator '==' cannot be applied to operands of type 'MyStruct' and '<null>'". This makes sense, since it doesn't make sense to try a reference comparison with a struct, which is a value type. OTOH, "DoSomethingWithDateTime" compiles, but with compiler warning : "Unreachable code detected" at line marked "XX". Now, I'm assuming that there is no compiler error here, because the DateTime struct overloads the "==" operator. But how does the compiler know that the code is unreachable ? e.g. Does it look inside the code which overloads the "==" operator ? (This is using Visual Studio 2005 in case that makes a difference). Note : I'm more curious than anything about the above. I don't usually try to use "==" on structs and nulls.

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• Visual studio erroneous errors when building a website?

  - by Curtis White

  Visual Studio 2008 shows a lot of erroneous errors when building a website (not a web project) in the errors list. These errors are usually corrected (removed) when I rebuild the site a couple times but they cost me wasted time. Is there anyway to hide the erroneous errors? Update: I've decided to look into this to see if I could reproduce it. This is the exact behavior I am seeing, using the website model, I type some invalid syntax on a page. The errors list fills up with errors. I correct the error and the errors list does not update. I build the project and the errors list still shows the errors but the build shows as build completed. I build the project a second time and the errors list is cleared. My question is there anyway to make the errors list clear on the first build? I thought it might have something to do with page build vs website build but it seems to make no difference. I am not using any third party dlls on this website.

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