using CFSTR() & UTF8String in objective C

Question

When converting NSString to constants, I usually use

[@"..." UTF8String];

I was just looking over apple docs on address book programming and i see they use the macro

CFSTR("...");

Out of curiousity, I'm just wondering is there any different between the two?

Jonathan Grynspan · Accepted Answer · 2012-07-11 03:02:15Z

5

CFSTR("...") is essentially the Core Foundation equivalent of @"...". In fact, you can do the following:

const char *utf8dots = [(NSString *)CFSTR("...") UTF8String];

And you'll get the same result as you would with your first line of code.

In theory, CFSTR() creates a constant CFString, while @"" creates a constant NSString. In practice, the two types are interchangeable.

Does that help?

answered Jul 11, 2012 at 3:02

Jonathan Grynspan

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2 Comments

Just a coder Over a year ago

so basically, there is no practical difference in the value returned by CFSTR("foo") and the value returned by [@"foo" UTFTString] ?

Jonathan Grynspan Over a year ago

No, re-read. There's no practical difference between CFSTR("foo") and @"foo". -UTF8String can be sent to either and returns a third type of string, a C string encoded as UTF-8. That string isn't an object, it's a bare C pointer.

Catfish_Man · Accepted Answer · 2012-07-11 03:00:44Z

3

Those create completely different sorts of things. One gets you a CFStringRef, which is an object (well, a CFType, but that's compatible with objects). The other gets you a char*, which is just an array of chars, and not an object at all. You could, for example, do this:

[(NSString *)CFSTR("foo") UTF8String];

and that would be totally valid.

answered Jul 11, 2012 at 3:00

Catfish_Man

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2 Comments

Just a coder Over a year ago

so basically, there is no practical difference in the value returned by CFSTR("foo") and the value returned by [@"foo" UTFTString] ?

Catfish_Man Over a year ago

That's the opposite of what I said. There's no practical difference between CFSTR("foo") and @"foo". There's a HUGE difference between either of those, and the return value of -UTF8String

borrrden · Accepted Answer · 2012-07-11 02:57:36Z

1

The former doesn't actually create anything, it simply returns an internal const char pointer of an NSString (run-time function). The latter will create a compile-time constant CFStringRef value. It cannot be used with variables because those variables will not be available at compile time.

EDIT I realize that last sentence is a bit vague. You can use the result of CFSTR as a variable, but you cannot pass a variable as an argument.

edited Jul 11, 2012 at 2:57

answered Jul 11, 2012 at 2:47

borrrden

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2 Comments

Rob Napier Over a year ago

What do you mean by "it cannot be used with variables" here?

borrrden Over a year ago

If you try to insert a variable instead of a literal string you will get an error.

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