What is the difference between NSString* mystring and NSString *mystring

I've come across several examples which declares classes in the header differently like

NSStrin开发者_如何学编程g* mystring;

or

NSString *mystring;

What's the difference?

Those are three totally distinct lexical elements and the amount of whitespace in-between them is totally irrelevant. These are all equivalent in terms of what the compiler generates:

NSString*x;
NSString *x;
NSString* x;
NSString * x;
NSString                 *                 x;
NSString /* comment here */ * /* and another */ x;

I prefer the NSString *x variation since the pointer specifier belongs to the variable, not the type. By that, I mean that both of these:

int *x, y;
int* x, y;

create an integer pointer called x and an integer called y, not two integer pointers.

There is no difference. It's a matter of style.

In Objective-C, you can pretty much think of the star as part of the 'type' of the variable.

However, the compiler interprets the star as "treat this variable as a pointer to the declared type" (in this case NSString). Where it gets interesting is defining multiple variables at once:

NSString *myString, *yourString;

You must use the star on each variable.

Is preference, and is useful if you declare multiple variables in the same line, viz

NSString* mystring1, mystring2;  // Misleading, mystring2 is not a *

NSString *mystring1, mystring2;  // Is more clear 

no difference, just coding style preference.

Nothing, it isn't even important to have space between them. You can even write NSString*mystring.

There is no differences in reality.

None whatsoever - it's a personal preference as to whether you think...

1. Here comes a variable that's of type NSString pointer (NSString* mystring)

   or

2. Here comes a variable of type NSString that's a pointer (NSString *mystring)

...is more legible. That said, as long as you're consistent it isn't something you should loose sleep over.

In C (and Objective-C, as a superset of C), placement of the * is merely a matter of style.

I'd recommend checking out the relevant section from Google's style guide.

There's no difference. It's a matter of preference and style.

Advantage of the first approach:

When coding to protocols, there's no issue with some variables having a star and some not. Example:

NSString*        _myString
id<SomeProtocol> _collaborator

versus (more confusing):

NString          *_myString
id<SomeProtocol> _collaborator

Drawback to this approach: (as pointed out)

//Only the first is a pointer. 
NSString* _myString, _anotherString 

Modern OO languages (like Java) tend to discourage multiple variables on one line: http://java.sun.com/docs/codeconv/html/CodeConventions.doc5.html#2991