Unfamiliar C syntax in Objective-C context

Question

I am coming to Objective-C from C# without any intermediate knowledge of C. (Yes, yes, I will need to learn C at some point and I fully intend to.) In Apple's Certificate, Key, and Trust Services Programming Guide, there is the following code:

static const UInt8 publicKeyIdentifier[] = "com.apple.sample.publickey\0";
static const UInt8 privateKeyIdentifier[] = "com.apple.sample.privatekey\0";

I have an NSString that I would like to use as an identifier here and for the life of me I can't figure out how to get that into this data structure. Searching through Google has been fruitless also. I looked at the NSString Class Reference and looked at the UTF8String and getCharacters methods but I couldn't get the product into the structure.

What's the simple, easy trick I'm missing?

Answer 1

Those are C strings: Arrays (not NSArrays, but C arrays) of characters. The last character is a NUL, with the numeric value 0.

“UInt8” is the CoreServices name for an unsigned octet, which (on Mac OS X) is the same as an unsigned char.

static means that the array is specific to this file (if it's in file scope) or persists across function calls (if it's inside a method or function body).

const means just what you'd guess: You cannot change the characters in these arrays.

\0 is a NUL, but including it explicitly in a "" literal as shown in those examples is redundant. A "" literal (without the @) is NUL-terminated anyway.

C doesn't specify an encoding. On Mac OS X, it's generally something ASCII-compatible, usually UTF-8.

To convert an NSString to a C-string, use UTF8String or cStringUsingEncoding:. To have the NSString extract the C string into a buffer, use getCString:maxLength:encoding:.