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• What are the pros and cons of using manual list iteration vs recursion through fail

  - by magus

  I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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• Finding contained bordered regions from Excel imports.

  - by dmaruca

  I am importing massive amounts of data from Excel that have various table layouts. I have good enough table detection routines and merge cell handling, but I am running into a problem when it comes to dealing with borders. Namely performance. The bordered regions in some of these files have meaning. Data Setup: I am importing directly from Office Open XML using VB6 and MSXML. The data is parsed from the XML into a dictionary of cell data. This wonks wonderfully and is just as fast as using docmd.transferspreadsheet in Access, but returns much better results. Each cell contains a pointer to a style element which contains a pointer to a border element that defines the visibility and weight of each border (this is how the data is structured inside OpenXML, also). Challenge: What I'm trying to do is find every region that is enclosed inside borders, and create a list of cells that are inside that region. What I have done: I initially created a BFS(breadth first search) fill routine to find these areas. This works wonderfully and fast for "normal" sized spreadsheets, but gets way too slow for imports into the thousands of rows. One problem is that a border in Excel could be stored in the cell you are checking or the opposing border in the adjacent cell. That's ok, I can consolidate that data on import to reduce the number of checks needed. One thing I thought about doing is to create a separate graph that outlines the cells using the borders as my edges and using a graph algorithm to find regions that way, but I'm having trouble figuring out how to implement the algorithm. I've used Dijkstra in the past and thought I could do similar with this. So I can span out using no endpoint to search the entire graph, and if I encounter a closed node I know that I just found an enclosed region, but how can I know if the route I've found is the optimal one? I guess I could flag that to run a separate check for the found closed node to the previous node ignoring that one edge. This could work, but wouldn't be much better performance wise on dense graphs. Can anyone else suggest a better method? Thanks for taking the time to read this.

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• WPF DataGrid, Help with Binding to a List<X> where each X has a Dictionary<Y,object> property.

  - by panamack

  I'm building an application which helps someone manage an event and works with data originating from Excel. I want to use the WPF Toolkit DataGrid to display the incoming data but can't guarantee how many Columns there are going to be or what information they will contain. I'd like to have an Info class that stores column information and have each Visitor at my Event own a Dictionary that uses shared references to Info objects for the keys. Here's the general gist: public class Info{ public string Name{get;set;} public int InfoType{get;set;} } public class Visitor{ public Dictionary<Info,object> VisitorInfo {get;set;} } public class Event{ public List<Visitor> Visitors{get;set;} public Event(){ Info i1 = new Info(){ Name = "ID", InfoType = 0};// type 0 for an id Info i2 = new Info(){ Name = "Name", InfoType = 1};// type 1 for a string Info i3 = new Info(){ Name = "City", InfoType = 1}; Visitor v1 = new Visitor(); v1.VisitorInfo.Add(i1, 0); v1.VisitorInfo.Add(i2, "Foo Harris"); v1.VisitorInfo.Add(i3, "Barsville"); Visitor v2 = new Visitor(); ... this.Visitors.Add(v1); this.Visitors.Add(v2); ... } } XAML: <!-- Window1.xaml --> ... <local:Event x:Key="MyEvent"/> ... <wpftk:DataGrid DataContext="{StaticResource MyEvent}" ItemsSource="{Binding Path=Visitors}" /> Disappointingly, DataGrid just sees a collection of Visitors each having a VisitorInfo property and displays one column called VisitorInfo with the string "(Collection)" once for each Visitor. As a workaround I've created a ListTVisitorToDataTableConverter that maps Infos to DataColumns and Visitors to DataRows and used it like this: <wpftk:DataGrid DataContext="{StaticResource Event}" ItemsSource{Binding Path=Visitors, Converter={StaticResource MySmellyListTVisitorToDataTableConverter}}" /> I don't think this is good though, I haven't started trying to convert back yet which I guess I'll need to do if I want to be able to edit any data! How can I do better? Thanks.

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• Sync services not actually syncing

  - by Paul Mrozowski

  I'm attempting to sync a SQL Server CE 3.5 database with a SQL Server 2008 database using MS Sync Services. I am using VS 2008. I created a Local Database Cache, connected it with SQL Server 2008 and picked the tables I wanted to sync. I selected SQL Server Tracking. It modified the database for change tracking and created a local copy (SDF) of the data. I need two way syncing so I created a partial class for the sync agent and added code into the OnInitialized() to set the SyncDirection for the tables to Bidirectional. I've walked through with the debugger and this code runs. Then I created another partial class for cache server sync provider and added an event handler into the OnInitialized() to hook into the ApplyChangeFailed event. This code also works OK - my code runs when there is a conflict. Finally, I manually made some changes to the server data to test syncing. I use this code to fire off a sync: var agent = new FSEMobileCacheSyncAgent(); var syncStats = agent.Synchronize(); syncStats seems to show the count of the # of changes I made on the server and shows that they were applied. However, when I open the local SDF file none of the changes are there. I basically followed the instructions I found here: http://msdn.microsoft.com/en-us/library/cc761546%28SQL.105%29.aspx and here: http://keithelder.net/blog/archive/2007/09/23/Sync-Services-for-SQL-Server-Compact-Edition-3.5-in-Visual.aspx It seems like this should "just work" at this point, but the changes made on the server aren't in the local SDF file. I guess I'm missing something but I'm just not seeing it right now. I thought this might be because I appeared to be using version 1 of Sync Services so I removed the references to Microsoft.Synchronization.* assemblies, installed the Sync framework 2.0 and added the new version of the assemblies to the project. That hasn't made any difference. Ideas? Edit: I wanted to enable tracing to see if I could track this down but the only way to do that is through a WinForms app since it requires entries in the app.config file (my original project was a class library). I created a WinForms project and recreated everything and suddenly everything is working. So apparently this requires a WinForm project for some reason? This isn't really how I planned on using this - I had hoped to kick off syncing through another non-.NET application and provide the UI there so the experience was a bit more seemless to the end user. If I can't do that, that's OK, but I'd really like to know if/how to make this work as a class library project instead.

