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• Deriving streambuf or basic_ostringstream?

  - by Helltone

  Hi, I want to derive a stringstream so that I can use the operator<< to construct a message which will then be thrown. The API would look like: error("some text") << " more text " << 42 << std::endl; This should do a throw "some text more text 42" So what I did is make an errorbuf (inheriting from streambuf) which overloads the 'overflow' method and then create an ostream(&errorbuf). I wonder if I shouldn't instead inherit from basic_ostringstream or something...

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• LINQ Expression<Func<T, bool>> equavalent of .Contains()

  - by BK

  Has anybody got an idea of how to create a .Contains(string) function using Linq Expressions, or even create a predicate to accomplish this public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2) { var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); return Expression.Lambda<Func<T, bool>> (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters); } Something simular to this would be ideal?

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• Caesar Cipher in Java (Spanish Characters)

  - by Rodolfo

  I've reading this question, and I was wondering if Is there any way to consider the whole range of characters? For example, "á", "é", "ö", "ñ", and not consider " " (the [Space])? (For example, my String is "Hello World", and the standard result is "Khoor#Zruog"; I want to erase that "#", so the result would be "KhoorZruog") I'm sure my answer is in this piece of code: if (c >= 32 && c <= 127) { // Change base to make life easier, and use an // int explicitly to avoid worrying... cast later int x = c - 32; x = (x + shift) % 96; chars[i] = (char) (x + 32); } But I've tried some things, and it didn't work.

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• Findbugs warning: Equals method should not assume anything about the type of its argument

  - by Uri

  When running FindBugs on my project, I got a few instances of the error described above. Namely, my overriding versions of equals cast the RHS object into the same type as the object in which the overriding version is defined. However, I'm not sure whether a better design is possible, since AFAIK Java does not allow variance in method parameters, so it is not possible to define any other type for the equals parameter. Am I doing something very wrong, or is FindBugs too eager? A different way to phrase this question is: what is the correct behavior if the object passed to equals is not the same type as an LHS: Is this a false, or should there be an exception? For example: public boolean equals(Object rhs) { MyType rhsMyType = (MyType)rhs; // Should throw exception if(this.field1().equals(rhsMyType.field1())... // Or whatever }

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• How can I access IEnumerable<T> extension methods on my custom subclass of BindingList<T>?

  - by Dan

  I have a custom subclass of BindingList<T> that I want to execute a LINQ query over using the handy extension methods. For example: public int GetSum(MyList<T> list) { return list.Sum(x => x.Value); } But the compiler complains that it can't resolve Sum because it doesn't recognize list as an IEnumerable<T>, which it obviously is, because this works: public int GetSum(MyList<T> list) { return ((IEnumerable<T>)list).Sum(x => x.Value); } Anyone have a clever way I can avoid the ugly and unecessary cast?

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• Haskell: What is the difference between $ (dollar) and $! (dollar exclamation point)

  - by Jelle Fresen

  Can anybody explain the difference in Haskell between the operators ($) and ($!) (dollar sign vs dollar sign exclamation point)? I haven't seen the use of $! anywhere so far, but while browsing through the Haskell reference on www.zvon.org, I noticed its existence and that it has the exact same definition as $. When trying some simple statements in a Haskell interpreter (ghci), I couldn't find any difference, nor could I find any reference to the operator in the top listed tutorials when googling for haskell tutorial. So, just out of curiosity, what is the difference, if at all?

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• Alternative to c++ static virtual methods

  - by Jaime Pardos

  In C++ is not possible to declare a static virtual function, neither cast a non-static function to a C style function pointer. Now, I have a plain ol' C SDK that uses function pointers heavily. I have to fill a structure with several function pointers. I was planning to use an abstract class with a bunch of static pure virtual methods, and redefine them in derived classes and fill the structure with them. It wasn't until then that I realized that static virtual are not allowed in C++. Is there any good alternative? The best I can think of is defining some pure virtual methods GetFuncA(), GetFuncB(),... and some static members FuncA()/FuncB() in each derived class, which would be returned by the GetFuncX(). Then a function in the abstract class would call those functions to get the pointers and fill the structure.

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• Is it OK to open a DB4o file for query, insert, update multiple times?

  - by Khnle

  This is the way I am thinking of using DB4o. When I need to query, I would open the file, read and close: using (IObjectContainer db = Db4oFactory.OpenFile(Db4oFactory.NewConfiguration(), YapFileName)) { try { List<Pilot> pilots = db.Query<Pilot>().ToList<Pilot>(); } finally { try { db.Close(); } catch (Exception) { }; } } At some later time, when I need to insert, then using (IObjectContainer db = Db4oFactory.OpenFile(Db4oFactory.NewConfiguration(), YapFileName)) { try { Pilot pilot1 = new Pilot("Michael Schumacher", 100); db.Store(pilot1); } finally { try { db.Close(); } catch (Exception) { }; } } In this way, I thought I will keep the file more tidy by only having it open when needed, and have it closed most of the time. But I keep getting InvalidCastException Unable to cast object of type 'Db4objects.Db4o.Reflect.Generic.GenericObject' to type 'Pilot' What's the correct way to use DB4o?

