null

What is a NULL value

I am wondering , what exactly is stored in the memory when we say a particular variable pointer to be NULL. suppose I have a structure, say typdef struct MEM_LIST MEM_INSTANCE; struct MEM_LIST { char *start_addr; int size; MEM_INSTANCE *next; }; MEM_INSTANCE *front; front = (MEM_INSTANCE*)malloc(sizeof(MEM_INSTANCE*))...

Is there a practical benefit to casting a NULL pointer to an object and calling one of its member functions?

Ok, so I know that technically this is undefined behavior, but nonetheless, I've seen this more than once in production code. And please correct me if I'm wrong, but I've also heard that some people use this "feature" as a somewhat legitimate substitute for a lacking aspect of the current C++ standard, namely, the inability to obtain the...

Comparing two date ranges within the same table

I have a table with sales per store as follows: SQL> select * from sales; ID ID_STORE DATE TOTAL ---------- -------- ---------- ------------------------------- 1 1 2010-01-01 500.00 2 1 2010-01-02 185.00 3 1 2010-01-03 135.00 4 1 2009-01-01 165.00...

Can PCRE regex match a null character?

I have a text source with nulls in it and I need to pull them out along with my regex pattern. Can regex even match a null character? I only realized I had them when my pattern refused to match and when I pasted it into Notepad++ it showed all the null characters. ...

Is null a class in java?

According to, http://www.freshvanilla.org:8080/display/www/Java+Interview+Questions Under, Which class is the superclass of every class? null seems to be the answer. I found that new Object().getClass().getSuperClass() verifies the answer as correct. But can null be considered a class? I see all primitive data types are re...

NULL handling with subselect in Hibernate Criteria API

I'm constructing a Hibernate Criterion, using a subselect as follows DetachedCriteria subselect = DetachedCriteria.forClass(NhmCode.class, "sub"); // the subselect selecting the maximum 'validFrom' subselect.add(Restrictions.le("validFrom", new Date())); // it should be in the past (null needs handling here) subselect.add(Property.f...

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

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. How can I tell Wor...

When was the NULL macro not 0?

I vaguely remember reading about this a couple of years ago, but I can't find any reference on the net. Can you give me an example where the NULL macro didn't expand to 0? Edit for clarity: Today it expands to either ((void *)0), (0), or (0L). However, there were architectures long forgotten where this wasn't true, and NULL expanded to...

Can a conforming C implementation #define NULL to be something wacky

I'm asking because of the discussion that's been provoked in this thread. Trying to have a serious back-and-forth discussion using comments under other people's replies is not easy or fun. So I'd like to hear what our C experts think without being restricted to 500 characters at a time. The C standard has precious few words to say a...

How to check if my string is equal to null?

I want to perform some action ONLY IF my string has a meaningful value. So, I tried this. if (!myString.equals("")) { doSomething } and this if (!myString.equals(null)) { doSomething } and this if ( (!myString.equals("")) && (!myString.equals(null))) { doSomething } and this if ( (!myString.equals("")) && (myString!=null)) { do...

Bizarre WHERE col = NULL behavior

This is a problem one of our developers brought to me. He stumbled across an old stored procedure which used 'WHERE col = NULL' several times. When the stored procedure is executed it returns data. If the query inside the stored procedure is executed manually it will not return data unless the 'WHERE col = NULL' references are changed t...

How can a not null constraint be dropped?

Let's say there's a table created as follows: create table testTable ( colA int not null ) How would you drop the not null constraint? I'm looking for something along the lines of ALTER TABLE testTable ALTER COLUMN colA DROP NOT NULL; which is what it would look like if I used PostgreSQL. To my amazement, as far as I've been able t...

Why does null need an explicit type cast here?

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 do we have to cast the null into an int? and why can't we simply provide an explicit...

AS 3.0 reference problem

I am finding it hard to fugure out the reference system in AS 3.0. this is the code i have (i have trimmed it down in order to find the problem but to no avail) package rpflash.ui { import flash.display.Sprite; import flash.display.MovieClip; import flash.display.Stage; import nowplaying; import flash.text.TextField; public class RP...

C++ How do you set an array of pointers to null in an initialiser list like way?

I am aware you cannot use an initialiser list for an array. However I have heard of ways that you can set an array of pointers to NULL in a way that is similar to an initialiser list. I am not certain how this is done. I have heard that a pointer is set to NULL by default, though I do not know if this is guaranteed/ in the C++ standard...

How to assign a value of a property to a var ONLY if the object isn't null

In my code, is there a shorthand that I can use to assign a variable the value of a object's property ONLY if the object isn't null? string username = SomeUserObject.Username; // fails if null I know I can do a check like if(SomeUserObject != null) but I think I saw a shorthand for this kind of test. I tried: string username = S...

Null Pointer Exception on a 2D array (Java)

I have a class, "Tetris", in which one of the instance variables is "board". "board" is 2D array of Color objects. Upon the creation of a tetris object I call a method that sets the dimensions of board and then sets all of the Color objects to be the Default value, that is to say, Color.blue. public Tetris(int rows, int cols) { this.r...

Why does my token return NULL and how can I fix it?(c++)

I've created a program to get a string input from a user and parse it into tokens and move a robot according to the input. The program is supposed to recognize these inputs(where x is an integer): "forward x" "back x" "turn left x" "turn right x" and "stop". The program does what it's supposed to for all commands except for "stop". When ...

.NET: Allow NULLS in DB fields?

Hi there, I have the task of re-factoring an SQLServer DB.... A lot of the tables and columns "ALLOW NULLS", Is this good practice... I seem to remember the authour of CSLA.NET saying it was really bad practice to allow nulls in a DB... If this is the case, what are my alternatives? Remove all "ALLOW NULLS" from all columns.... and ...

NULL value when using NSDateFormatter after setting NSDate property via XML parsing

Hello, I am using the following code to try and display in a time in a table cell. TimeSlot *timeSlot = [timeSlots objectAtIndex:indexPath.row]; NSDateFormatter *timeFormat = [[NSDateFormatter alloc] init]; [timeFormat setDateFormat:@"HH:mm:ss"]; NSLog(@"Time: %@", timeSlot.time); NSDate *mydate = timeSlot.time; NSLog(@"Time: %@", myda...