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• Ping remote server and wait to get data

  - by infinity

  Hi I'm building my first application for android and I've reached a point where I can't find a solution even have no idea what to search for in Google. So the problem: I am pinging a remote server with GET request through the application passing some parameters like file_id. Then the server gives back confirmation if the file exists or error otherwise, both in plain text. The error string is $$$ERROR$$$. Actually the confirmation is JSON string that holds the path to the file. If the file doesn't exists on the server it generated the error message and start downloading the file and processing it which normally takes 10-30 seconds. What would be the best way to check if the file is ready for download? I have DownloadFile class that extends AsyncTask but before I reach the point to download the file I need the URL which is dependant on the previous request which is in the main class in the UI thread. Here is some code: public class MainActivity extends Activity { private String getInfo() { // Create a new HttpClient and Post Header HttpClient httpClient = new DefaultHttpClient(); HttpGet httpPost = new HttpGet(infoUrl); StringBuilder sb = null; String data; JSONObject jObject = null; try { HttpResponse response = httpClient.execute(httpPost); // This might be equal "$$$ERROR$$$" if no file exists sb = inputStreamToString(response.getEntity().getContent()); } catch(ClientProtocolException e) { // TODO Auto-generated catch block Log.v("Error: pushItem ClientProtocolException: ", e.toString()); } catch (IOException e) { // TODO Auto-generated catch block Log.v("Error: pushItem IOException: ", e.toString()); } // Clean the data to be complaint JSON format data = sb.toString().replace("info = ", ""); try { jObject = new JSONObject(data); data = jObject.getString("h"); fileTitle = jObject.getString("title"); } catch (JSONException e) { // TODO Auto-generated catch block e.printStackTrace(); } downloadUrl = String.format(downloadUrl, fileId, data); return downloadUrl; } } So my idea was to get the content and if equal to $$$ERROR$$$ go into loop until JSON data is passed but I guess there is better solution. Note: I don't have control over the server output so have to deal with what I have.

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• mysql: can't set max_allowed_package to anything grater than 16MB

  - by sas

  I'm not sure if this is the right place to post these kind of questions, if it's not so, please (politely) let me know... :-) I need to save files greater than 16MB on a mysql database from a php site... I've already changed the c:\xampp\mysql\bin\my.cnf and set max_allowed_packet to 16 MB, and everything worked fine then I set it to 32 MB but there´s no way I can handle a file bigger than 16 MB I get the following error: 'MySQL server has gone away' (the same error I had when max_allowed_packet was set to 1MB) there must be some other setting that doesn´t allow me to handle files bigger than 16MB maybe the php client, I guess, but I don't know where to edit it this is the code I'm running when file.txt is smaller than 16.776.192 bytes long, it works fine, but if file.txt has 16.777.216 bytes i get the aforementioned error oh, and the field download.content is a longblob... $file = 'file.txt'; $file_handle = fopen( $file, 'r' ); $content = fread( $file_handle, filesize( $file ) ); fclose( $file_handle ); db_execute( 'truncate table download', true ); $sql = "insert into download( code, title, name, description, original_name, mime_type, size, content, user_insert_id, date_insert, user_update_id, date_update ) values ( 'new file', 'new file', 'sas.jpg', 'new file', '$file', 'mime', " . filesize( $file ) . ", '" . addslashes( $content ) . "', 0, " . db_char_to_sql( now_char(), 'datetime' ) . ", 0, " . db_char_to_sql( now_char(), 'datetime' ) . " )"; db_execute( $sql, true ); (the db_execute funcion just opens the connections and executes the sql stuff) running on windows XP sp2 server version: 5.0.67-community PHP Version 4.4.9 mysql client API version: 3.23.49 using: ApacheFriends XAMPP (Basispaket) version 1.6.8 that comes with + Apache 2.2.9 + MySQL 5.0.67 (Community Server) + PHP 5.2.6 + PHP 4.4.9 + PEAR + phpMyAdmin 2.11.9.2 ... this is part of the content of c:\xampp\mysql\bin\my.cnf # The MySQL server [mysqld] port= 3306 socket= "C:/xampp/mysql/mysql.sock" basedir="C:/xampp/mysql" tmpdir="C:/xampp/tmp" datadir="C:/xampp/mysql/data" skip-locking key_buffer = 16M # max_allowed_packet = 1M max_allowed_packet = 32M table_cache = 128 sort_buffer_size = 512K net_buffer_length = 8K read_buffer_size = 256K read_rnd_buffer_size = 512K myisam_sort_buffer_size = 8M

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• Efficient algorithm to distribute work?

  - by Zwei Steinen

  It's a bit complicated to explain but here we go. We have problems like this (code is pseudo-code, and is only for illustrating the problem. Sorry it's in java. If you don't understand, I'd be glad to explain.). class Problem { final Set<Integer> allSectionIds = { 1,2,4,6,7,8,10 }; final Data data = //Some data } And a subproblem is: class SubProblem { final Set<Integer> targetedSectionIds; final Data data; SubProblem(Set<Integer> targetedSectionsIds, Data data){ this.targetedSectionIds = targetedSectionIds; this.data = data; } } Work will look like this, then. class Work implements Runnable { final Set<Section> subSections; final Data data; final Result result; Work(Set<Section> subSections, Data data) { this.sections = SubSections; this.data = data; } @Override public void run(){ for(Section section : subSections){ result.addUp(compute(data, section)); } } } Now we have instances of 'Worker', that have their own state sections I have. class Worker implements ExecutorService { final Map<Integer,Section> sectionsIHave; { sectionsIHave = {1:section1, 5:section5, 8:section8 }; } final ExecutorService executor = //some executor. @Override public void execute(SubProblem problem){ Set<Section> sectionsNeeded = fetchSections(problem.targetedSectionIds); super.execute(new Work(sectionsNeeded, problem.data); } } phew. So, we have a lot of Problems and Workers are constantly asking for more SubProblems. My task is to break up Problems into SubProblem and give it to them. The difficulty is however, that I have to later collect all the results for the SubProblems and merge (reduce) them into a Result for the whole Problem. This is however, costly, so I want to give the workers "chunks" that are as big as possible (has as many targetedSections as possible). It doesn't have to be perfect (mathematically as efficient as possible or something). I mean, I guess that it is impossible to have a perfect solution, because you can't predict how long each computation will take, etc.. But is there a good heuristic solution for this? Or maybe some resources I can read up before I go into designing? Any advice is highly appreciated!

