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• Calling functions from different classes

  - by A Ron Hubbard Clevenger

  I'm writing a program and I'm supposed to check and see if a certain object is in the list before I call it. I set up the contains() method which is supposed to use the equals() method of the Comparable interface I implemented on my Golfer class but it doesn't seem to call it (I put print statements in to check). I can't seem to figure out whats wrong with the code, the ArrayUnsortedList class I'm using to go through the list even uses the correct toString() method I defined in my Golfer class but for some reason it won't use the equals() method I implemented. //From "GolfApp.java" public class GolfApp{ ListInterface <Golfer>golfers = new ArraySortedList<Golfer> (20); Golfer golfer; //..*snip*.. if(this.golfers.contains(new Golfer(name,score))) System.out.println("The list already contains this golfer"); else{ this.golfers.add(this.golfer = new Golfer(name,score)); System.out.println("This golfer is already on the list"); } //From "ArrayUnsortedList.java" protected void find(T target){ location = 0; found = false; while (location < numElements){ if (list[location].equals(target)) //Where I think the problem is { found = true; return; } else location++; } } public boolean contains(T element){ find(element); return found; } //From "Golfer.java" public class Golfer implements Comparable<Golfer>{ //..irrelavant code sniped..// public boolean equals(Golfer golfer) { String thisString = score + ":" + name; String otherString = golfer.getScore() + ":" + golfer.getName() ; System.out.println("Golfer.equals() has bee called"); return thisString.equalsIgnoreCase(otherString); } public String toString() { return (score + ":" + name); } My main problem seems to be getting the find function of the ArrayUnsortedList to call my equals function in the find() part of the List but I'm not exactly sure why, like I said when I have it printed out it works with the toString() method I implemented perfectly. I'm almost positive the problem has to do with the find() function in the ArraySortedList not calling my equals() method. I tried using some other functions that relied on the find() method and got the same results.

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• Strategies for invoking subclass methods on generic objects

  - by Brad Patton

  I've run into this issue in a number of places and have solved it a bunch of different ways but looking for other solutions or opinions on how to address. The scenario is when you have a collection of objects all based off of the same superclass but you want to perform certain actions based only on instances of some of the subclasses. One contrived example of this might be an HTML document made up of elements. You could have a superclass named HTMLELement and subclasses of Headings, Paragraphs, Images, Comments, etc. To invoke a common action across all of the objects you declare a virtual method in the superclass and specific implementations in all of the subclasses. So to render the document you could loop all of the different objects in the document and call a common Render() method on each instance. It's the case where again using the same generic objects in the collection I want to perform different actions for instances of specific subclass (or set of subclasses). For example (an remember this is just an example) when iterating over the collection, elements with external links need to be downloaded (e.g. JS, CSS, images) and some might require additional parsing (JS, CSS). What's the best way to handle those special cases. Some of the strategies I've used or seen used include: Virtual methods in the base class. So in the base class you have a virtual LoadExternalContent() method that does nothing and then override it in the specific subclasses that need to implement it. The benefit being that in the calling code there is no object testing you send the same message to each object and let most of them ignore it. Two downsides that I can think of. First it can make the base class very cluttered with methods that have nothing to do with most of the hierarchy. Second it assumes all of the work can be done in the called method and doesn't handle the case where there might be additional context specific actions in the calling code (i.e. you want to do something in the UI and not the model). Have methods on the class to uniquely identify the objects. This could include methods like ClassName() which return a string with the class name or other return values like enums or booleans (IsImage()). The benefit is that the calling code can use if or switch statements to filter objects to perform class specific actions. The downside is that for every new class you need to implement these methods and can look cluttered. Also performance could be less than some of the other options. Use language features to identify objects. This includes reflection and language operators to identify the objects. For example in C# there is the is operator that returns true if the instance matches the specified class. The benefit is no additional code to implement in your object hierarchy. The only downside seems to be the lack of using something like a switch statement and the fact that your calling code is a little more cluttered. Are there other strategies I am missing? Thoughts on best approaches?

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• C++ linked list based tree structure. Sanely copy nodes between lists.

