How do I convert an NSString value to NSData?

Question

How do I convert an NSString value to NSData?

score 1446 · Answer 1 · edited Aug 05 '12 at 15:59

1446

NSString* str = @"teststring";
NSData* data = [str dataUsingEncoding:NSUTF8StringEncoding];

edited Aug 05 '12 at 15:59

ldiqual

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answered May 23 '09 at 11:34

flitzwald

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What are the pros and cons of using UTF-8 as opposed to something higher like UTF-16 or UTF-32? – Albert Renshaw Jan 13 '14 at 02:34
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The NSData doesn't care much about whether it is UTF-8 or UTF-16 or UTF-32. There are two problems: One, UTF-16 and UTF-32 need to have the right byte-ordering. Two, whoever converts it back to an NSString* must know the encoding, and often will assume UTF-8 encoding. Generally, UTF-8 is most likely to be handled correctly. – gnasher729 Mar 20 '14 at 17:50
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@bendytree actually no it doesn't, -dataUsingEncoding: will return an non-null-terminated string which is what stringWithUTF8String: requires, you're bounds to read memory you don't want. What converts it back is: -initWithData:encoding:. – Psycho May 05 '14 at 17:38
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@Albert Renshaw currently (no guarantee of things staying this way) `NSString` uses UTF-16 internally so there might be a slight performance gain because it does not have to do a UTF-16 <-> UTF-8 conversion. Personally, we prefer (as @gnasher729 suggests) robustness over performance and use UTF-8 everywhere. – Some Developer Oct 21 '14 at 01:32
macOS and my app are not running on big endian cpus, so I prefer utf16. – Tom Sep 16 '21 at 19:58

score 68 · Answer 2 · edited May 27 '15 at 10:22

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NSString *str = @"helowrld";
// This converts the string to an NSData object
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

you can take reference from this link

edited May 27 '15 at 10:22

Raptor

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answered Mar 10 '15 at 12:39

ALOK KUMAR

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One liner solution: `NSData *data = [@"helowrld" dataUsingEncoding:NSUTF8StringEncoding];` – Raptor May 27 '15 at 10:22

score 35 · Answer 3 · edited Oct 29 '18 at 09:35

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Do:

NSData *data = [yourString dataUsingEncoding:NSUTF8StringEncoding];

then feel free to proceed with NSJSONSerialization:JSONObjectWithData.

Correction to the answer regarding the NULL terminator

Following the comments, official documentation, and verifications, this answer was updated regarding the removal of an alleged NULL terminator:

As documented by dataUsingEncoding::

Return Value

The result of invoking dataUsingEncoding:allowLossyConversion: with NO as the second argument
As documented by getCString:maxLength:encoding: and cStringUsingEncoding::

note that the data returned by dataUsingEncoding:allowLossyConversion: is not a strict C-string since it does not have a NULL terminator

edited Oct 29 '18 at 09:35

Cœur

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answered Oct 25 '11 at 19:47