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• Basic data alignment question

  - by Broken Logic

  I've been playing around to see how my computer works under the hood. What I'm interested in is seeing is what happens on the stack inside a function. To do this I've written the following toy program: #include <stdio.h> void __cdecl Test1(char a, unsigned long long b, char c) { char c1; unsigned long long b1; char a1; c1 = 'b'; b1 = 4; a1 = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&b1 - (long)&a1, (long)&c1 - (long)&b1, (long)&a - (long)&c1, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&a1 ); }; struct TestStruct { char a; unsigned long long b; char c; }; void __cdecl Test2(char a, unsigned long long b, char c) { TestStruct locals; locals.a = 'b'; locals.b = 4; locals.c = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&locals.b - (long)&locals.a, (long)&locals.c - (long)&locals.b, (long)&a - (long)&locals.c, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&locals.a ); }; int main() { Test1('f', 0, 'o'); Test2('f', 0, 'o'); return 0; } And this spits out the following: 9 19 - 13 - 4 8 Total: 53 8 8 - 24 - 4 8 Total: 52 The function args are well behaved but as the calling convention is specified, I'd expect this. But the local variables are a bit wonky. My question is, why wouldn't these be the same? The second call seems to produce a more compact and better aligned stack. Looking at the ASM is unenlightening (at least to me), as the variable addresses are still aliased there. So I guess this is really a question about the assembler itself allocates the stack to local variables. I realise that any specific answer is likely to be platform specific. I'm more interested in a general explanation unless this quirk really is platform specific. For the record though, I'm compiling with VS2010 on a 64bit Intel machine.

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• Layout issue regarding a JQuery smoothDivScroll

  - by MichaelMcCabe

  Hi all. I have been scratching my head for a while on this one. I dont really play around with HTML formatting that often. I have a smoothDivScroll using JQuery (http://maaki.com/thomas/SmoothDivScroll/) to scroll through dynamically generated images. What I want it for, is to have multiple small images lined up right next to each other, and each image has a section of writting underneath. about 25 images, 140px width each in a 7560px span. I acheived this great by putting a table inside the div, and each image inside a<td>.This works problem i have, is that i need the slider to start from the furthest RIGHT image, and slide automatically left. This is acheived by (if you look at the link above) - startAtElementId: But if I am using a table inside the div, it is taking the TABLE as a element and not the TD... so it doesnt work. I know this because if I change every image to be inside tables (i.e 25 tables), it works... but obviously then the formatting is not how I want. Can anyone think of a way I can use this slider (modifications to the js code or not), with 25 images that NEED to be right next to each other, no gap. I guess this is more of a formatting question, than about the slider. Because I only know ONE way of doing what I want, and thats to have below which will not alow me to set startAtElementId. <div class="scrollableArea"> <table width="7560px" class="index-body"> <tr> <td width="140px"><center><a onclick="__doPostBack('getEarlierDate');" ><img src="../images/olderGraphs.gif" width="140" height="60"></a>Click for more</center></td> <td width="300px"><center><a onclick="__doPostBack('chartClicked25');" ><cewolf:img chartid="verticalbar25" renderer="cewolf" width="300" height="60"/></a><c:out value="${date25}"/></center></td> <td width="300px"><center><a onclick="__doPostBack('chartClicked24');" ><cewolf:img chartid="verticalbar24" renderer="cewolf" width="300" height="60"/></a><c:out value="${date24}"/></center></td> and so on

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• How to design service that can provide interface as JAX-WS web service, or via JMS, or as local meth

  - by kevinegham

  Using a typical JEE framework, how do I develop and deploy a service that can be called as a web service (with a WSDL interface), be invoked via JMS messages, or called directly from another service in the same container? Here's some more context: Currently I am responsible for a service (let's call it Service X) with the following properties: Interface definition is a human readable document kept up-to-date manually. Accepts HTTP form-encoded requests to a single URL. Sends plain old XML responses (no schema). Uses Apache to accept requests + a proprietary application server (not servlet or EJB based) containing all logic which runs in a seperate tier. Makes heavy use of a relational database. Called both by internal applications written in a variety of languages and also by a small number of third-parties. I want to (or at least, have been told to!): Switch to a well-known (pref. open source) JEE stack such as JBoss, Glassfish, etc. Split Service X into Service A and Service B so that we can take Service B down for maintenance without affecting Service A. Note that Service B will depend on (i.e. need to make requests to) Service A. Make both services easier for third parties to integrate with by providing at least a WS-I style interface (WSDL + SOAP + XML + HTTP) and probably a JMS interface too. In future we might consider a more lightweight API too (REST + JSON? Google Protocol Buffers?) but that's a nice to have. Additional consideration are: On a smaller deployment, Service A and Service B will likely to running on the same machine and it would seem rather silly for them to use HTTP or a message bus to communicate; better if they could run in the same container and make method calls to each other. Backwards compatibility with the existing ad-hoc Service X interface is not required, and we're not planning on re-using too much of the existing code for the new services. I'm happy with either contract-first (WSDL I guess) or (annotated) code-first development. Apologies if my terminology is a bit hazy - I'm pretty experienced with Java and web programming in general, but am finding it quite hard to get up to speed with all this enterprise / SOA stuff - it seems I have a lot to learn! I'm also not very used to using a framework rather than simply writing code that calls some packages to do things. I've got as far as downloading Glassfish, knocking up a simple WSDL file and using wsimport + a little dummy code to turn that into a WAR file which I've deployed.

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• Unit Testing - Am I doing it right?