  - by krunk

  edit Clafification: The intention is not to remove the node from the original list. But to create an identical node (data and children wise) to the original and insert that into the new list. In other words, a "move" does not imply a "remove" from the original. endedit The requirements: Each Node in the list must contain a reference to its previous sibling Each Node in the list must contain a reference to its next sibling Each Node may have a list of child nodes Each child Node must have a reference to its parent node Basically what we have is a tree structure of arbitrary depth and length. Something like: -root(NULL) --Node1 ----ChildNode1 ------ChildOfChild --------AnotherChild ----ChildNode2 --Node2 ----ChildNode1 ------ChildOfChild ----ChildNode2 ------ChildOfChild --Node3 ----ChildNode1 ----ChildNode2 Given any individual node, you need to be able to either traverse its siblings. the children, or up the tree to the root node. A Node ends up looking something like this: class Node { Node* previoius; Node* next; Node* child; Node* parent; } I have a container class that stores these and provides STL iterators. It performs your typical linked list accessors. So insertAfter looks like: void insertAfter(Node* after, Node* newNode) { Node* next = after->next; after->next = newNode; newNode->previous = after; next->previous = newNode; newNode->next = next; newNode->parent = after->parent; } That's the setup, now for the question. How would one move a node (and its children etc) to another list without leaving the previous list dangling? For example, if Node* myNode exists in ListOne and I want to append it to listTwo. Using pointers, listOne is left with a hole in its list since the next and previous pointers are changed. One solution is pass by value of the appended Node. So our insertAfter method would become: void insertAfter(Node* after, Node newNode); This seems like an awkward syntax. Another option is doing the copying internally, so you'd have: void insertAfter(Node* after, const Node* newNode) { Node *new_node = new Node(*newNode); Node* next = after->next; after->next = new_node; new_node->previous = after; next->previous = new_node; new_node->next = next; new_node->parent = after->parent; } Finally, you might create a moveNode method for moving and prevent raw insertion or appending of a node that already has been assigned siblings and parents. // default pointer value is 0 in constructor and a operator bool(..) // is defined for the Node bool isInList(const Node* node) const { return (node->previous || node->next || node->parent); } // then in insertAfter and friends if(isInList(newNode) // throw some error and bail I thought I'd toss this out there and see what folks came up with.

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• Why is my WCF RIA Services custom object deserializing with an extra list member?

  - by oasasaurus

  I have been developing a Silverlight WCF RIA Services application dealing with mock financial transactions. To more efficiently send summary data to the client without going overboard with serialized entities I have created a summary class that isn’t in my EDM, and figured out how to serialize and send it over the wire to the SL client using DataContract() and DataMember(). Everything seemed to be working out great, until I tried to bind controls to a list inside my custom object. The list seems to always get deserialized with an extra, almost empty entity in it that I don’t know how to get rid of. So, here are some of the pieces. First the relevant bits from the custom object class: <DataContract()> _ Public Class EconomicsSummary Public Sub New() RecentTransactions = New List(Of Transaction) TotalAccountHistory = New List(Of Transaction) End Sub Public Sub New(ByVal enUser As EntityUser) Me.UserId = enUser.UserId Me.UserName = enUser.UserName Me.Accounts = enUser.Accounts Me.Jobs = enUser.Jobs RecentTransactions = New List(Of Transaction) TotalAccountHistory = New List(Of Transaction) End Sub <DataMember()> _ <Key()> _ Public Property UserId As System.Guid <DataMember()> _ Public Property NumTransactions As Integer <DataMember()> _ <Include()> _ <Association("Summary_RecentTransactions", "UserId", "User_UserId")> _ Public Property RecentTransactions As List(Of Transaction) <DataMember()> _ <Include()> _ <Association("Summary_TotalAccountHistory", "UserId", "User_UserId")> _ Public Property TotalAccountHistory As List(Of Transaction) End Class Next, the relevant parts of the function called to return the object: Public Function GetEconomicsSummary(ByVal guidUserId As System.Guid) As EconomicsSummary Dim objOutput As New EconomicsSummary(enUser) For Each objTransaction As Transaction In (From t As Transaction In Me.ObjectContext.Transactions.Include("Account") Where t.Account.aspnet_User_UserId = guidUserId Select t Order By t.TransactionDate Descending Take 10) objTransaction.User_UserId = objOutput.UserId objOutput.RecentTransactions.Add(objTransaction) Next objOutput.NumTransactions = objOutput.RecentTransactions.Count … Return objOutput End Function Notice that I’m collecting the NumTransactions count before serialization. Should be 10 right? It is – BEFORE serialization. The DataGrid is bound to the data source as follows: <sdk:DataGrid AutoGenerateColumns="False" Height="100" MaxWidth="{Binding ElementName=aciSummary, Path=ActualWidth}" ItemsSource="{Binding Source={StaticResource EconomicsSummaryRecentTransactionsViewSource}, Mode=OneWay}" Name="gridRecentTransactions" RowDetailsVisibilityMode="VisibleWhenSelected" IsReadOnly="True"> <sdk:DataGrid.Columns> <sdk:DataGridTextColumn x:Name="TransactionDateColumn" Binding="{Binding Path=TransactionDate, StringFormat=\{0:d\}}" Header="Date" Width="SizeToHeader" /> <sdk:DataGridTextColumn x:Name="AccountNameColumn" Binding="{Binding Path=Account.Title}" Header="Account" Width="SizeToCells" /> <sdk:DataGridTextColumn x:Name="CurrencyAmountColumn" Binding="{Binding Path=CurrencyAmount, StringFormat=\{0:c\}}" Header="Amount" Width="SizeToHeader" /> <sdk:DataGridTextColumn x:Name="TitleColumn" Binding="{Binding Path=Title}" Header="Description" Width="SizeToCells" /> <sdk:DataGridTextColumn x:Name="ItemQuantityColumn" Binding="{Binding Path=ItemQuantity}" Header="Qty" Width="SizeToHeader" /> </sdk:DataGrid.Columns> </sdk:DataGrid> You might be wondering where the ItemsSource is coming from, that looks like this: <CollectionViewSource x:Key="EconomicsSummaryRecentTransactionsViewSource" Source="{Binding Path=DataView.RecentTransactions, ElementName=EconomicsSummaryDomainDataSource}" /> When I noticed that the DataGrid had the extra row I tried outputting some data after the data source finishes loading, as follows: Private Sub EconomicsSummaryDomainDataSource_LoadedData(ByVal sender As System.Object, ByVal e As System.Windows.Controls.LoadedDataEventArgs) Handles EconomicsSummaryDomainDataSource.LoadedData If e.HasError Then System.Windows.MessageBox.Show(e.Error.ToString, "Load Error", System.Windows.MessageBoxButton.OK) e.MarkErrorAsHandled() End If Dim objSummary As EconomicsSummary = CType(EconomicsSummaryDomainDataSource.Data(0), EconomicsSummary) Dim sb As New StringBuilder("") sb.AppendLine(String.Format("Num Transactions: {0} ({1})", objSummary.RecentTransactions.Count.ToString(), objSummary.NumTransactions.ToString())) For Each objTransaction As Transaction In objSummary.RecentTransactions sb.AppendLine(String.Format("Recent TransactionId {0} dated {1} CurrencyAmount {2} NewBalance {3}", objTransaction.TransactionId.ToString, objTransaction.TransactionDate.ToString("d"), objTransaction.CurrencyAmount.ToString("c"), objTransaction.NewBalance.ToString("c"))) Next txtDebug.Text = sb.ToString() End Sub Output from that looks like this: Num Transactions: 11 (10) Recent TransactionId 2283 dated 6/1/2010 CurrencyAmount $31.00 NewBalance $392.00 Recent TransactionId 2281 dated 5/31/2010 CurrencyAmount $33.00 NewBalance $361.00 Recent TransactionId 2279 dated 5/28/2010 CurrencyAmount $8.00 NewBalance $328.00 Recent TransactionId 2277 dated 5/26/2010 CurrencyAmount $22.00 NewBalance $320.00 Recent TransactionId 2275 dated 5/24/2010 CurrencyAmount $5.00 NewBalance $298.00 Recent TransactionId 2273 dated 5/21/2010 CurrencyAmount $19.00 NewBalance $293.00 Recent TransactionId 2271 dated 5/20/2010 CurrencyAmount $20.00 NewBalance $274.00 Recent TransactionId 2269 dated 5/19/2010 CurrencyAmount $48.00 NewBalance $254.00 Recent TransactionId 2267 dated 5/18/2010 CurrencyAmount $42.00 NewBalance $206.00 Recent TransactionId 2265 dated 5/14/2010 CurrencyAmount $5.00 NewBalance $164.00 Recent TransactionId 0 dated 6/1/2010 CurrencyAmount $0.00 NewBalance $361.00 So I have a few different questions: -First and foremost, where the devil is that extra Transaction entity coming from and how do I get rid of it? Does it have anything to do with the other list of Transaction entities being serialized as part of the EconomicsSummary class (TotalAccountHistory)? Do I need to decorate the EconomicsSummary class members a little more/differently? -Second, where are the peculiar values coming from on that extra entity? PRE-POSTING UPDATE 1: I did a little checking, it looks like that last entry is the first one in the TotalAccountHistory list. Do I need to do something with CollectionDataContract()? PRE-POSTING UPDATE 2: I fixed one bug in TotalAccountHistory, since the objects weren’t coming from the database their keys weren’t unique. So I set the keys on the Transaction entities inside TotalAccountHistory to be unique and guess what? Now, after deserialization RecentTransactions contains all its original items, plus every item in TotalAccountHistory. I’m pretty sure this has to do with the deserializer getting confused by two collections of the same type. But I don’t yet know how to resolve it…

