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• Pointer to struct, containing pointer to an object, for which I want to call a function

  - by user1795609

  So I've created an ADT which is a singly linked list made up of nodes. These Nodes each have a pointer to an object in them called data. Class Structure { struct Node { Object *data; Node *next; }; }; Node *head; I am trying to call a function in the object, like this: head = new Node; head -> data = new Object();…

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• Call a void* as a function without declaring a function pointer

  - by ToxIk

  I've searched but couldn't find any results (my terminology may be off) so forgive me if this has been asked before. I was wondering if there is an easy way to call a void* as a function in C without first declaring a function pointer and then assigning the function pointer the address; ie. assuming the function to be called is type void(void) …

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• Accessing subclass members from a superclass pointer C++

  - by Dr. Monkey

  I have an array of custom class Student objects. CourseStudent and ResearchStudent both inherit from Student, and all the instances of Student are one or the other of these. I have a function to go through the array, determine the subtype of each Student, then call subtype-specific member functions on them. The problem is, because these…

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• pointer to const member function typedef

  - by oldcig

  I know it's possible to separate to create a pointer to member function like this struct K { void func() {} }; typedef void FuncType(); typedef FuncType K::* MemFuncType; MemFuncType pF = &K::func; Is there similar way to construct a pointer to a const function? I've tried adding const in various places with no success. I've…

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• Can I catch bad pointer errors in C++?

  - by Simon

  Hi there, I was wondering if there is a possibility to catch errors like this in C++: object* p = new object; delete p; delete p; //this would cause an error, can I catch this? Can I check if the pointer is valid? Can I catch some exception? I know I could set the pointer p to NULL after the first object deletion. But just…

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• Member Function Pointer not quite right

  - by BlackDuck

  I have a SpecialisedRedBlackTree class that is templated. My Month class is not. In my Month class I have a private member which is an instance of SpecialisedRedBlackTree: SpecialisedRedBlackTree<Day> m_windSpeedTree; As you can see it will take the Day class/object (please correct me on any terms I get wrong). In my…

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• C and C++: Array element access pointer vs int

  - by begun

  Is there a performance difference if you either do myarray[ i ] or store the adress of myarray[ i ] in a pointer?

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• How can I optimize this subqueried and Joined MySQL Query?

  - by kevzettler

  I'm pretty green on mysql and I need some tips on cleaning up a query. It is used in several variations through out a site. Its got some subquerys derived tables and fun going on. Heres the query: # Query_time: 2 Lock_time: 0 Rows_sent: 0 Rows_examined: 0 SELECT * FROM ( SELECT products . *, categories.category_name AS…

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• Identifying and removing null characters in UNIX

  - by fahdshariff

  I have a text file containing unwanted null characters. When I try to view it in I see ^@ symbols, interleaved in normal text. How can I: a) Identify which lines in the file contains null characters? I have tried grepping for \0 and \x0, but this did not work. b) Remove the null characters? Running strings on the file…

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• Wordpress databse insert() and update() - using NULL values

  - by pygorex1

  Wordpress ships with the wpdb class which handles CRUD operations. The two methods of this class that I'm interested in are the insert() (the C in CRUD) and update() (the U in CRUD). A problem arises when I want to insert a NULL into a mysql database column - the wpdb class escapes PHP null variables to empty strings.…

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• Bus Timetable database design

  - by paddydub

  hi, I'm trying to design a db to store the timetable for 300 different bus routes, Each route has a different number of stops and different times for Monday-Friday, Saturday and Sunday. I've represented the bus departure times for each route as follows, I'm not sure if i should have null values in the table, does…

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• Why does null need to be casted?