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• Storing multiple checkbox values in database

  - by Madjokr

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

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• Get a list of documents from Mongo DB

  - by Andrei Neagu

  Hello, I want to do something like this: List<int> fff = new List<int>(); fff.Add(1); fff.Add(2); fff.Add(5); Mongo m = new Mongo(); m.Connect(); var dataBase = m.GetDatabase("database"); var collection = dataBase.GetCollection("coll"); IMongoQuery queryable = collection.AsQueryable(); MongoQueryProvider prov = new MongoQueryProvider(collection); var query = new MongoQuery(prov); var ffppp = from p221 in query where fff.Contains((int)p221["oid"]) select p221; This throws this error : The method 'Contains' could not be converted into a constant. I saw that mongo has an operator $in. Does any one know how can I use it from c#? (http://www.mongodb.org/display/DOCS/Advanced+Queries) Thanks

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• Nhibernate Exception - Return types of SQL query were not specified

  - by Muhammad Akhtar

  I am executing SQL in hibernate and getting exception Return types of SQL query were not specified public ArrayList get(string Release, int DocId) { string query = string.Format("select ti.Id, (' Defect ' + cast(ti.onTimeId as varchar) + ' - ' + ti.Name) as Name from TrackingItems ti inner join DocumentTrackingItems dti on ti.Id = dti.ItemStepId inner join Documents doc on dti.DocumentId = doc.Id where ti.ReleaseId = '{0}' AND doc.TypeId = {1} and Doc.Name is null AND ti.Type = 'Defect'", Release, DocId); ISession session = NHibernateHelper.GetCurrentSession(); ArrayList arList = (ArrayList)session.CreateSQLQuery(query).List(); return arList; } When I run this query in SQL, it working fine. any idea what could be the issue? -------- Thanks.........

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• how to get the size of a C global array into an assembly program written for the avr architecture co

  - by johannes

  I have a .c file with the following uint8_t buffer[32] I have a .S file where I want to do the following cpi r29, buffer+sizeof(buffer) The second argument for cpi muste be an imidiate value not a location. But unfortunetly sizeof() is a c operator. Both files, are getting compiled to seperate object files and linked afterwards. If I do avr-objdump -x file.c. Amongst other things, I get the size of the buffer. So it is already available in the object file. How do I access the size of the buffer in my assembly file at compile time?

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• C# implicit conversions

  - by Chris Boden

  Hello, I'm currently working on an application where I need to load data from an SQL database and then assign the retrieved values into the properties of an object. I'm doing this by using reflection since the property names and column names are the same. However, many of the properties are using a custom struct type that is basically a currency wrapper for the decimal type. I have defined an implicit conversion in my struct: public static implicit operator Currency(decimal d) { return new Currency(d); } This works fine when I use it in code. However, when I have this: foreach (PropertyInfo p in props) { p.SetValue(this, table.Rows[0][p.Name], null); } It throws an ArgumentException stating that it cannot convert from System.Decimal to Currency. I'm confused since it works fine in any other circumstance.

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• Warning: XXX may not respond to YYY

  - by Aurel300

  Hey, I am making some stuff in Objective-C++... And I must say that I am a total newbie when it comes to the Objective-C part... I don't really want to learn it, I kinda just need it for accessing a few Mac APIs (ObjC is such a dumb language). So - compiling with g++ -x objective-c++ - and I somehow keep getting this warning: XXX may not respond to YYY First it was with a NSScreen, now it is with a NSWindow: NSWindow may not respond to +initWithContentRect:styleMask:backing:defer: I saw somewhere that I should cast it to id, but didn't work, throwing absolutely cryptic errors... So - WHAT does this warning actually mean and HOW am I supposed to make it stop?

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

  - by Robert S. Barnes

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

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• match at the beginning of any line, including the first

  - by JoelFan

  According the the Perl documentation on regexes: By default, the "^" character is guaranteed to match only the beginning of the string ... Embedded newlines will not be matched by "^" ... You may, however, wish to treat a string as a multi-line buffer, such that the "^" will match after any newline within the string ... you can do this by using the /m modifier on the pattern match operator. The "after any newline" part means that it will only match at the beginning of the 2nd and subsequent lines. What if I want to match at the beginning of any line (1st, 2nd, etc.)?

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• readobject method throws ClassNotFoundException

  - by eruina

  Hi all, I'm trying to pick up Java and wanted to test around with Java's client/server to make the client send a simple object of a self defined class(Message) over to the server. The problem was that I kept getting a ClassNotFoundException on the server side. I think the rest of the codes seem to be alright because other objects such as String can go through without problems. I had two different netbeans projects in different locations for client and server each. Each of them have their own copy of Message class under their respective packages. Message class implements Serializable. On the client side, I attempt to send a Message object through. On the server side, upon calling the readObject method, it seems to be finding Message class from the client's package instead of it's own. printStackTrace showed: "java.lang.ClassNotFoundException: client.Message" on the server side I have not even tried to cast or store the object received yet. Is there something I left out?