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• Is there a way to circumvent Python list.append() becoming progressively slower in a loop as the lis

  - by Deniz

  I have a big file I'm reading from, and convert every few lines to an instance of an Object. Since I'm looping through the file, I stash the instance to a list using list.append(instance), and then continue looping. This is a file that's around ~100MB so it isn't too large, but as the list grows larger, the looping slows down progressively. (I print the time for each lap in the loop). This is not intrinsic to the loop ~ when I print every new instance as I loop through the file, the program progresses at constant speed ~ it is only when I append them to a list it gets slow. My friend suggested disabling garbage collection before the while loop and enabling it afterward & making a garbage collection call. Did anyone else observe a similar problem with list.append getting slower? Is there any other way to circumvent this?

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• Convert a generic list to an array

  - by Freewind

  I have searched for this, but unfortunately, I don't get the correct answer. class Helper { public static <T> T[] toArray(List<T> list) { T[] array = (T[]) new Object[list.size()]; for (int i = 0; i < list.size(); i++) { array[i] = list.get(i); } return array; } } Test it: public static void main(String[] args) { List<String> list = new ArrayList<String>(); list.add("abc"); String[] array = toArray(list); System.out.println(array); } But there is an error thrown: Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String; at test.Helper.main(Helper.java:30) How to solve this?

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• I am confused -- Will this code always work?

