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• std::map default value for build-in type

  - by Qifa Zhao

  Recently, I was confused by the std::map operator[] function. In the MSDN library, it says: "If the argument key value is not found, then it is inserted along with the default value of the data type." I tryed to search much more exactly explanation for this issue. For example here: std::map default value In this page, Michael Anderson said that "the default value is constructed by the default constructor(zero parameter constructor)". Now my quest comes to this:"what the default value for the build-in type?". Was it compiler related? Or is there a standard for this issue by the c++ stardard committee? I did a test on visual studio 2008 for the "int" type, and found the "int" type is construted with the value 0.

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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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• How to read from a method that returns a filehandle in perl?

  - by Ryan Thompson

  I have an object with a method that returns a filehandle, and I want to read from that handle. The following doesn't work, because the right angle bracket of the method call is interpreted as the closing angle bracket of the input reader: my $input = <$object->get_handle()>; That gets parsed as: my $input = ( < $object- > ) get_handle() >; which is obviously a syntax error. Is there any way I can perform a method call within an angle operator, or do I need to break it into two steps like this? my $handle = $object->get_handle(); my $input = <$handle>;

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• Subscribing to a ObservableCollection via reflection

  - by Julian Lettner

  How can I subscribe to a ObservableCollection<??> without knowing the element type of the collection? Is there a way to do this without too many 'magic strings'? This is a question for the .NET version 3.5. I think 4.0 would make my life much easier, right? Type type = collection.GetType(); if(type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ObservableCollection<>)) { // I cannot cast the collection here ObservableCollection<object> x = collection; } Thanks for your time.

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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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• Excel VBA to check autofilter for data

  - by cav719

  I need help checking for autofiltered rows not including the header. I want it to give a message box "No records found." then exit sub or continue with copy paste if there are rows beyond the header row. I know I need an If/Else entry after the filter to check for data but I'm having trouble figuring how to check. This code is being done from a UserForm I created. Here is my script: Private Sub Searchbycompanyfield_Click() If CompanyComboBox1.Value = "" Then MsgBox "Please enter a Company to begin search." Exit Sub End If ActiveSheet.Range("$A:$H").AutoFilter Field:=1, Criteria1:=EQDataEntry.CompanyComboBox1.Value, Operator:=xlOr Cells.Select Selection.Copy Sheets("Sheet2").Select Range("A5").Select ActiveSheet.Paste Call MessageBoxYesOrNoMsgBox End Sub Any help would be greatly appreciated.

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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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• 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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• Method hiding with interfaces

  - by fearofawhackplanet

  interface IFoo { int MyReadOnlyVar { get; } } class Foo : IFoo { int MyReadOnlyVar { get; set; } } public IFoo GetFoo() { return new Foo { MyReadOnlyVar = 1 }; } Is the above an acceptable way of implementing a readonly/immutable object? The immutability of IFoo can be broken with a temporary cast to Foo. In general (non-critical) cases, is hiding functionality through interfaces a common pattern? Or is it considered lazy coding? Or even an anti-pattern?

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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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• 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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• In Haskell, how can you sort a list of infinite lists of strings?

  - by HaskellNoob

  So basically, if I have a (finite or infinite) list of (finite or infinite) lists of strings, is it possible to sort the list by length first and then by lexicographic order, excluding duplicates? A sample input/output would be: Input: [["a", "b",...], ["a", "aa", "aaa"], ["b", "bb", "bbb",...], ...] Output: ["a", "b", "aa", "bb", "aaa", "bbb", ...] I know that the input list is not a valid haskell expression but suppose that there is an input like that. I tried using merge algorithm but it tends to hang on the inputs that I give it. Can somebody explain and show a decent sorting function that can do this? If there isn't any function like that, can you explain why? In case somebody didn't understand what I meant by the sorting order, I meant that shortest length strings are sorted first AND if one or more strings are of same length then they are sorted using < operator. Thanks!

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• Pointing to vectors

  - by Matt Munson

  #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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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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• Question regarding built-in type variable is returned from a function

  - by Chan

  Hello, If a local object is returned in a function call, it has to do at least three steps: 1. Copy constructor is called to hold a copy. 2. Destroy local object. 3. A copy is return. For example: x = y + z If x is an integer object. A copy of y + z should be returned, then a new object is created, then assignment operator of x will take this object as parameter. So my question is: Is the same process used for built-in type such as int, double...? If they're not the same, how's it done? Thanks, Chan

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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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• 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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• 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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• 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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• Postgres column casting...

  - by Simon

  I have a query SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = 7 which doesn't work and throws ERROR: operator does not exist: character varying = integer LINE 4: FROM sq_ast WHERE assetid = 7 I can get it to work by doing SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = '7' Please note the quoting of the 7 in the WHERE clause... I am deploying an huge application and I cannot rewrite the core... similarly I don't want to risk changing the type of the column... I'm no Postgres expert... please help... Is there an option for strict casting of columns???

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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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• 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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• 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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• Trying to put a generic MyObj<T, U> into an IList where U can be different between objects

  - by Sergio Romero

  I have the following class definition: public interface IItem{} public class FirstObject<T, U> : IItem { public U SomeProperty { get; private set; } } IList<IItem> myList = new List<IItem>(); I did it like this because U can be of different types. Now I want to iterate the list and get my items back, the problem is that I do not know how to cast them back to their original type so I can read the value of SomeProperty. Thanks for your help.

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