  - by baron

  Hi everyone, Basically I have been programing for a little while and after finishing my last project can fully understand how much easier it would have been if I'd have done TDD. I guess I'm still not doing it strictly as I am still writing code then writing a test for it, I don't quite get how the test becomes before the code if you don't know what structures and how your storing data etc... but anyway... Kind of hard to explain but basically lets say for example I have a Fruit objects with properties like id, color and cost. (All stored in textfile ignore completely any database logic etc) FruitID FruitName FruitColor FruitCost 1 Apple Red 1.2 2 Apple Green 1.4 3 Apple HalfHalf 1.5 This is all just for example. But lets say I have this is a collection of Fruit (it's a List<Fruit>) objects in this structure. And my logic will say to reorder the fruitids in the collection if a fruit is deleted (this is just how the solution needs to be). E.g. if 1 is deleted, object 2 takes fruit id 1, object 3 takes fruit id2. Now I want to test the code ive written which does the reordering, etc. How can I set this up to do the test? Here is where I've got so far. Basically I have fruitManager class with all the methods, like deletefruit, etc. It has the list usually but Ive changed hte method to test it so that it accepts a list, and the info on the fruit to delete, then returns the list. Unit-testing wise: Am I basically doing this the right way, or have I got the wrong idea? and then I test deleting different valued objects / datasets to ensure method is working properly. [Test] public void DeleteFruit() { var fruitList = CreateFruitList(); var fm = new FruitManager(); var resultList = fm.DeleteFruitTest("Apple", 2, fruitList); //Assert that fruitobject with x properties is not in list ? how } private static List<Fruit> CreateFruitList() { //Build test data var f01 = new Fruit {Name = "Apple",Id = 1, etc...}; var f02 = new Fruit {Name = "Apple",Id = 2, etc...}; var f03 = new Fruit {Name = "Apple",Id = 3, etc...}; var fruitList = new List<Fruit> {f01, f02, f03}; return fruitList; }

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• I'm searching for a messaging platform (like XMPP) that allows tight integration with a web applicat

  - by loxs

  Hi, At the company I work for, we are building a cluster of web applications for collaboration. Things like accounting, billing, CRM etc. We are using a RESTfull technique: For database we use CouchDB Different applications communicate with one another and with the database via http. Besides, we have a single sign on solution, so that when you login in one application, you are automatically logged to the other. For all apps we use Python (Pylons). Now we need to add instant messaging to the stack. We need to support both web and desktop clients. But just being able to chat is not enough. We need to be able to achieve all of the following (and more similar things). When somebody gets assigned to a task, they must receive a message. I guess this is possible with some system daemon. There must be an option to automatically group people in groups by lots of different properties. For example, there must be groups divided both by geographical location, by company division, by job type (all the programers from different cities and different company divisions must form a group), so that one can send mass messages to a group of choice. Rooms should be automatically created and destroyed. For example when several people visit the same invoice, a room for them must be automatically created (and they must auto-join). And when all leave the invoice, the room must be destroyed. Authentication and authorization from our applications. I can implement this using custom solutions like hookbox http://hookbox.org/docs/intro.html but then I'll have lots of problems in supporting desktop clients. I have no former experience with instant messaging. I've been reading about this lately. I've been looking mostly at things like ejabberd. But it has been a hard time and I can't find whether what I want is possible at all. So I'd be happy if people with experience in this field could help me with some advice, articles, tales of what is possible etc.

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• Loading datasets from datastore and merge into single dictionary. Resource problem.

  - by fredrik

  Hi, I have a productdatabase that contains products, parts and labels for each part based on langcodes. The problem I'm having and haven't got around is a huge amount of resource used to get the different datasets and merging them into a dict to suit my needs. The products in the database are based on a number of parts that is of a certain type (ie. color, size). And each part has a label for each language. I created 4 different models for this. Products, ProductParts, ProductPartTypes and ProductPartLabels. I've narrowed it down to about 10 lines of code that seams to generate the problem. As of currently I have 3 Products, 3 Types, 3 parts for each type, and 2 languages. And the request takes a wooping 5500ms to generate. for product in productData: productDict = {} typeDict = {} productDict['productName'] = product.name cache_key = 'productparts_%s' % (slugify(product.key())) partData = memcache.get(cache_key) if not partData: for type in typeData: typeDict[type.typeId] = { 'default' : '', 'optional' : [] } ## Start of problem lines ## for defaultPart in product.defaultPartsData: for label in labelsForLangCode: if label.key() in defaultPart.partLabelList: typeDict[defaultPart.type.typeId]['default'] = label.partLangLabel for optionalPart in product.optionalPartsData: for label in labelsForLangCode: if label.key() in optionalPart.partLabelList: typeDict[optionalPart.type.typeId]['optional'].append(label.partLangLabel) ## end problem lines ## memcache.add(cache_key, typeDict, 500) partData = memcache.get(cache_key) productDict['parts'] = partData productList.append(productDict) I guess the problem lies in the number of for loops is too many and have to iterate over the same data over and over again. labelForLangCode get all labels from ProductPartLabels that match the current langCode. All parts for a product is stored in a db.ListProperty(db.key). The same goes for all labels for a part. The reason I need the some what complex dict is that I want to display all data for a product with it's default parts and show a selector for the optional one. The defaultPartsData and optionaPartsData are properties in the Product Model that looks like this: @property def defaultPartsData(self): return ProductParts.gql('WHERE __key__ IN :key', key = self.defaultParts) @property def optionalPartsData(self): return ProductParts.gql('WHERE __key__ IN :key', key = self.optionalParts) When the completed dict is in the memcache it works smoothly, but isn't the memcache reset if the application goes in to hibernation? Also I would like to show the page for first time user(memcache empty) with out the enormous delay. Also as I said above, this is only a small amount of parts/product. What will the result be when it's 30 products with 100 parts. Is one solution to create a scheduled task to cache it in the memcache every hour? It this efficient? I know this is alot to take in, but I'm stuck. I've been at this for about 12 hours straight. And can't figure out a solution. ..fredrik

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• Which is the "best" data access framework/approach for C# and .NET?