  - by Shekhar

  Hello, I have written this piece of code public class Test{ public static void main(String[] args) { List<Integer> list = new ArrayList<Integer>(); for(int i = 1;i<= 4;i++){ new Thread(new TestTask(i, list)).start(); } while(list.size() != 4){ // this while loop required so that all threads complete their work } System.out.println("List "+list); } } class TestTask implements Runnable{ private int sequence; private List<Integer> list; public TestTask(int sequence, List<Integer> list) { this.sequence = sequence; this.list = list; } @Override public void run() { list.add(sequence); } } This code works and prints all the four elements of list on my machine. My question is that will this code always work. I think there might be a issue in this code when two/or more threads add element to this list at the same point. In that case it while loop will never end and code will fail. Can anybody suggest a better way to do this? I am not very good at multithreading and don't know which concurrent collection i can use? Thanks Shekhar

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• VB.net: Is my Thread Safe List Solution actually safe?

  - by Shiftbit

  I've added teh following Extensions to my Project in order to create a thread safe list: Extensions If I want to conduct a simple operation on my list <Extension()> _ Public Sub Action(Of T)(ByVal list As List(Of T), ByVal action As Action(Of List(Of T))) SyncLock (list) action(list) End SyncLock End Sub If I want to pass it more than one parameter I could simply extend it with more items... <Extension()> _ Public Sub Action(Of T)(ByVal list As List(Of T), ByVal action As Action(Of List(Of T), T), ByVal item As T) SyncLock (list) Action(list, item) End SyncLock End Sub Actions I have created the following Action Examples: Private Sub Read(Of T)(ByVal list As List(Of T)) Console.WriteLine("Read") For Each item As T In list Console.WriteLine(item.ToString) Thread.Sleep(10) Next End Sub and also one that takes a parameter: Private Sub Write(Of T)(ByVal list As List(Of T), ByVal item As T) Thread.Sleep(100) list.Add(item) Console.WriteLine("Write") End Sub Initiating Then in my various threads I will call my Actions with: list.Action(AddressOf Read) or list.Action(AddressOf Write2, 10) Are these Extenxion methods thread safe or do you have other recommendations?

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• Embedding generic sql queries into c# program

  - by Pooja Balkundi

  Okay referring to my first question code in the main, I want the user to enter employee name at runtime and then i take this name which user has entered and compare it with the e_name of my emp table , if it exists i want to display all information of that employee , how can I achieve this ? using System; using System.Collections.Generic; using System.Linq; using System.Windows.Forms; using MySql.Data.MySqlClient; namespace ConnectCsharppToMySQL { public class DBConnect { private MySqlConnection connection; private string server; private string database; private string uid; private string password; string name; //Constructor public DBConnect() { Initialize(); } //Initialize values private void Initialize() { server = "localhost"; database = "test"; uid = "root"; password = ""; string connectionString; connectionString = "SERVER=" + server + ";" + "DATABASE=" + database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";"; connection = new MySqlConnection(connectionString); } //open connection to database private bool OpenConnection() { try { connection.Open(); return true; } catch (MySqlException ex) { //When handling errors, you can your application's response based //on the error number. //The two most common error numbers when connecting are as follows: //0: Cannot connect to server. //1045: Invalid user name and/or password. switch (ex.Number) { case 0: MessageBox.Show("Cannot connect to server. Contact administrator"); break; case 1045: MessageBox.Show("Invalid username/password, please try again"); break; } return false; } } //Close connection private bool CloseConnection() { try { connection.Close(); return true; } catch (MySqlException ex) { MessageBox.Show(ex.Message); return false; } } //Insert statement public void Insert() { string query = "INSERT INTO emp (e_name, age) VALUES('Pooja R', '21')"; //open connection if (this.OpenConnection() == true) { //create command and assign the query and connection from the constructor MySqlCommand cmd = new MySqlCommand(query, connection); //Execute command cmd.ExecuteNonQuery(); //close connection this.CloseConnection(); } } //Update statement public void Update() { string query = "UPDATE emp SET e_name='Peachy', age='22' WHERE e_name='Pooja R'"; //Open connection if (this.OpenConnection() == true) { //create mysql command MySqlCommand cmd = new MySqlCommand(); //Assign the query using CommandText cmd.CommandText = query; //Assign the connection using Connection cmd.Connection = connection; //Execute query cmd.ExecuteNonQuery(); //close connection this.CloseConnection(); } } //Select statement public List<string>[] Select() { string query = "SELECT * FROM emp where e_name=(/*I WANT USER ENTERED NAME TO GET INSERTED HERE*/)"; //Create a list to store the result List<string>[] list = new List<string>[3]; list[0] = new List<string>(); list[1] = new List<string>(); list[2] = new List<string>(); //Open connection if (this.OpenConnection() == true) { //Create Command MySqlCommand cmd = new MySqlCommand(query, connection); //Create a data reader and Execute the command MySqlDataReader dataReader = cmd.ExecuteReader(); //Read the data and store them in the list while (dataReader.Read()) { list[0].Add(dataReader["e_id"] + ""); list[1].Add(dataReader["e_name"] + ""); list[2].Add(dataReader["age"] + ""); } //close Data Reader dataReader.Close(); //close Connection this.CloseConnection(); //return list to be displayed return list; } else { return list; } } public static void Main(String[] args) { DBConnect db1 = new DBConnect(); Console.WriteLine("Initializing"); db1.Initialize(); Console.WriteLine("Search :"); Console.WriteLine("Enter the employee name"); db1.name = Console.ReadLine(); db1.Select(); Console.ReadLine(); } } }

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• Why doesn't this list comprehension do what I expect it to do?

