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• Sending files using Winsock - optimal send() data length?

  - by Meta

  I am using Winsock with non-blocking sockets to send a file to a client. The way I'm doing it right now is that I read a chunk of 8192 bytes from the file, and then loop until all of it successfully goes through send() (obviously handling WSAEWOULDBLOCK as it occurs). I then move on and read the next 8192 bytes, and so on... Although I can use any other number than 8192 when I test the transfer on my local machine, once I try it over a network, it seems like 8191 is the largest number I can use. When I try to use any number higher than 8191 (starting with 8192), the file transfer becomes extremely slow (about 5 times slower). Is there any reason why 8191 is so special? I've done some more testing and it turns out that using 8000 is slightly faster (by 0.5%). If you understand why 8191 is so special, can you tell me if there is a number better than the others (better than 8000)? I have a feeling that it has something to do with the fact that the default send buffer allocated to the socket by Winsock is 8KB, but I don't understand why. It might also have something to do with the Nagle algorithm, but again, I'm not sure how. Note that I have not modified the SO_SNDBUF option nor the TCP_NODELAY option. Or am I doing this all wrong? What's the best way of sending a file over a non-blocking socket?

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• Data-annotation getting errormessage out database

  - by Masna

  Hello, With asp.net mvc you can use the annotation [Required (errormessage="This is required")] How can I create something like this: [Required (errormessage="ERRORXX")] So I can look up in a database what this ERRORXX is and display it on my form. Now my form displays ERRORXX. How can I create something that solves my problem? Thx!

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• How to structure a database with questions and answers?

  - by Andreas Johannessen

  Hi I am going to make a simple application that uses a database. I could need some guidance on how to structure it. I shall make question program. What I have in mind is. One table with questions One table with the difficulity of the question One table with the category of the question However, what do I do with the answers? Have them as seperate columns in the question-table? It sounds like a bad practice.(Also, where do I have the correct answer) Each question will have 5 answers where only one of them is correct.

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• Modifying C# dictionary value

  - by minjang

  I'm a C++ expert, but not at all for C#. I created a Dictionary<string, STATS>, where STATS is a simple struct. Once I built the dictionary with initial string and STATS pairs, I want to modify the dictionary's STATS value. In C++, it's very clear: Dictionary<string, STATS*> benchmarks; Initialize it... STATS* stats = benchmarks[item.Key]; // Touch stats directly However, I tried like this in C#: Dictionary<string, STATS> benchmarks = new Dictionary<string, STATS>(); // Initialize benchmarks with a bunch of STATS foreach (var item in _data) benchmarks.Add(item.app_name, item); foreach (KeyValuePair<string, STATS> item in benchmarks) { // I want to modify STATS value inside of benchmarks dictionary. STATS stat_item = benchmarks[item.Key]; ParseOutputFile("foo", ref stat_item); // But, not modified in benchmarks... stat_item is just a copy. } This is a really novice problem, but wasn't easy to find an answer. EDIT: I also tried like the following: STATS stat_item = benchmarks[item.Key]; ParseOutputFile(file_name, ref stat_item); benchmarks[item.Key] = stat_item; However, I got the exception since such action invalidates Dictionary: Unhandled Exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute. at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext() at helper.Program.Main(String[] args) in D:\dev\\helper\Program.cs:line 75

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• C: getopt with list of acceptable optarg. What is the best practise ?

  - by Xavier Maillard

  Hi, I am writing a C program which is a frontend to a myriad tools. This fronted will be launched like this: my-frontend --action <AN ACTION> As all the tools have the same prefix, let say for this example this prefix is "foo". I want to concatenate "AN ACTION" to this prefix and exec this (if the tool exists). I have written something but my implementation uses strcmp to test that "AN ACTION" is a valid action. Even if this works, I do not like it. So I am looking for a nicer solution that would do the same. The list of possibilities is pretty small (less than 10) and static (the list is "hardcoded") but I am sure there is a more "C-ish" way to do this (using a struct or something like that). As I am not a C expert, I am asking for your help. Regards

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• Send data from Service to Widget on Android.

  - by Jose Vega

  I am writing a widget on Android 1.6 that shows the minutes that a person has used on the current month. The way I have it setup is by having a service that listens to the state of the phone and when the phone is picked up, it starts the timer and when the person hangs up, ends a timer. I would like to send this variable(long duration) over to my appWidgetProvider so I could update the edit text on it.