  - by Frans

  (EDIT: I made it a community wiki as it is more suited to a collaborative format.) There are a plethora of ways to access SQL Server and other databases from .NET. All have their pros and cons and it will never be a simple question of which is "best" - the answer will always be "it depends". However, I am looking for a comparison at a high level of the different approaches and frameworks in the context of different levels of systems. For example, I would imagine that for a quick-and-dirty Web 2.0 application the answer would be very different from an in-house Enterprise-level CRUD application. I am aware that there are numerous questions on Stack Overflow dealing with subsets of this question, but I think it would be useful to try to build a summary comparison. I will endeavour to update the question with corrections and clarifications as we go. So far, this is my understanding at a high level - but I am sure it is wrong... I am primarily focusing on the Microsoft approaches to keep this focused. ADO.NET Entity Framework Database agnostic Good because it allows swapping backends in and out Bad because it can hit performance and database vendors are not too happy about it Seems to be MS's preferred route for the future Complicated to learn (though, see 267357) It is accessed through LINQ to Entities so provides ORM, thus allowing abstraction in your code LINQ to SQL Uncertain future (see Is LINQ to SQL truly dead?) Easy to learn (?) Only works with MS SQL Server See also Pros and cons of LINQ "Standard" ADO.NET No ORM No abstraction so you are back to "roll your own" and play with dynamically generated SQL Direct access, allows potentially better performance This ties in to the age-old debate of whether to focus on objects or relational data, to which the answer of course is "it depends on where the bulk of the work is" and since that is an unanswerable question hopefully we don't have to go in to that too much. IMHO, if your application is primarily manipulating large amounts of data, it does not make sense to abstract it too much into objects in the front-end code, you are better off using stored procedures and dynamic SQL to do as much of the work as possible on the back-end. Whereas, if you primarily have user interaction which causes database interaction at the level of tens or hundreds of rows then ORM makes complete sense. So, I guess my argument for good old-fashioned ADO.NET would be in the case where you manipulate and modify large datasets, in which case you will benefit from the direct access to the backend. Another case, of course, is where you have to access a legacy database that is already guarded by stored procedures. ASP.NET Data Source Controls Are these something altogether different or just a layer over standard ADO.NET? - Would you really use these if you had a DAL or if you implemented LINQ or Entities? NHibernate Seems to be a very powerful and powerful ORM? Open source Some other relevant links; NHibernate or LINQ to SQL Entity Framework vs LINQ to SQL

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• Look over my C# SQLite Query, what am I doing wrong?

  - by CODe

  I'm writing a WinForms database application using SQLite and C#. I have a sqlite query that is failing, and I'm unsure as to where I'm going wrong, as I've tried everything I could think of. public DataTable searchSubs(String businessName, String contactName) { string SQL = null; if ((businessName != null && businessName != "") && (contactName != null && contactName != "")) { // provided business name and contact name for search SQL = "SELECT * FROM SUBCONTRACTOR WHERE BusinessName LIKE %@BusinessName% AND Contact LIKE %@ContactName%"; } else if ((businessName != null && businessName != "") && (contactName == null || contactName == "")) { // provided business name only for search SQL = "SELECT * FROM SUBCONTRACTOR WHERE BusinessName LIKE %@BusinessName%"; } else if ((businessName == null || businessName == "") && (contactName != null && contactName != "")) { // provided contact name only for search SQL = "SELECT * FROM SUBCONTRACTOR WHERE Contact LIKE %@ContactName%"; } else if ((businessName == null || businessName == "") && (contactName == null || contactName == "")) { // provided no search information SQL = "SELECT * FROM SUBCONTRACTOR"; } SQLiteCommand cmd = new SQLiteCommand(SQL); cmd.Parameters.AddWithValue("@BusinessName", businessName); cmd.Parameters.AddWithValue("@ContactName", contactName); cmd.Connection = connection; SQLiteDataAdapter da = new SQLiteDataAdapter(cmd); DataSet ds = new DataSet(); try { da.Fill(ds); DataTable dt = ds.Tables[0]; return dt; } catch (Exception e) { MessageBox.Show(e.ToString()); return null; } finally { cmd.Dispose(); connection.Close(); } } I continually get an error saying that it is failing near the %'s. That's all fine and dandy, but I guess I'm structuring it wrong, but I don't know where! I tried adding apostrophes around the "like" variables, like this: SQL = "SELECT * FROM SUBCONTRACTOR WHERE Contact LIKE '%@ContactName%'"; and quite honestly, that is all I can think of. Anyone have any ideas?

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• making a password-only auth with bcrypt and mongoose

  - by user3081123

  I want to create service that let you login only with password. You type a password and if this password exists - you are logged in and if it's not - username is generated and password is encrypted. I'm having some misunderstandings and hope someone would help me to show where I'm mistaken. I guess, it would look somewhat like this in agularjs First we receive a password in login controller. $scope.signup = function() { var user = { password: $scope.password, }; $http.post('/auth/signup', user); }; Send it via http.post and get in in our node server file. We are provided with a compare password bcrypt function userSchema.methods.comparePassword = function(candidatePassword, cb) { bcrypt.compare(candidatePassword, this.password, function(err, isMatch) { if (err) return cb(err); cb(null, isMatch); }); }; So right now we are creating function to catch our http request app.post('/auth/signup', function(req, res, next) { Inside we use a compair password function to realize if such password exists or not yet. So we have to encrypt a password with bcrypt to make a comparison First we hash it same way as in .pre var encPass; bcrypt.genSalt(10, function(err, salt) { if (err) return next(err); bcrypt.hash(req.body.password, salt, function(err, hash) { if (err) return next(err); encPass=hash; )}; )}; We have encrypted password stored in encPass so now we follow to finding a user in database with this password User.findOne({ password: encPass }, function(err, user) { if (user) { //user exists, it means we should pass an ID of this user to a controller to display it in a view. I don't know how. res.send({user.name}) //like this? How should controller receive this? With $http.post? } else { and now if user doesn't exist - we should create it with user ID generated by my function var nUser = new User({ name: generId(), password: req.body.password }); nUser.save(function(err) { if (err) return next(err); )}; )}; )}; Am I doing anything right? I'm pretty new to js and angular. If so - how do I throw a username back at controller? If someone is interested - this service exists for 100+ symbol passphrases so possibility of entering same passphrase as someone else is miserable. And yeah, If someone logged in under 123 password - the other guy will log in as same user if he entered 123 password, but hey, you are warned to make a big passphrase. So I'm confident about the idea and I only need a help with understanding and realization.

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• Parsing CSV: how can NSScanner recognize empty field (i.e. ,,)?