  - by Az

  The original list project_keys = sorted(projects.keys()) is [101, 102, 103, 104, 105, 106, 107, 108, 109, 110] where the following projects were deemed invalid this year: 108, 109, 110. Thus: for project in projects.itervalues(): # The projects dictionary is mapped to the Project class if project.invalid: # Where invalid is a Bool parameter in the Project class project_keys.remove(project.proj_id) print project_keys This will return a list of integers (which are project id's) as such: [101, 102, 103, 104, 105, 106, 107] Sweet. Now, I wanted it try the same thing using a list comprehension. project_keys = [project_keys.remove(project.proj_id) for project in projects.itervalues() if project.invalid print project_keys This returns: [None, None, None] So I'm populating a list with the same number as the removed elements but they're Nones? Can someone point out what I'm doing wrong? Additionally, why would I use a list comprehension over the for-if block at the top? Conciseness? Looks nicer?

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• trying to prune down a list of files

  - by romunov

  I have a list of files and I'm trying to extract all layer1_*.grd files. Is there a way of doing this in one grep expression? lof <- c("layer1_1.grd", "layer1_1.gri", "layer1_2.grd", "layer1_2.gri", "layer1_3.grd", "layer1_3.gri", "layer1_4.grd", "layer1_4.gri", "layer1_5.grd", "layer1_5.gri", "layer2_1.grd", "layer2_1.gri", "layer2_2.grd", "layer2_2.gri", "layer2_3.grd", "layer2_3.gri", "layer2_4.grd", "layer2_4.gri", "layer2_5.grd", "layer2_5.gri", "layer3_1.grd", "layer3_1.gri", "layer3_2.grd", "layer3_2.gri", "layer3_3.grd", "layer3_3.gri", "layer3_4.grd", "layer3_4.gri", "layer3_5.grd", "layer3_5.gri", "layer4_1.grd", "layer4_1.gri", "layer4_2.grd", "layer4_2.gri", "layer4_3.grd", "layer4_3.gri", "layer4_4.grd", "layer4_4.gri", "layer4_5.grd", "layer4_5.gri" I tried doing this in two steps: list.of.files <- list.files(pattern = c("1_")) list.of.files <- list.of.files[grep(".grd", list.of.files)] Can someone enlighten me how to do this with grep in one step? I naively tried passing list() and c() to the grep but, as you can imagine, it doesn't work. list.of.files <- list.files() list.of.files <- list.of.files[grep(list("1_", ".grd"), list.of.files)]

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• In C#: How to declare a generic Dictionary with a type as key and an enumeration of that type as val

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: (Edited to follow johny g's comment) private IDictionary<Type, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• C++, generic programming and virtual functions. How do I get what I want?

  - by carleeto

  This is what I would like to do using templates: struct op1 { virtual void Method1() = 0; } ... struct opN { virtual void MethodN() = 0; } struct test : op1, op2, op3, op4 { virtual void Method1(){/*do work1*/}; virtual void Method2(){/*do work2*/}; virtual void Method3(){/*do work3*/}; virtual void Method4(){/*do work4*/}; } I would like to have a class that simply derives from a template class that provides these method declarations while at the same time making them virtual. This is what I've managed to come up with: #include <iostream> template< size_t N > struct ops : ops< N - 1 > { protected: virtual void DoStuff(){ std::cout<<N<<std::endl; }; public: template< size_t i > void Method() { if( i < N ) ops<i>::DoStuff(); } //leaving out compile time asserts for brevity } struct test : ops<6> { }; int main( int argc, char ** argv ) { test obj; obj.Method<3>(); //prints 3 return 0; } However, as you've probably guessed, I am unable to override any of the 6 methods I have inherited. I'm obviously missing something here. What is my error? No, this isn't homework. This is curiosity.

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• How do I convert a Python list of lists of lists into a C array by using ctypes?

  - by pc05

  As seen here How do I convert a Python list into a C array by using ctypes? this code will take a python array and transform it to a C array. import ctypes arr = (ctypes.c_int * len(pyarr))(*pyarr) Which would the way of doing the same with a list of lists or a lists of lists of lists? For example, for the following variable list3d = [[[40.0, 1.2, 6.0, 0.3], [50.0, 4.2, 0, 0]], [[40.0, 1.2, 6.0, 0.3], [50.0, 4.2, 0, 0]], [[40.0, 1.2, 6.0, 0.3], [50.0, 4.2, 0, 0]]] I have tried the following with no luck: ([[ctypes.c_double * 4] *2]*3)(*list3d) # *** TypeError: 'list' object is not callable (ctypes.c_double * 4 *2 *3)(*list3d) # *** TypeError: expected c_double_Array_4_Array_2 instance, got list Thank you! EDIT: Just to clarify, I am trying to get one object that contains the whole multidimensional array, not a list of objects. This object's reference will be an input to a C DLL that expects a 3D array.

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• In C#: How to declare a generic Dictionary whose key and value types have a common constraint type?