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• How do I find all paths through a set of given nodes in a DAG?

  - by Hanno Fietz

  I have a list of items (blue nodes below) which are categorized by the users of my application. The categories themselves can be grouped and categorized themselves. The resulting structure can be represented as a Directed Acyclic Graph (DAG) where the items are sinks at the bottom of the graph's topology and the top categories are sources. Note that while some of the categories might be well defined, a lot is going to be user defined and might be very messy. Example: On that structure, I want to perform the following operations: find all items (sinks) below a particular node (all items in Europe) find all paths (if any) that pass through all of a set of n nodes (all items sent via SMTP from example.com) find all nodes that lie below all of a set of nodes (intersection: goyish brown foods) The first seems quite straightforward: start at the node, follow all possible paths to the bottom and collect the items there. However, is there a faster approach? Remembering the nodes I already passed through probably helps avoiding unnecessary repetition, but are there more optimizations? How do I go about the second one? It seems that the first step would be to determine the height of each node in the set, as to determine at which one(s) to start and then find all paths below that which include the rest of the set. But is this the best (or even a good) approach? The graph traversal algorithms listed at Wikipedia all seem to be concerned with either finding a particular node or the shortest or otherwise most effective route between two nodes. I think both is not what I want, or did I just fail to see how this applies to my problem? Where else should I read?

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• Efficient storage/retrieval method for replayable comet style applications (Google Wave, Etherpad)

  - by Gareth Simpson

  I am considering a web application that would have the same kind of multi user, automatic saving, infinite undo / replay capabilities that you see in Google Wave and Etherpad (albeit on a drastically smaller scale and userbase). Before I go away and reinvent the wheel, is this something that has already been addressed as either a piece of technology or library, or even just a design pattern. I know this isn't necessarily the best Stack Overflow question as there is probably not a "right" answer, but my Google-fu has failed me and I'd just like a reading list! Ordinarily I would be developing under python/django but this is not a firm requirement just a preference :)

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• How to bind a complex dictionary to a Gridview in asp.net?

  - by Mehdi

  I've used an early binding of a dictionary<string, string> to a gridview to show Urls Text and its HRef as key-value and it works like a charm. But since I want to replace the dictionary with this one : dictionary<string, LinkInfo> the binding goes wrong! Should I handle some events like as onItemDataBound or something? and the LinkInfo structure is: public struct LinkInfo{ public string href; public bool Enabled; }

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• Unit Testing Model Classes that derive from NSManagedObject

  - by Matt Baker

  So...I'm trying to get unit tests set up in my iPhone App but I'm having some issues. I'm trying to test my model classes but they inherit directly from NSManagedObject. I'm sure this is a problem but I don't know how to get around it. Everything is building and running as expected but I get this error when calling any method on the class I'm testing: Unknown.m:0:0 unrecognized selector sent to instance 0xc2b120 If I follow this structure (http://chanson.livejournal.com/115621.html) to create my object in my tests I end up with another error entirely but it still doesn't help me. Basically my question is this: how can I test a class that inherits from NSManagedObject?

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• javascript table - update on data request

  - by flyingcrab

  Hi, I am trying to update a table based on a json request. The first update / draw works fine - but any subsequent changes to the variables (the start and end date) do not show up - even though the json pulled from the server seems to be correct (according to firebug). AFAIK the code below should re-initialize everything - no sure what is going on (I'm using the Google vizulization api)? function handleQueryResponse(response) { if (response.isError()) { //alert('Error in query: ' + response.getMessage() + ' ' + response.getDetailedMessage()); return; } visualization = new google.visualization.Table(document.getElementById('visualization')); visualization.draw(response.getDataTable(), null); } One more thing: I'm working on a page that displays textbased tables and currently trying to decide between the google table (viz api) and a jQuery alternative I came across jqGrid any good ones I am missing?

