What is the right way to check for a null string in Objective-C?

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I was using this in my iPhone app

if (title == nil) {
    // do something
}

but it throws some exception, and the console shows that the title is "(null)".

So I'm using this now:

if (title == nil || [title isKindOfClass:[NSNull class]]) {
    //do something
}

What is the difference, and what is the best way to determine whether a string is null?

As others have pointed out, there are many kinds of "null" under Cocoa/Objective C. But one further thing to note is that [title isKindOfClass:[NSNull class]] is pointlessly complex since [NSNull null] is documented to be a singleton so you can just check for pointer equality. See Topics for Cocoa: Using Null.

So a good test might be:

if (title == (id)[NSNull null] || title.length == 0 ) title = @"Something";

Note how you can use the fact that even if title is nil, title.length will return 0/nil/false, ie 0 in this case, so you do not have to special case it. This is something that people who are new to Objective C have trouble getting used to, especially coming form other languages where messages/method calls to nil crash.

How to test for a (null) string in Objective C, best way to determine whether a string is null? Answers: As others have pointed out, there are many kinds of “null” under Cocoa/Objective C. Handling nulls in C# the right way. first we have to check if the movie object is null, and if it is, return a not found. into another one (a string) we use

it is just as simple as

if([object length] >0)
{
  // do something
}

remember that in objective C if object is null it returns 0 as the value.

This will get you both a null string and a 0 length string.

What is the right way to check for a null string in Objective-C , I wanted to test if a string has a value when it's returned from Core Data. So I thought, the right way to do this was to see if it's equal to nothing,  You can quickly test for null or empty variables in a Bash shell script. You need to pass the -z or -n option to the test command or to the if command or use conditional expression. This page shows how to find out if a bash shell variable has NULL value or not using the test command. To find out if a bash variable is null:

How to test for a (null) string in Objective C, [code]if( theString == nil ) { /*. do something about having a null string */ } [/​code]But this is very unusual code - in Objective-C, checking for nil (null) isn't usually Computer Programming: What is the correct way to null an array in C? If there is an [NSNull null], you might get an exception but that is fine: Objective-C exceptions indicate programming errors. And you have a programming error that needs fixing by changing some code. If an object could be [NSNull null], then you check for this quite simply by testing (object == [NSNull null]).

Whats with all these "works for me answers" ? We're all coding in the same language and the rules are

  1. Ensure the reference isn't nil
  2. Check and make sure the length of the string isn't 0

That is what will work for all. If a given solution only "works for you", its only because your application flow won't allow for a scenario where the reference may be null or the string length to be 0. The proper way to do this is the method that will handle what you want in all cases.

How to check if NSString is null or not?, NSString iphone ios ios sdk NSString in IOS SDK test for empty string test for blank string Objective C check for blank string in ios check for blank string in  It checks it using a null check using != null and isEmpty () method of string. In plain terms, if a string isn't a null and isEmpty () returns false, it's not either null or empty. Else, it is. However, the above program doesn't return empty if a string contains only whitespace characters (spaces).

I have found that in order to really do it right you end up having to do something similar to

if ( ( ![myString isEqual:[NSNull null]] ) && ( [myString length] != 0 ) ) {
}

Otherwise you get weird situations where control will still bypass your check. I haven't come across one that makes it past the isEqual and length checks.

test if an NSString is empty in Objective C, I was using this in my iPhone app if (title == nil) { // do something }. but it throws some exception, and the console shows that the title is "(null)". So I'm using this  How to C# String Null How to handle null String in C#? A C# string is an array of characters declared using the string keyword. String objects are immutable, meaning that they cannot be changed once they have been created. What is C# null ? The null keyword is a special case for a variable value.

Google Objective-C Style Guide, Consistency with the way Apple SDKs use Objective-C has value for the GOOD​: #import "Shared/Util/Foo.h" @implementation Foo { /** The string Note too that this is distinct from checking C/C++ pointers and block pointers against NULL  String.concat() and Google Guava’s Joiner both throw a NullPointerException if any of the variables are null. Apache Commons’ StringUtils concatenates the empty string in place of null variables. The other concatenation methods concatenate “null” whenever there is a null variable.

nil / Nil / NULL / NSNull, In Objective-C, there are a few different varieties of nothing: NULL , nil , Nil , and NSNull . But in Objective-C, invoking a method on nil returns a zero value things for Objective-C developers, as it obviates the need to check for nil of an array, the terminating byte of a string, or the simply result of “2 - 2”. The null-coalescing operator ?? returns the value of its left-hand operand if it isn't null; otherwise, it evaluates the right-hand operand and returns its result. The ?? operator doesn't evaluate its right-hand operand if the left-hand operand evaluates to non-null. Available in C# 8.0 and later, the null-coalescing assignment operator

Nullability and Objective-C - Swift Blog, In previous Xcode releases, some Apple frameworks had been You can use _Nullable and _Nonnull almost anywhere you can use the normal C const keyword, nicer way to write these annotations: within method declarations you In particular, you can still check parameters marked nonnull to see if  A Better Way. Other languages like Groovy and C# have a nice null-conditional operator that allows the programmer to specify that a chain of references might contain a null somewhere along the way, and a natural way to deal with that is to just short-circuit the chain of calls and result in a null value.

Comments
  • Solution : jayprakashdubey.blogspot.in/2014/09/…
  • Thanks! However I asked this question in the first place because I was getting exception because the "title" null.
  • What type is title supposed to be? If it's an NSString, for instance, I receive the following warning: comparison of distinct Objective-C types 'struct NSNull *' and 'struct NSString *' lacks a cast Is there any way of removing this (I dunno if things have changed since this question was asked)?
  • Serves me right for posting code without compiling it ;-). title is presumably an NSString, but regardless of title's type, just cast null to the generic id type: (id)[NSNull null].
  • @PeterNLewis Hi, I tested a case by setting a string to nil and see if it passes this statement: if(string == (id)[NSNull null]). But it never passed. Can you cite a sample where string will be equal to [NSNull null]. ?
  • @JLT nil and [NSNull null] will never be the same. [NSNull null] is a singleton object that can be used as a stand in for nil when nil cannot be used (eg in an NSArray or NSDictionary value). So a use case might be where you had an NSArray of optional strings, some of which might be null, and you use [NSNull null] in the array for the null cases. In practice, the test is rarely needed, only when you (or a library you use!) actively use [NSNull null] as a placeholder.
  • This won't work if object is NSNull, still need to explicitly check that first.
  • you could also make a category for NSNull to make it return 0 to the length message :)
  • Yup, this'll crash if the object is NSNull.
  • This will crash if object is equal to NSNull
  • In addition to the NSNull unrecognized selector issue, this won't differentiate between a NSString pointer that is nil, or a NSString that is actually there but is essentially an empty string. (For example as a literal object = @""; or object = nil;)
  • Annoyingly I don't have enough "points" to add a second hyperlink (even to something on this site) see also: - stackoverflow.com/questions/598396/…
  • ...allow me. Although you should be able to edit your own posts from rep 0.
  • Thanks - that was very kind. When I wrote my initial post it said something like new users can only add 1 hyperlink (which seems a bit harsh - especially for cross links in this site).