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: private IDictionary<T, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• SEO strategy for h1, h2, h3 tags for list of items

  - by Theo G

  On a page on my website page I have a list of ALL the products on my site. This list is growing rapidly and I am wondering how to manage it from an SEO point of view. I am shortly adding a title to this section and giving it an H1 tag. Currently the name of each product in this list is not h1,2,3,4 its just styled text. However I was looking to make these h2,3,4. Questions: Is the use of h2,3,4 on these list items bad form as they should be used for content rather than all links? I am thinking of limiting this main list to only 8 items and using h2 tags for each name. Do you this this will have a negative or possible affect over all. I may create a piece of script which counts the first 8 items on the list. These 8 will get the h2, and any after that will get h3 (all styled the same). If I do add h tags should I put just on the name of the product or the outside of the a tag, therefore collecting all info. Has anyone been in a similar situation as this, and if so did they really see any significant difference?

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• Get 100 highest numbers from an infinite list

  - by Sachin Shanbhag

  One of my friend was asked this interview question - "There is a constant flow of numbers coming in from some infinite list of numbers out of which you need to maintain a datastructure as to return the top 100 highest numbers at any given point of time. Assume all the numbers are whole numbers only." This is simple, you need to keep a sorted list in descending order and keep a track on lowest number in that list. If new number obtained is greater than that lowest number then you have to remove that lowest number and insert the new number in sorted list as required. Then question was extended - "Can you make sure that the Order for insertion should be O(1)? Is it possible?" As far as I knew, even if you add a new number to list and sort it again using any sort algorithm, it would by best be O(logn) for quicksort (I think). So my friend told it was not possible. But he was not convinced, he asked to maintain any other data structure rather than a list. I thought of balanced Binary tree, but even there you will not get the insertion with order of 1. So the same question I have too now. Wanted to know if there is any such data structure which can do insertion in Order of 1 for above problem or it is not possible at all.

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• Generate a Word document from list data

  - by PeterBrunone

  This came up on a discussion list lately, so I threw together some code to meet the need.  In short, a colleague needed to take the results of an InfoPath form survey and give them to the user in Word format.  The form data was already in a list item, so it was a simple matter of using the SharePoint API to get the list item, formatting the data appropriately, and using response headers to make the client machine treat the response as MS Word content.  The following rudimentary code can be run in an ASPX (or an assembly) in the 12 hive.  When you link to the page, send the list name and item ID in the querystring and use them to grab the appropriate data. // Clear the current response headers and set them up to look like a word doc.HttpContext.Current.Response.Clear();HttpContext.Current.Response.Charset ="";HttpContext.Current.Response.ContentType ="application/msword";string strFileName = "ThatWordFileYouWanted"+ ".doc";HttpContext.Current.Response.AddHeader("Content-Disposition", "inline;filename=" + strFileName);// Using the current site, get the List by name and then the Item by ID (from the URL).string myListName = HttpContext.Current.Request.Querystring["listName"];int myID = Convert.ToInt32(HttpContext.Current.Request.Querystring["itemID"]);SPSite oSite = SPContext.Current.Site;SPWeb oWeb = oSite.OpenWeb();SPList oList = oWeb.Lists["MyListName"];SPListItem oListItem = oList.Items.GetItemById(myID);// Build a string with the data -- format it with HTML if you like. StringBuilder strHTMLContent = newStringBuilder();// *// Here's where you pull individual fields out of the list item.// *// Once everything is ready, spit it out to the client machine.HttpContext.Current.Response.Write(strHTMLContent);HttpContext.Current.Response.End();HttpContext.Current.Response.Flush();

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• General List of Common Programming Errors

  - by javamonkey79

  As one journey's from apprentice to journeyman to master I've noticed that one accumulates a list of best practices for things they've been bitten by. Personally, I write most of my stuff in java & SQL so my list tends to be slated towards them. I've accumulated the following: When doing list removal, always reverse iterate Avoid adding items to a list you are currently iterating on Watch out for NullPointerExceptions Now, I know there are language specific "common errors" links out there like this one. And I'm also aware of the pragmatic programmer tips, Martin Fowler's "code smells". Does anyone know of any good lists out there of things like I've listed above (re: list removal, adding items, etc). My guess is that there are some good QA folks out there that can probably throw me a bone here. I'm not looking for things the compiler can catch - I'm looking for common things that cause bugs. In the event that there isn't a list out there already then I welcome posting your own findings here. Thanks in advance!

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• Use of list-unsubscribe to improve inbox delivery

  - by Jeffrey Simon

  To overcome email being classified as spam by Gmail, Google recommends a number of steps, which we have implemented (namely SPF, DKIM, and Precedence: bulk). One additional measure they recommend at https://support.google.com/mail/bin/answer.py?hl=en&answer=81126#authentication reads as follows: Because Gmail can help users automatically unsubscribe from your email, we strongly recommend the following: Provide a 'List-Unsubscribe' header which points to an email address where the user can unsubscribe easily from future mailings (Note: This is not a substitute method for unsubscribing). Documentation for List-Unsubscribe is found at http://www.list-unsubscribe.com/. From this documentation I expect a button to be provided by a supported mail client. I have tested the 'List-Unsubscribe' header and it does not appear to provide the button. I have tested in both Gmail and OS X Mail. I tested with an http address and with both an email address and an http address. The format of the header is as follows: List-Unsubscribe: <mailto:[email protected]>, <http://domain.com/member/unsubscribe/[email protected]?id=12345N> No button appears in any test. My questions: How widely is List-Unsubscribe supported? Should a button be appearing somewhere, or does something else have to be present? I have seen a comment that even if the button is not present, services like Gmail, Yahoo, Hotmail/Windows Live would give higher regard to email having the header. Thus it might be worthwhile for this aspect alone. Please note that our standard email footer already contacts instructions and a link to allow unsubscribing from our email. Finally, is it worth while to implement this header? (That is, any downsides?)