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• String or binary data would be truncated -- Heisenberg problem

  - by harpo

  When you get this error, the first thing you ask is, which column? Unfortunately, SQL Server is no help here. So you start doing trial and error. Well, right now I have a statement like: INSERT tbl (A, B, C, D, E, F, G) SELECT A, B * 2, C, D, E, q.F, G FROM tbl ,othertable q WHERE etc etc Note that Some values are modified or linked in from another table, but most values are coming from the original table, so they can't really cause truncation going back to the same field (that I know of). Eliminating fields one at a time eventually makes the error go away, if I do it cumulatively, but — and here's the kicker — it doesn't matter which fields I eliminate. It's as if SQL Server is objecting to the total length of the row, which I doubt, since there are only about 40 fields in all, and nothing large. Anyone ever seen this before? Thanks. UPDATE: I have also done "horizontal" testing, by filtering out the SELECT, with much the same result. In other words, if I say WHERE id BETWEEN 1 AND 100: Error WHERE id BETWEEN 1 AND 50: No error WHERE id BETWEEN 50 AND 100: No error I tried many combinations, and it cannot be limited to a single row.

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• [Cocoa] Temporarily disabled NSArrayController filterPredicate, or consult ManagedObjectContext?

  - by ndg

  I have an NSArrayController which is bound to a class in my Managed Object Context. During runtime the NSArrayController can have a number of different filter predicates applied. At certain intervals, I want to iterate through my NSArrayController's contents regardless of the filter predicate applied to it. To do this, I set the filterPredicate to nil and then reinstate it after having iterated through my array. This seems to work, but I'm wondering if it's best practice? Should I instead be polling my Managed Object Context manually? NSPredicate *predicate = nil; predicate = [myArrayController filterPredicate]; [myArrayController setFilterPredicate:nil]; for(MyManagedObject *object in [myArrayController arrangedObjects]) { // ... } [myArrayController setFilterPredicate:predicate];

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• about the usage of mudolus operator

  - by matin1234

  Hi this a part of code for Quick Sort algorithm but realy I do not know that why it uses rand() %n please help me thanks Swap(V,0,rand() %n) // move pivot elem to V[0]

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• Leak in managedObjectContext save:

  - by Kamchatka

  Hi I have the following piece of code and when I use Instruments/Object Allocations, it tells me that there is a leak there (which goes down to sqlite3MemMalloc). Is there something that I should release? if (![managedObjectContext save:&error]) { NSLog(@"Error while saving."); } The save works well and doesn't trigger an error.

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• Easiest Way to Parse data from twitter with Cocoa

  - by happyCoding25

  Hello, I've followed the tutorial from here: Twitter Client Tutorial to make a little twitter app. Now I need to find out how to parse the XML twitter gives you when you make a request. I've looked at tons of tutorials on phrasing xml on the iPhone but none have made much sense because Im still new to cocoa. Twitter stores the text of the tweet in something like this <text> Some tweet here </text>. From reading the tutorials I think this would involve nsxmlparser but I'm not sure. If anyone could share some code that could parse the <text> Some tweet here </text> things into an array that would be really great. Thanks in advance

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• advanced python autovivification

  - by Zhang18

  This question is about implementing the full PERL autovivification in python. I know similary questions were asked before and so far the best answre is http://stackoverflow.com/questions/635483/what-is-the-best-way-to-implement-nested-dictionaries-in-python/652284#652284. However, I'm looking to do this: a['x']['y'].append('z') without declaring a['x']['y'] = [] first, or rather, not declaring a['x'] = {} either. I know dict and list classes sorta don't mix so this is hard, but I'm interested in seeing if someone has an ingenius solution probably involving creating an inherited class from dict but defined a new append method on it? I also know this might throw off some python purists who will ask me to stick with Perl. But even just for a challenge, I'd like to see something. thx!

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• Calculated group-by fields in MongoDB

  - by Navin Viswanath

  For this example from the MongoDB documentation, how do I write the query using MongoTemplate? db.sales.aggregate( [ { $group : { _id : { month: { $month: "$date" }, day: { $dayOfMonth: "$date" }, year: { $year: "$date" } }, totalPrice: { $sum: { $multiply: [ "$price", "$quantity" ] } }, averageQuantity: { $avg: "$quantity" }, count: { $sum: 1 } } } ] ) Or in general, how do I group by a calculated field?

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• SQL Server Cursor data as result of stored procedure

  - by Dmitry Borovsky

  Hello, I have a stored procedure DECLARE cursor FOR SELECT [FooData] From [FooTable]; OPEN cursor ; FETCH NEXT FROM cursor INTO @CurrFooData; WHILE @@FETCH_STATUS = 0 BEGIN SELECT @CurrFooData AS FooData; INSERT INTO Bar (BarData) VALUES(@CurrFooData); FETCH NEXT FROM cursor INTO @CurrFooData; END; CLOSE cursor DEALLOCATE cursor But in result I have a lot of tables, not one. How can I return one table with 'FooData' column and all '@CurrFooData' rows?