  - by Fabrizio Prosperi

  I am very new to Xcode and trying - as millions - to parse a CSV file. I have read many contributions and I am managing it but I have a problem when my NSScanner intercepts an empty field: "Field_A, Field_B,, Field_D". I guess it is because it ignores empty space by default, or in this case no space at all. String is: "Personal","2011-01-01","Personal","Cigarettes",,4.60,"Cash","", I tried to debug it using scanLocation: 2011-04-22 15:57:32.414 Spending[42015:a0f] Before while...scan location is:0 2011-04-22 15:57:32.414 Spending[42015:a0f] Account: "Personal" - scan location is:10 2011-04-22 15:57:32.415 Spending[42015:a0f] Date: "2011-01-01" - scan location is:23 2011-04-22 15:57:32.415 Spending[42015:a0f] Category: "Personal" - scan location is:34 2011-04-22 15:57:32.416 Spending[42015:a0f] Subcategory: "Cigarettes" - scan location is:47 2011-04-22 15:57:32.416 Spending[42015:a0f] Income: 4.600000 - scan location is:53 2011-04-22 15:57:32.416 Spending[42015:a0f] Expense: 0.000000 - scan location is:53 2011-04-22 15:57:32.417 Spending[42015:a0f] Payment: "Cash" - scan location is:60 2011-04-22 15:57:32.417 Spending[42015:a0f] Note: "" - scan location is:63 And as you can see after that even expense field gets no value (should be 4.60). Here is the relevant piece of code: NSScanner *scanner = [NSScanner scannerWithString:fileString]; [scanner setCharactersToBeSkipped: [NSCharacterSet characterSetWithCharactersInString:@"\n, "]]; NSString *account, *date, *category, *subcategory, *payment, *note; float income, expense; // Set up data delimiter using comma NSCharacterSet *commaSet; commaSet = [NSCharacterSet characterSetWithCharactersInString:@","]; NSLog (@"Before while...scan location is:%d\n", scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&account]; NSLog(@"Account: %@ - scan location is:%d\n",account, scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&date]; NSLog(@"Date: %@ - scan location is:%d\n",date, scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&category]; NSLog(@"Category: %@ - scan location is:%d\n",category, scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&subcategory]; NSLog(@"Subcategory: %@ - scan location is:%d\n",subcategory, scanner.scanLocation); [scanner scanFloat:&income]; NSLog(@"Income: %f - scan location is:%d\n",income, scanner.scanLocation); [scanner scanFloat:&expense]; NSLog(@"Expense: %f - scan location is:%d\n",expense, scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&payment]; NSLog(@"Payment: %@ - scan location is:%d\n",payment, scanner.scanLocation); [scanner scanUpToCharactersFromSet:commaSet intoString:&note]; NSLog(@"Note: %@\n - scan location is:%d",note, scanner.scanLocation); I tried looking carefully through NSScanner Class Reference, but could not get an idea? Do you have any? Thanks, Fabrizio.

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• Multiple Timers with setTimeInterval

  - by visibleinvisibly

  I am facing a problem with setInterval being used in a loop. I have a function subscribeFeed( ) which takes an array of urls as input. It loops through the url array and subscribes each url to getFeedAutomatically() using a setInterval function. so if three URL's are there in the array, then 3 setInterval's will be called. The problem is 1)how to distinguish which setInterval is called for which URL. 2)it is causing Runtime exception in setInterval( i guess because of closure problem in javascript) //constructor function myfeed(){ this.feedArray = []; } myfeed.prototype.constructor= myfeed; myfeed.prototype.subscribeFeed =function(feedUrl){ var i=0; var url; var count = 0; var _this = this; var feedInfo = { url : [], status : "" }; var urlinfo = []; feedUrl = (feedUrl instanceof Array) ? feedUrl : [feedUrl]; //notifyInterval = (notifyInterval instanceof Array) ? notifyInterval: [notifyInterval]; for (i = 0; i < feedUrl.length; i++) { urlinfo[i] = { url:'', notifyInterval:5000,// Default Notify/Refresh interval for the feed isenable:true, // true allows the feed to be fetched from the URL timerID: null, //default ID is null called : false, position : 0, getFeedAutomatically : function(url){ _this.getFeedUpdate(url); }, }; urlinfo[i].url = feedUrl[i].URL; //overide the default notify interval if(feedUrl[i].NotifyInterval /*&& (feedUrl[i] !=undefined)*/){ urlinfo[i].notifyInterval = feedUrl[i].NotifyInterval; } // Trigger the Feed registered event with the info about URL and status feedInfo.url[i] = feedUrl[i].URL; //Set the interval to get the feed. urlinfo[i].timerID = setInterval(function(){ urlinfo[i].getFeedAutomatically(urlinfo[i].url); }, urlinfo[i].notifyInterval); this.feedArray.push(urlinfo[i]); } } // The getFeedUpate function will make an Ajax request and coninue myfeed.prototype.getFeedUpdate = function( ){ } I am posting the same on jsfiddle http://jsfiddle.net/visibleinvisibly/S37Rj/ Thanking you in advance

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• representing an XML config file with an IXmlSerializable class