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• List has no value after adding values in

  - by Sigh-AniDe

  I am creating a a ghost sprite that will mimic the main sprite after 10 seconds of the game. I am storing the users movements in a List<string> and i am using a foreach loop to run the movements. The problem is when i run through the game by adding breakpoints the movements are being added to the List<string> but when the foreach runs it shows that the list has nothing in it. Why does it do that? How can i fix it? this is what i have: public List<string> ghostMovements = new List<string>(); public void UpdateGhost(float scalingFactor, int[,] map) { // At this foreach, ghostMovements has nothing in it foreach (string s in ghostMovements) { // current position of the ghost on the tiles int mapX = (int)(ghostPostition.X / scalingFactor); int mapY = (int)(ghostPostition.Y / scalingFactor); if (s == "left") { switch (ghostDirection) { case ghostFacingUp: angle = 1.6f; ghostDirection = ghostFacingRight; Program.form.direction = ""; break; case ghostFacingRight: angle = 3.15f; ghostDirection = ghostFacingDown; Program.form.direction = ""; break; case ghostFacingDown: angle = -1.6f; ghostDirection = ghostFacingLeft; Program.form.direction = ""; break; case ghostFacingLeft: angle = 0.0f; ghostDirection = ghostFacingUp; Program.form.direction = ""; break; } } } } // The movement is captured here and added to the list public void captureMovement() { ghostMovements.Add(Program.form.direction); }

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• Re-order list in Python to ensure it starts with check values.

  - by S_Swede

  Dear all, I'm reading in serial data using Pyserial, to populate a list of 17 values (1byte each) at a sampling rate of 256Hz. The bytes I ultimately want to use are the 5th to 8th in the list. Providing no bytes are dropped, the first two values of the stream are always the same ('165','90'). I'm getting quite a few dropped values though, and my list values are shifting, so when I read the 5th-8th bytes, they aren't the correct values. I've partially combatted this by ensuring that before the wanted segement is captured, the first few values are checked against what they should be (i.e. if mylist[0]==165 &....). This is crude but ok since the chances of these two values appearing adjacent to each other in the list elsewhere is small. The problem is that this means as soon as the bytes shift, I'm losing a load of values, until it eventually realigns. My question is: what code can I use to either: a) Force the list to realign once it has been detected that it no longer starts with 165,90. (elif....). b) Detect where '165' & '90' are (next to each other) in the list and extract the values I want in relation to their position (next but one, onwards). Thanks in advance S_S Just noticed from the related Qs that I could use mylist.append(mylist.pop(0)) multiple times until they are in the right place. Is there a better way that anyone can suggest?

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• C#: Get key and value types of non-generic IDictionary at runtime

  - by Yang Zou

  there. I am wondering how I can get the key and value types of a non-generic IDictionary at runtime. For generic IDictionary, we can use reflection to get the generic arguments, which has been answered here. But for non-generic IDictionary, for instance, HybridDictionary, how can I get the key and value types? Thanks. Edit: I may not describe my problem properly. For non-generic IDictionary, if I have HyBridDictionary, which is declared as HyBridDictionary dict = new HyBridDictionary(); dict.Add("foo" , 1); dict.Add("bar", 2); How can I find out the type of the key is string and type of the value is int? Did I make the question clear? Thanks.

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• Implementing a generic repository for WCF data services

