How do I check if a string is null in Objective-C?
You can check if [string length] == 0 . This will check if it’s a valid but empty string (@””) as well as if it’s nil, since calling length on nil will also return 0. There are some very rare NSStrings where this will result in a false negative (saying the string isn’t empty, when, for practical purposes, it is).
What is null in Objective-C?
C represents nothing as 0 for primitive values and NULL for pointers (which is equivalent to 0 in a pointer context). The only time you see NULL in Objective-C code is when interacting with low-level C APIs like Core Foundation or Core Graphics.
What happens if string in is null?
When assigning the null to the string variable, the reference variable does not refer to any memory location in a heap. The null string means no string at all. It does not have a length because it’s not a string at all.
Is nil null in C?
Nil is used to represent a null pointer to an Objective-C class. NULL is used to represent a null pointer to anything else. Nil is the literal null value for Objective-C classes, corresponding to the type Class.
Is null the same as nil?
NULL and nil are equal to each other, but nil is an object value while NULL is a generic pointer value ((void*)0, to be specific). [NSNull null] is an object that’s meant to stand in for nil in situations where nil isn’t allowed. For example, you can’t have a nil value in an NSArray.
Is nil the same as null Ruby?
Well, “nil” is the traditional name for the reified concept of “nothing” in Lisp and Smalltalk†. The word “null” is used as an adjective meaning “empty”, as in “the null list,” which is nil. Meanwhile, “null” is traditionally a pointer value in C that signifies the pointer doesn’t point to anything valid.
Is empty string same as null?
The Java programming language distinguishes between null and empty strings. An empty string is a string instance of zero length, whereas a null string has no value at all. An empty string is represented as “” . It is a character sequence of zero characters.
How do you test if a string is empty in C?
To check if a given string is empty or not, we can use the strlen() function in C. The strlen() function takes the string as an argument and returns the total number of characters in a given string, so if that function returns 0 then the given string is empty else it is not empty.
Is nil same as null in Swift?
NULL has no equivalent in Swift. nil is also called nil in Swift.
What is the difference between NSString and string?
NSString is the abstract base class for a cluster of classes representing strings. Its interface does not include any methods to change the string contents after initialization. NSMutableString is the abstract base class for a cluster of classes representing strings whose contents can be changed.
Is it possible to use null in C/C++?
I am not by any stretch of the imagination a Obj-C or Cocoa expert, in C/C++ you can use something like: And, unless you explicitly, set it to NULL or changed what it was pointing to, you can be certain, that it is, in fact, Not Null or Null (what-ever you were looking for…)
How can I tell if a string is empty in Objective C?
But to my surprise this didn’t work – because my string was (null) rather than “empty” or nil, which in Objective C are not the same thing. Instead we can test for the length of this string, and if it returns zero, then we’re sure it’s empty: if ( [myString length] == 0) { // definitely empty! } // definitely empty!
Is it possible to test if a string is empty?
But to my surprise this didn’t work – because my string was (null) rather than “empty” or nil, which in Objective C are not the same thing. Instead we can test for the length of this string, and if it returns zero, then we’re sure it’s empty:
How to implement objectforkey in NSArray with nsnull?
The NSNull singleton can be used to build “interleaved” arrays like obj0, obj1, obj2, NSNull, obj3, NSNull., nil. NSArray does not implement objectForKey. Your code will crash at runtime (if clientDataArray has been allocated and initialized) You can access array elements by index ( objectAtIndex: ).