null – Page 44 – Tarik Billa

In Objective-C why should I check if self = [super init] is not nil?

November 13, 2022 by Tarik

For example: [[NSData alloc] initWithContentsOfFile:@”this/path/doesn’t/exist/”]; [[NSImage alloc] initWithContentsOfFile:@”unsupportedFormat.sjt”]; [NSImage imageNamed:@”AnImageThatIsntInTheImageCache”]; … and so on. (Note: NSData might throw an exception if the file doesn’t exist). There are quite a few areas where returning nil is the expected behaviour when a problem occurs, and because of this it’s standard practice to check for nil pretty much … Read more

How to tell if a string is not defined in a Bash shell script

November 12, 2022 by Tarik

I think the answer you are after is implied (if not stated) by Vinko’s answer, though it is not spelled out simply. To distinguish whether VAR is set but empty or not set, you can use: if [ -z “${VAR+xxx}” ]; then echo “VAR is not set at all”; fi if [ -z “$VAR” ] … Read more

Why `null >= 0 && null

November 12, 2022 by Tarik

Your real question seem to be: Why: null >= 0; // true But: null == 0; // false What really happens is that the Greater-than-or-equal Operator (>=), performs type coercion (ToPrimitive), with a hint type of Number, actually all the relational operators have this behavior. null is treated in a special way by the Equals … Read more

What are the advantages of using nullptr?

October 26, 2022 by Tarik

In that code, there doesn’t seem to be an advantage. But consider the following overloaded functions: void f(char const *ptr); void f(int v); f(NULL); //which function will be called? Which function will be called? Of course, the intention here is to call f(char const *), but in reality f(int) will be called! That is a … Read more

Unique ways to use the null coalescing operator [closed]

October 25, 2022 by Tarik

Well, first of all, it’s much easier to chain than the standard ternary operator: string anybody = parm1 ?? localDefault ?? globalDefault; vs. string anyboby = (parm1 != null) ? parm1 : ((localDefault != null) ? localDefault : globalDefault); It also works well if a null-possible object isn’t a variable: string anybody = Parameters[“Name”] ?? … Read more

When should I use nil and NULL in Objective-C?

October 25, 2022 by Tarik

They differ in their types. They’re all zero, but NULL is a void *, nil is an id, and Nil is a Class pointer.

Why does NULL = NULL evaluate to false in SQL server

October 25, 2022 by Tarik

Think of the null as “unknown” in that case (or “does not exist”). In either of those cases, you can’t say that they are equal, because you don’t know the value of either of them. So, null=null evaluates to not true (false or null, depending on your system), because you don’t know the values to … Read more

How do I get SUM function in MySQL to return ‘0’ if no values are found?

October 24, 2022 by Tarik

Use COALESCE to avoid that outcome. SELECT COALESCE(SUM(column),0) FROM table WHERE … To see it in action, please see this sql fiddle: http://www.sqlfiddle.com/#!2/d1542/3/0 More Information: Given three tables (one with all numbers, one with all nulls, and one with a mixture): SQL Fiddle MySQL 5.5.32 Schema Setup: CREATE TABLE foo ( id INT NOT NULL … Read more

What is the correct way to represent null XML elements?

October 24, 2022 by Tarik

xsi:nil is the correct way to represent a value such that: When the DOM Level 2 call getElementValue() is issued, the NULL value is returned. xsi:nil is also used to indicate a valid element with no content even if that elements content type normally doesn’t allow empty elements. If an empty tag is used, getElementValue() … Read more

How to check null objects in jQuery

October 24, 2022 by Tarik

Check the jQuery FAQ… You can use the length property of the jQuery collection returned by your selector: if ( $(‘#myDiv’).length ){}