  - by cibrax

  The repository implementation I am going to discuss here is not exactly what someone would call repository in terms of DDD, but it is an abstraction layer that becomes handy at the moment of unit testing the code around this repository. In other words, you can easily create a mock to replace the real repository implementation. The WCF Data Services update for .NET 3.5 introduced a nice feature to support two way data bindings, which is very helpful for developing WPF or Silverlight based application but also for implementing the repository I am going to talk about. As part of this feature, the WCF Data Services Client library introduced a new collection DataServiceCollection<T> that implements INotifyPropertyChanged to notify the data context (DataServiceContext) about any change in the association links. This means that it is not longer necessary to manually set or remove the links in the data context when an item is added or removed from a collection. Before having this new collection, you basically used the following code to add a new item to a collection. Order order = new Order {   Name = "Foo" }; OrderItem item = new OrderItem {   Name = "bar",   UnitPrice = 10,   Qty = 1 }; var context = new OrderContext(); context.AddToOrders(order); context.AddToOrderItems(item); context.SetLink(item, "Order", order); context.SaveChanges(); Now, thanks to this new collection, everything is much simpler and similar to what you have in other ORMs like Entity Framework or L2S. Order order = new Order {   Name = "Foo" }; OrderItem item = new OrderItem {   Name = "bar",   UnitPrice = 10,   Qty = 1 }; order.Items.Add(item); var context = new OrderContext(); context.AddToOrders(order); context.SaveChanges(); In order to use this new feature, you first need to enable V2 in the data service, and then use some specific arguments in the datasvcutil tool (You can find more information about this new feature and how to use it in this post). DataSvcUtil /uri:"http://localhost:3655/MyDataService.svc/" /out:Reference.cs /dataservicecollection /version:2.0 Once you use those two arguments, the generated proxy classes will use DataServiceCollection<T> rather than a simple ObjectCollection<T>, which was the default collection in V1. There are some aspects that you need to know to use this feature correctly. 1. All the entities retrieved directly from the data context with a query track the changes and report those to the data context automatically. 2. A entity created with “new” does not track any change in the properties or associations. In order to enable change tracking in this entity, you need to do the following trick. public Order CreateOrder() {   var collection = new DataServiceCollection<Order>(this.context);   var order = new Order();   collection.Add(order);   return order; } You basically need to create a collection, and add the entity to that collection with the “Add” method to enable change tracking on that entity. 3. If you need to attach an existing entity (For example, if you created the entity with the “new” operator rather than retrieving it from the data context with a query) to a data context for tracking changes, you can use the “Load” method in the DataServiceCollection. var order = new Order {   Id = 1 }; var collection = new DataServiceCollection<Order>(this.context); collection.Load(order); In this case, the order with Id = 1 must exist on the data source exposed by the Data service. Otherwise, you will get an error because the entity did not exist. These cool extensions methods discussed by Stuart Leeks in this post to replace all the magic strings in the “Expand” operation with Expression Trees represent another feature I am going to use to implement this generic repository. Thanks to these extension methods, you could replace the following query with magic strings by a piece of code that only uses expressions. Magic strings, var customers = dataContext.Customers .Expand("Orders")         .Expand("Orders/Items") Expressions, var customers = dataContext.Customers .Expand(c => c.Orders.SubExpand(o => o.Items)) That query basically returns all the customers with their orders and order items. Ok, now that we have the automatic change tracking support and the expression support for explicitly loading entity associations, we are ready to create the repository. The interface for this repository looks like this,public interface IRepository { T Create<T>() where T : new(); void Update<T>(T entity); void Delete<T>(T entity); IQueryable<T> RetrieveAll<T>(params Expression<Func<T, object>>[] eagerProperties); IQueryable<T> Retrieve<T>(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] eagerProperties); void Attach<T>(T entity); void SaveChanges(); } The Retrieve and RetrieveAll methods are used to execute queries against the data service context. While both methods receive an array of expressions to load associations explicitly, only the Retrieve method receives a predicate representing the “where” clause. The following code represents the final implementation of this repository.public class DataServiceRepository: IRepository { ResourceRepositoryContext context; public DataServiceRepository() : this (new DataServiceContext()) { } public DataServiceRepository(DataServiceContext context) { this.context = context; } private static string ResolveEntitySet(Type type) { var entitySetAttribute = (EntitySetAttribute)type.GetCustomAttributes(typeof(EntitySetAttribute), true).FirstOrDefault(); if (entitySetAttribute != null) return entitySetAttribute.EntitySet; return null; } public T Create<T>() where T : new() { var collection = new DataServiceCollection<T>(this.context); var entity = new T(); collection.Add(entity); return entity; } public void Update<T>(T entity) { this.context.UpdateObject(entity); } public void Delete<T>(T entity) { this.context.DeleteObject(entity); } public void Attach<T>(T entity) { var collection = new DataServiceCollection<T>(this.context); collection.Load(entity); } public IQueryable<T> Retrieve<T>(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] eagerProperties) { var entitySet = ResolveEntitySet(typeof(T)); var query = context.CreateQuery<T>(entitySet); foreach (var e in eagerProperties) { query = query.Expand(e); } return query.Where(predicate); } public IQueryable<T> RetrieveAll<T>(params Expression<Func<T, object>>[] eagerProperties) { var entitySet = ResolveEntitySet(typeof(T)); var query = context.CreateQuery<T>(entitySet); foreach (var e in eagerProperties) { query = query.Expand(e); } return query; } public void SaveChanges() { this.context.SaveChanges(SaveChangesOptions.Batch); } } For instance, you can use the following code to retrieve customers with First name equal to “John”, and all their orders in a single call. repository.Retrieve<Customer>(    c => c.FirstName == “John”, //Where    c => c.Orders.SubExpand(o => o.Items)); In case, you want to have some pre-defined queries that you are going to use across several places, you can put them in an specific class. public static class CustomerQueries {   public static Expression<Func<Customer, bool>> LastNameEqualsTo(string lastName)   {     return c => c.LastName == lastName;   } } And then, use it with the repository. repository.Retrieve<Customer>(    CustomerQueries.LastNameEqualsTo("foo"),    c => c.Orders.SubExpand(o => o.Items));

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• after changing sources.list on ubuntu, how do I make him reload/refresh?

  - by Itay Moav

  after changing sources.list on ubuntu, how do I make him reload/refresh? So new packages in the new sources will be found?

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