  - by Sarah Vessels

  I'm writing in C# and trying to represent an XML config file through an IXmlSerializable class. I'm unsure how to represent the nested elements in my config file, though, such as logLevel: <?xml version="1.0" encoding="utf-8" ?> <configuration> <logging> <logLevel>Error</logLevel> </logging> <credentials> <user>user123</user> <host>localhost</host> <password>pass123</password> </credentials> <credentials> <user>user456</user> <host>my.other.domain.com</host> <password>pass456</password> </credentials> </configuration> There is an enum called LogLevel that represents all the possible values for the logLevel tag. The tags within credentials should all come out as strings. In my class, called DLLConfigFile, I had the following: [XmlElement(ElementName="logLevel", DataType="LogLevel")] public LogLevel LogLevel; However, this isn't going to work because <logLevel> isn't within the root node of the XML file, it's one node deeper in <logging>. How do I go about doing this? As for the <credentials> nodes, my guess is I will need a second class, say CredentialsSection, and have a property such as the following: [XmlElement(ElementName="credentials", DataType="CredentialsSection")] public CredentialsSection[] AllCredentials; Edit: okay, I tried Robert Love's suggestion and created a LoggingSection class. However, my test fails: var xs = new XmlSerializer(typeof(DLLConfigFile)); using (var stream = new FileStream(_configPath, FileMode.Open, FileAccess.Read, FileShare.Read)) { using (var streamReader = new StreamReader(stream)) { XmlReader reader = new XmlTextReader(streamReader); var file = (DLLConfigFile)xs.Deserialize(reader); Assert.IsNotNull(file); LoggingSection logging = file.Logging; Assert.IsNotNull(logging); // fails here LogLevel logLevel = logging.LogLevel; Assert.IsNotNull(logLevel); Assert.AreEqual(EXPECTED_LOG_LEVEL, logLevel); } } The config file I'm testing with definitely has <logging>. Here's what the classes look like: [Serializable] [XmlRoot("logging")] public class LoggingSection : IXmlSerializable { public XmlSchema GetSchema() { return null; } [XmlElement(ElementName="logLevel", DataType="LogLevel")] public LogLevel LogLevel; public void ReadXml(XmlReader reader) { LogLevel = (LogLevel)Enum.Parse(typeof(LogLevel), reader.ReadString()); } public void WriteXml(XmlWriter writer) { writer.WriteString(Enum.GetName(typeof(LogLevel), LogLevel)); } } [Serializable] [XmlRoot("configuration")] public class DLLConfigFile : IXmlSerializable { [XmlElement(ElementName="logging", DataType="LoggingSection")] public LoggingSection Logging; }

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• How do I create a loop based off this array?

  - by dmanexe

  I'm trying to process this array, first testing for the presence of a check, then extrapolating the data from quantity to return a valid price. Here's the input for fixed amounts of items, with no variable quantity. <input type="checkbox" name="measure[<?=$item->id?>][checked]" value="<?=$item->id?>"> <input type="hidden" name="measure[<?=$item->id?>][quantity]" value="1" /> Here's the inputs for variable amounts of items. <input type="checkbox" name="measure[<?=$item->id?>][checked]" value="<?=$item->id?>"> <input class="item_mult" value="0" type="text" name="measure[<?=$item->id?>][quantity]" /> So, the resulting array is multidimensional. Here's an output: Array ( [1] => Array ( [quantity] => 1 ) [2] => Array ( [quantity] => 1 ) [3] => Array ( [quantity] => 1 ) ... [14] => Array ( [checked] => 14 [quantity] => 999 ) ) Here's the loop I'm using to take this array and process items checked off the form in the first place. I guess the question essentially boils down to how do I structure my conditional statement to incorporate the multi-dimensional array? foreach($field as $value): if ($value['checked'] == TRUE) { $query = $this->db->get_where('items', array('id' => $value['checked']))->row(); #Test to see if quantity input is present if ($value['quantity'] == TRUE) { $newprice = $value['quantity'] * $query->price; $totals[] = $newprice; } #Just return the base value if not else { $newprice = $query->price; $totals[] = $newprice; } } else { } ?> <p><?=$query->name?> - <?=money_format('%(#10n', $newprice)?></p> <? endforeach; ?>

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• Fill 4 input with one textarea

  - by Patrice Poliquin

  I have a question for the community. My problem is that I have 4 input files with a maxlength of 60 caracters for a total of 240 caracters. Because the "backend" of the customer's system, it need to be 4 differents inputs max to be inserted and they say it is not user-friendly to fill 4 fields. My solution I want to make a textarea and when you fill it, il complete the 4 fields. [input text #1] max60 [input text #2] max60 [input text #3] max60 [input text #4] max60 [textarea max 240] What I am trying to do is to make by javascript/jQuery to fill up the four field while typing in. At the moment, here is my code. $(document).ready(function() { // My text area $("#inf_notes").bind('keydown', function () { var maxLength = 240; if ($(this).val().length <= 60) { // The first 60 caracters $('#inf_notes_1').val($(this).val()); } if ($(this).val().length > 60 && $(this).val().length <= 120) { // If more then 60, fill the second field $('#inf_notes_2').val($(this).val()); } // If 121 - 180 ... // If 181 - 240 ... if($(this).val().length == 240) { $(this).val($(this).val().substring(0, maxLength)); $('.alert_textarea').show(); // Simple alert else { $('.alert_textarea').hide(); } }); }); It actually works for the first one, but I would like to have some feedbacks to help me complete the script to fill the 3 nexts. Any guess to complete it? -- EDIT #1 I found a way that could maybe work! When the first input is completly filled, it will jump to the next field with a .focus() $(".inf_notes").bind('keydown', function () { var notes1 = $('#inf_notes_1').val(); var notes2 = $('#inf_notes_2').val(); var notes3 = $('#inf_notes_3').val(); if (notes1.length == 60) { $('#inf_notes_2').focus(); } if (notes2.length == 60) { $('#inf_notes_3').focus(); } if (notes3.length == 60) { $('#inf_notes_4').focus(); } });

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• jQuery - Form input return confirm to delete

  - by bruno

  hello guys. I struggled a lot before posting here :) now, I want to replace my default javascript confirmation for deleting a file. I saw a lot of examples here, but no example with form input. Now I have his form: <form action="delete.php" method="post"> <input type="hidden" name="id" value="<{$pid}>" /> <input type="hidden" name="picture" value="<{$lang_del_pic}>" /> <input type="image" src="<{xoImgUrl}>img/del-icon.gif" width="16" height="16" align="bottom" border="0" alt="Delete media" name="pictured" value="<{$lang_del_pic}>" onclick="javascript: return confirm('<{$lang_confirm_del}>');" /> </form> Now, I did everything, I have this div: <div id="dialog-confirm" title="Empty the recycle bin?"> <p><span class="ui-icon ui-icon-alert" style="float:left; margin:0 7px 20px 0;"></span>These items will be permanently deleted and cannot be recovered. Are you sure?</p> </div> this javascript: <script type="text/javascript"> $(document).ready(function() { $("#dialog").dialog({ autoOpen: false, modal: true }); }); $(".confirmLink").click(function(e) { e.preventDefault(); var targetUrl = $(this).attr("href"); $("#dialog").dialog({ buttons : { "Confirm" : function() { window.location.href = targetUrl; }, "Cancel" : function() { $(this).dialog("close"); } } }); $("#dialog").dialog("open"); }); </script> and this new form: <form name="dialog-confirm" id="dialog-confirm" method="post"> <input type="hidden" name="id" value="<{$pid}>" /> <input type="hidden" name="picture" value="<{$lang_del_pic}>" /> <input type="image" src="<{xoImgUrl}>img/del-icon.gif" width="16" height="16" align="bottom" border="0" alt="Delete media" name="pictured" value="" id="opener" /> </form> On press, I call successfuly the jQuery modal diolog, and everything works, but somehow, when I press 'delete all' the script tells me - "the script is called without the necessary parameters" Now I guess I am failig to send the pic ID to be deleted with the jQuery, .. but do not know how to fix it. Any ideas ?