  - by BlueRaja The Green Unicorn

  The following code does not compile: //int a = ... int? b = (int?) (a != 0 ? a : null); In order to compile, it needs to be changed to int? b = (a != 0 ? a : (int?) null); Since both b = null and b = a are legal, this doesn't make sense to me. Why does null need to be casted, and why can't we simply cast the…

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• LINQ-to-entities - Null reference

  - by BlueRaja

  I could swear this was working the other day: var resultSet = (from o in _entities.Table1 where o.Table2.Table3.SomeColumn == SomeProperty select o ).First(); SelectedItem = resultSet.Table2.SomeOtherColumn; I am getting a null reference exception on the last line: resultSet.Table2 is null. Not…

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• Compilers behave differently with a null parameter of a generic method

  - by Eyal Schneider

  The following code compiles perfectly with Eclipse, but fails to compile with javac: public class HowBizarre { public static <P extends Number, T extends P> void doIt(P value) { } public static void main(String[] args) { doIt(null); } } I simplified the code, so T is…

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• linq null parameter

  - by kusanagi

  how can i do the code static string BuildMenu(List<Menu> menu, int? parentId) { foreach (var item in menu.Where(i => i.ParentMenu == parentId || i.ParentMenu.MenuId == parentId).ToList()) { } } return BuildMenu(menuList,null); so if…

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• Identifying and removing null characters in UNIX

  - by fahdshariff

  I have a text file containing unwanted null characters. When I try to view it in I see ^@ symbols, interleaved in normal text. How can I: a) Identify which lines in the file contains null characters? I have tried grepping for \0 and \x0, but this did not work. b) Remove the null characters? Running…

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• How Oracle 10g evaluates NULL in boolean expressions

  - by Phani Kumar PV

  if not (i_ReLaunch = 1 and (dt_enddate is not null)) How this epression will be evaluated in Oracle 10g when the input value of the i_ReLaunch = null and the value of the dt_enddate is not null it is entering the loop. According to the rules in normal c# and all it should not enter the loop as …

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• MessageBroker.getMessageBroker(null) getting null pointer Exception

  - by Shital

  I am creating Dynamic Destinations MessageBroker broker = MessageBroker.getMessageBroker(null); MessageService service = (MessageService) broker.getService("message-service"); MessageDestination destination = (MessageDestination) service.createDestination("Group1"); if…

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• Alter Dilemma : How to use to set Primary and other attributes.

  - by Rachel

  I have following table in database AND I need to alter it to below mentioned schema. Initially I was drop the current database and creating new one using the create but I am not supposed to do that and use ALTER but am not sure as to how can I use ALTER to add primary key and other constraints.…

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• Checking instance of non-class constrained type parameter for null in generic method

  - by casperOne

  I currently have a generic method where I want to do some validation on the parameters before working on them. Specifically, if the instance of the type parameter T is a reference type, I want to check to see if it's null and throw an ArgumentNullException if it's null. Something along the…

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• What is null an instanceof?

  - by kunjaan

  Is null an instance of anything? What set does 'null' belong to? What is null? How is it represented in the memory?

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• R: preventing unlist to drop NULL values

  - by nico

  I'm running into a strange problem. I have a vector of lists and I use unlist on them. Some of the elements in the vectors are NULL and unlist seems to be dropping them. How can I prevent this? Here's a simple (non) working example showing this unwanted feature of unlist a = c(list("p1"=2,…

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• SSIS Script Component, Allow Null values

  - by user2471943

  I have a SSIS package that I am programming and my script component won't allow null column inputs. I have checked the box to keep nulls in the flat file source component. My program is running well until my script component where I get the error "The column has a null value" (super vague, I…

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• node to traverse cannot be null (Hibernate SQL)

  - by tiswas

  I'm performing a SQL query through hibernate, which looks like: SELECT thi FROM track_history_items thi JOIN artists art ON thi.artist_id = art.id WHERE thi.type = "TrackBroadcast" GROUP BY art.name ORDER thi.createdAt DESC but I'm getting the message that 'Node to traverse cannot…

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• To "null" or not to "null" my class's attributes

  - by Helper Method

  When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public…

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