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• Google Datastore low-level api query by key property

  - by Keyur

  I'm using the low-level google datastore api and I want to query by the key property and another property (let's call it category). I need to query based on a list of keys for which I'll use the IN operator. I know that the max. number of values you can provide for the IN clause is 30. I have 2 questions: Does the limit of 30 IN values apply to the key property as well? Do I need to create a composite index on {_key_ + category} or just on {category} for this query? Thanks, Keyur

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• How can I search for numbers in a varchar column

  - by dave

  I've got a simple nvarchar(25) column in an SQL database table. Most of the time, this field should contain alphanumeric text. However, due to operator error, there are many instances where it contains only a number. Can I do a simple search in SQL to identify these cases? That is, determine which rows in the table contain only digits in this column. As an extension, could I also search for those column values which contain only digits and a space and/or slash. In other languages (eg. Perl, Java) a regular expression would resolve this quickly and easily. But I haven't been able to find the equivalent in SQL.

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• matlab noninteger step indexing

  - by rlbond

  So, I have a vector: k = 1:100; And I want to take 19 elements from it, which are roughly equally-spaced. So I write this: m = k(1:(99/18):end); This works great, except for a tiny problem: Warning: Integer operands are required for colon operator when used as index m = 1 7 12 18 23 29 34 40 45 51 56 62 67 73 78 84 89 95 100 Now, I understand why this comes up, but I'd like to get rid of that warning. Is there a "right" way to do this without a warning?

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• Getting error in MVC Proj while writing Lambda Expression

  - by Shrewd Demon

  hi, i am creating a sample movie (MVC) application. I was getting fine with Viewing and Creating a new record, but when i wrote the code to get the details of a particular record i met with the following error: Unable to cast objec`t of type 'System.Data.Objects.ObjectQuery`1[MovieApp.Models.Movie]' to type 'MovieApp.Model`s.Movie'. here is the code i wrote for getting the details public ActionResult Details(int id) { var moviedetail = (Movie)_entities.MovieSet.Where(mvid => mvid.Id == id); return View(moviedetail); } can any body tell me whats going wrong and where ?? thank you.

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• Does the JPQL avg aggregate function work with Integers?

  - by Kyle Renfro

  I have a JPA 2 Entity named Surgery. It has a member named transfusionUnits that is an Integer. There are two entries in the database. Executing this JPQL statement: Select s.transfusionUnits from Surgery s produces the expected result: 2 3 The following statement produces the expected answer of 5: Select sum(s.transfusionUnits) from Surgery s I expect the answer of the following statement to be 2.5, but it returns 2.0 instead. Select avg(s.transfusionUnits) from Surgery s If I execute the statement on a different (Float) member, the result is correct. Any ideas on why this is happening? Do I need to do some sort of cast in JPQL? Is this even possible? Surely I am missing something trivial here.

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• How can I match at the beginning of any line, including the first, with a Perl regex?

  - by JoelFan

  According the the Perl documentation on regexes: By default, the "^" character is guaranteed to match only the beginning of the string ... Embedded newlines will not be matched by "^" ... You may, however, wish to treat a string as a multi-line buffer, such that the "^" will match after any newline within the string ... you can do this by using the /m modifier on the pattern match operator. The "after any newline" part means that it will only match at the beginning of the 2nd and subsequent lines. What if I want to match at the beginning of any line (1st, 2nd, etc.)? EDIT: OK, it seems that the file has BOM information (3 chars) at the beginning and that's what's messing me up. Any way to get ^ to match anyway? EDIT: So in the end it works (as long as there's no BOM), but now it seems that the Perl documentation is wrong, since it says "after any newline"

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• Placement new in gcc

  - by Roman Prikhodchenko

  I need to find a workaround for a bug with placement new in g++. I now it was fixed in gcc-4.3 but I have to support versions 4.2 and 4.1. For example, following code compiles with an error "error: no matching function for call to 'operator new(long unsigned int, void*&)" template<class T, template<typename> class Alloc> inline void* type_ctor() { Alloc<T> a; void* p = a.allocate(1); new(p) T; return p; } ..... type_ctor<A, NewAllocator >();

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• PHP - Loop thru recordset and fire event each n rows

  - by Luciano

  I'm looking for the right logic to loop thru a recordset and fire an event each n times. Searching on Google i've found some discussion on similar situations, but it seems that solutions don't fits my needs. Let's say i have a recordset of 22 rows. I want to loop thru each row and launch a function on the 4th, the 8th, the 12th and so on... Using the modulus operator as shown in this answer, if($i % 4 == 0), i get the event fired each 4 rows, but 22 its not a multiple of 4 so the event is fired till the 20th row and then nothing. Maybe i need to make a division counting rows in 'excess'? Since the recordset will be between 50 and 200 rows i think its not necessary run multiple query of 4 rows, am I wrong? Thanks in advance!

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