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• Solution Output Directory

  - by L.E.O

  The project that I'm currently working on is being developed by multiple teams where each team is responsible for different part of the project. They all have set up their own C# projects and solutions with configuration settings specific to their own needs. However, now we need to create another, global solution, which will combine and build all projects into the same output directory. The problem that I have encountered though, is that I have found only one way to make all projects build into the same output directory - I need to modify configurations for all of them. That is what we would like to avoid. We would prefer that all these projects had no knowledge about this "global" solution. Each team must retain possibility to work just with their own sub-solution. One possible workaround is to create a special configuration for all projects just for this "global" solution, but that could create extra problems since now you have to constantly sync this configuration settings with the regular one, used by that specific team. Last thing we want to do is to spend hours trying to figure out why something doesn't work when building under global solution just because of some check box that developers have checked in their configuration, but forgot to do so in the global configuration. So, to simplify, we need some sort of output directory setting or post build event that would only be present when building from that global, all-inclusive solution. Is there any way to achieve this without changing something in projects configurations? Update 1: Some extra details I guess I need to mention: We need this global solution to be as close as possible to what the end user gets when he installs our application, since we intend to use it for debugging of the entire application when we need to figure out which part of the application isn't working before sending this bug to the team working on that part. This means that when building under global solution the output directory hierarchy should be the same as it would be in Program Files after installation, so that if, for example, we have Program Files/MyApplication/Addins folder which contains all the addins developed by different teams, we need the global solution to copy the binaries from addins projects and place them in the output directory accordingly. The thing is, the team developing an addin doest necessary know that it is an addin and that it should be placed in that folder, so they cannot change their relative output directory to be build/bin/Debug/Addins.

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• Visual studio 2010 colourizers, intellisense and the rest. Where to start!!

  - by Owen

  Ok, before I begin I realize that there is a lot of documentation on this subject but I have thus far failed to get even basic colourization working for VS2010. My goal is to simply get to a point where I can open a document and everything is coloured red, from here I can implement the relevant parsing logic. Here's what I have tried/found: 1) Downloaded all the relevent SDK's and such- Found the ook sample (http://code.msdn.microsoft.com/ookLanguage) - didn't build, didn't work. 2) Knowing almost nothing about MEF read through "Implementing a Language Service By Using the Managed Package Framework" - http://msdn.microsoft.com/en-us/library/bb166533(v=VS.100).aspx This was pretty much a copy and paste of all the basic stuff here, and also updating some references which were out of date with the sample see: http://social.msdn.microsoft.com/Forums/en-US/vsx/thread/a310fe67-afd2-4592-b295-3fc86fec7996 Now, I have got to a point where when running the package MEF appears to have hooked up correctly (I know this because with the debugger open I can see that the packages initialize and FDoIdle methods are being hit). When I open a file of the extension I have registered with the ProvideLanguageExtensionAttribute everything dies as if in an endless loop, yet no debug symbols hit (though they are loaded). Looking at the ook sample and the MEF examples they seem to be totally different approaches to the same problem. In the ook sample there are notions of Clasifications and Completion controllers which aren't mentioned in the MEF example. Also, they don't seem to create a Package or Language service, so I have no idea how it should work? With the MEF example, my assumption is that I need to hook into the "IScanner.ScanTokenAndProvideInfoAboutIt" to provide syntax highlighting? Which would be fine if I could ever hit this method. So my first question I guess is which approach should I be taking here? Or do they both somehow tie together? My second questions is, where can I find a basic fully working project that implements bog standard basic syntax highlighting and intellisense or VS2010? Thirdly, in the MEF example when I created a Package there were a bunch of test projects created for me. I appears that the integration tests launch the VS2010 test rig somehow, but the test fails. It would be good to write my service with tests but I have no idea what/how I can test each interaction so any references to testing Language services would be helpful. Finally, please throw any resource/book links my way that I may find useful. Cheers, Chris. N.B. Sorry I realize this is part question part rant, but I have never been so confused.

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• Why does std::map operator[] create an object if the key doesn't exist?

  - by n1ck

  Hi, I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there either) but a quick search here doesn't seem to find it so here it is: Why does the std::map operator[] create an object if the key doesn't exist? I don't know but for me this seems counter-intuitive if you compare to most other operator[] (like std::vector) where if you use it you must be sure that the index exists. I'm wondering what's the rationale for implementing this behavior in std::map. Like I said wouldn't it be more intuitive to act more like an index in a vector and crash (well undefined behavior I guess) when accessed with an invalid key? Refining my question after seeing the answers: Ok so far I got a lot of answers saying basically it's cheap so why not or things similar. I totally agree with that but why not use a dedicated function for that (I think one of the comment said that in java there is no operator[] and the function is called put)? My point is why doesn't map operator[] work like a vector? If I use operator[] on an out of range index on a vector I wouldn't like it to insert an element even if it was cheap because that probably mean an error in my code. My point is why isn't it the same thing with map. I mean, for me, using operator[] on a map would mean: i know this key already exist (for whatever reason, i just inserted it, I have redundancy somewhere, whatever). I think it would be more intuitive that way. That said what are the advantage of doing the current behavior with operator[] (and only for that, I agree that a function with the current behavior should be there, just not operator[])? Maybe it give clearer code that way? I don't know. Another answer was that it already existed that way so why not keep it but then, probably when they (the ones before stl) choose to implement it that way they found it provided an advantage or something? So my question is basically: why choose to implement it that way, meaning a somewhat lack of consistency with other operator[]. What benefit do it give? Thanks

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