Placement of the asterisk in Objective-C

Question

There is no difference, however you should be aware that only the first "token" (so to speak) defines the type name, and the * is not part of the type name. That is to say:

NSString *aString, bString;

Creates one pointer-to-NSString, and one NSString. To get both to be pointers, do either:

NSString *aString, *bString;

or:

NSString *aString;
NSString *bString;

1.  NSString *string;
2.  NSString * string;
3.  (NSString *) string;
4.  NSString* string;

1, 2 and 4 are exactly identical. It's all style. Pick whatever you want, or mix it up.

Choice #3 has another meaning also, it's used in casting. For example:

t = (NSString *)string ;

will cast string to an NSString pointer.

But choice #3 is the syntax you'd probably use in a .h file or in the function definition in a .m file. Inside an actual function, in code which is "run" it has a different meaning.

There is no difference — it's a matter of style. They all declare a variable called string that's a pointer to an NSString. The parentheses are necessary in some contexts (particularly method declarations) in order to clarify that it's a type declaration.

1.  NSString *string;
2.  NSString * string;
3.  (NSString *) string;
4.  NSString* string;

1,2 and 4 are equivalent. The C language (and the Objective-C superset of C) specify a syntax that is insensitive to white space. So you can freely add spaces where you choose as a matter of style. All relevant syntax is delimited by non-whitespace characters (e.g. {, }, ;, etc.) [1].

3 is either a type cast (telling the C compiler to use the NSString* type regardless of the declared type of string. In Objective-C, type casting of object instances is rarely necessary. You can use the id type for variables that can reference instances of any object type.

In method declarations, syntax 3 (sometimes without the ending semicolon) is used to declare the type of method parameters. An Objective-C method may look like this:

- (void)myMethodThatTakesAString:(NSString*)string;

In this declaration, the type of the argument named string is type NSString* (the leading - indicates an instance method as oppose to a class method). A method declaration with more than one parameter might look like this:

- (void)myMethodTakingAString:(NSString*)string andAnInteger:(NSInteger)intParam;

[1] This is compared to languages like Python which use whitespace as a block delimeter.

it doesn't matter where you put your asterisk, all statements create pointers of type NSString.

when using multiple variable names in one line you have to write the asterisk for each variable though.

NSString * nsstring, * nsstring2;

There is no difference, where the * is placed in a pointer declaration is irrelevant.

No difference, whitespace placement is irrelevant.