If the data is not null-terminated, you should use -initWithData:encoding:

NSString* newStr = [[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding];

If the data is null-terminated, you should instead use -stringWithUTF8String: to avoid the extra \0 at the end.

NSString* newStr = [NSString stringWithUTF8String:[theData bytes]];

(Note that if the input is not properly UTF-8-encoded, you will get nil.)

Swift variant:

let newStr = String(data: data, encoding: .utf8)// note that `newStr` is a `String?`, not a `String`.

If the data is null-terminated, you could go though the safe way which is remove the that null character, or the unsafe way similar to the Objective-C version above.

// safe way, provided data is \0-terminatedlet newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)// unsafe way, provided data is \0-terminatedlet newStr2 = data.withUnsafeBytes(String.init(utf8String:))

You could call this method

+(id)stringWithUTF8String:(const char *)bytes.

I humbly submit a category to make this less annoying:

@interface NSData (EasyUTF8)// Safely decode the bytes into a UTF8 string- (NSString *)asUTF8String;@end

and

@implementation NSData (EasyUTF8)- (NSString *)asUTF8String {    return [[NSString alloc] initWithData:self encoding:NSUTF8StringEncoding];    }@end

(Note that if you're not using ARC you'll need an autorelease there.)

Now instead of the appallingly verbose:

NSData *data = ...[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

You can do:

NSData *data = ...[data asUTF8String];