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• Can I configure AutoMapper to read from custom column names when mapping from IDataReader?

  - by rohancragg

  Psuedo code for mapping configuration (as below) is not possible since the lambda only lets us access Type IDataReader, wheras when actually mapping, AutoMapper will reach into each "cell" of each IDataRecord while IDataReader.Read() == true: var mappingConfig = Mapper.CreateMap<IDataReader, IEnumerable<MyDTO>>(); mappingConfig.ForMember( destination => destination.???, options => options.MapFrom(source => source.???)); Can anyone think of a way to do this using AutoMapper configuration at runtime or just some other dynamic approach that meets the requirement below. The requirement is to support any incoming IDataReader which may have column names that don't match the property names of MyDTO and there is no naming convention I can rely on. Instead we'll ask the user at runtime to cross-reference the expected column names with the actual column names found in the IDataReader via IDataReader.GetSchemaTable().

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• How can I compare two sets of data in linq and return the common data?

  - by kjm

  I have two IList<string> a and b. I want to find out what strings are in both a and b using LINQ.

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• JQuery Autocomplete - Stop mouseover+Return submitting data

  - by ILT

  I'm using JQuery Autocomplete (bassistance) and have run into a problem. If the mouse rolls over one of the autocomplete suggestions and the user hits the return key (rather than clicking to make selection), the form is submitted and goes to whatever link was rolled over at the time. This is a problem as people click in the textbox, and when typing their search, leave the pointer where the autocomplete popup appears. So when they hit enter, it doesn't do the search for whatever they typed in the box but whatever was highlighted in the autocomplete suggestions. Is there a way to stop this? Using Google as the functionality I'm after... So just to clarify - I want selections via mouse and keyboard to go to the same place, but if the UP or DOWN arrow has not been pressed (user not selected an autocomplete option via the keyword), dont go to the URL specified in the autosuggest - instead submit the form (traditional method without JQuery) based on what has been typed in the textbox. I hope I'm explaining this clearly? :S

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• Circular buffer in JavaScript

  - by lonforce

  I was wondering whether anyone has already implemented a circular buffer in JavaScript? How would you do that without having pointers?

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• Implementing simple business model in Haskell

  - by elmes

  Supose we have a very simple model: Station has at least one Train Train has at least two Stations The model has to allow to check what stations any given train visits and to check what trains visit a particular station. How to model it in Haskell? I am a Haskell newbie, so please correct me: once an object is created, you cannot modify it - you can only make a new object based on that one (~immutability). Am I right? If so, I'll have to create a lot of temporary variables with semi-initialized objects (during deserialization or even in unit tests). Basically what I need is an example of modeling domain classes in Haskell - after reading "Learn you a haskell.." I still have no idea how to use this language.

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• array of structures, or structure of arrays?

  - by Jason S

  Hmmm. I have a table which is an array of structures I need to store in Java. The naive don't-worry-about-memory approach says do this: public class Record { final private int field1; final private int field2; final private long field3; /* constructor & accessors here */ } List<Record> records = new ArrayList<Record>(); If I end up using a large number ( 106 ) of records, where individual records are accessed occasionally, one at a time, how would I figure out how the preceding approach (an ArrayList) would compare with an optimized approach for storage costs: public class OptimizedRecordStore { final private int[] field1; final private int[] field2; final private long[] field3; Record getRecord(int i) { return new Record(field1[i],field2[i],field3[i]); } /* constructor and other accessors & methods */ } edit: assume the # of records is something that is changed infrequently or never I'm probably not going to use the OptimizedRecordStore approach, but I want to understand the storage cost issue so I can make that decision with confidence. obviously if I add/change the # of records in the OptimizedRecordStore approach above, I either have to replace the whole object with a new one, or remove the "final" keyword. kd304 brings up a good point that was in the back of my mind. In other situations similar to this, I need column access on the records, e.g. if field1 and field2 are "time" and "position", and it's important for me to get those values as an array for use with MATLAB, so I can graph/analyze them efficiently.

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