Andrew Kolesnikov

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This is WRONG! Please see my post here: http://stackoverflow.com/q/14087094/192819 – jpswain Dec 30 '12 at 00:06
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Yup. `dataUsingEncoding:` does not return null-terminated data. Only `UTF8String` and other methods that return a C string return a null-terminated string. – Peter Hosey Dec 30 '12 at 01:51
@PeterHosey do you have any source for that? I am having a hard time finding that in any docs. – shortstuffsushi Jun 18 '15 at 18:05
@shortstuffsushi: The methods that take or return a C string are expressly documented so; for example: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/index.html#//apple_ref/occ/instp/NSString/UTF8String You can verify this for other methods, such as `dataUsingEncoding:`, by inspecting the data's length and bytes. (Note that some encodings, such as UTF-16, will emit 0x00 bytes! But those aren't terminators; they're part of larger code units. And it is possible to have a U+0000, which will be encoded as such, but is not a terminator.) – Peter Hosey Aug 06 '15 at 06:25
@shortstuffsushi To wit: `const unichar buffer[1] = { 0x0000 }; NSString *string = [NSString stringWithCharacters:buffer length:1]; NSData *data = [string dataUsingEncoding:NSUTF16BigEndianStringEncoding]; NSLog(@"%lu %@", (unsigned long int)data.length, data);` – Peter Hosey Aug 06 '15 at 06:25
@shortstuffsushi And please do file bugs against the docs: https://bugreport.apple.com/ – Peter Hosey Aug 06 '15 at 06:27
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Thanks @PeterHosey, the docs you linked there *do* explicitly state the lack of NULL termination -- `(note that the data returned by dataUsingEncoding:allowLossyConversion: is not a strict C-string since it does not have a NULL terminator)`. I must have missed this earlier. I'll be sure to write up anything in the future, though. – shortstuffsushi Aug 06 '15 at 14:37
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(For anyone who's wondering: shortstuffsushi's quote is under `cStringUsingEncoding:`. I was looking under `dataUsingEncoding:`.) – Peter Hosey Aug 21 '15 at 05:03
@jpswain the author of the post didn't visit StackOverflow in the past 4 years and the score of the answer is too high for a reversal, so I've made a clear correction directly. Maybe users with 20,000+ reputation could vote to delete the answer, as what is left correct is duplicate information from other answers. – Cœur Oct 29 '18 at 09:38

score 20 · Answer 4 · answered Mar 03 '15 at 15:28

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In case of Swift Developer coming here,

to convert from NSString / String to NSData

var _nsdata = _nsstring.dataUsingEncoding(NSUTF8StringEncoding)

answered Mar 03 '15 at 15:28

Sruit A.Suk

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Shamsiddin Saidov · Answer 5 · 2017-01-08T04:36:58.067

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Objective-C:

NSString *str = @"test string";
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:str];
NSString *thatStr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

Swift:

let str = "test string"
let data = NSKeyedArchiver.archivedData(withRootObject: str)
let thatStr = NSKeyedUnarchiver.unarchiveObject(with: data) as! String

edited Jan 08 '17 at 04:36

answered Mar 26 '16 at 23:03

Shamsiddin Saidov

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Probably processor-intensive compared to the other methods, but very useful if you're accessing the file system for persistence – Stephen J Nov 28 '17 at 18:05

score 10 · Answer 6 · edited Jan 18 '13 at 13:53

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First off, you should use dataUsingEncoding: instead of going through UTF8String. You only use UTF8String when you need a C string in that encoding.

Then, for UTF-16, just pass NSUnicodeStringEncoding instead of NSUTF8StringEncoding in your dataUsingEncoding: message.

edited Jan 18 '13 at 13:53

Michael Mior

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answered Sep 13 '12 at 08:02

Jerry Thomsan

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score 7 · Answer 7 · answered Nov 01 '16 at 07:59

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For Swift 3, you will mostly be converting from String to Data.

let myString = "test"
let myData = myString.data(using: .utf8)
print(myData) // Optional(Data)

answered Nov 01 '16 at 07:59

jacks205

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score 7 · Answer 8 · answered Mar 14 '19 at 08:30

Objective-C:

NSString to NSData:

NSString* str= @"string";
NSData* data=[str dataUsingEncoding:NSUTF8StringEncoding];

NSData to NSString:

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

Swift:

String to Data:

var testString = "string"
var somedata = testString.data(using: String.Encoding.utf8)

Data to String:

var backToString = String(data: somedata!, encoding: String.Encoding.utf8) as String!

score 6 · Answer 9 · edited Nov 27 '15 at 21:02

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NSString *str = @"hello";
NSData *data = [NSData dataWithBytes:str.UTF8String length:str.length];

edited Nov 27 '15 at 21:02

Undo

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answered Nov 27 '15 at 17:46

Nex Mishra

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This answer is wrong when `str` contains code points larger than 127. This is because `str.length` gives the number of Unicode characters, not the number of bytes. For example, if `str` is `@"にほんご"`, `str.length` gives 4 while `str.UTF8String` actually contains 12 bytes. Even if you replace `str.length` by `strlen(str.UTF8String)`, it will still be wrong for the case where `str` contains the NULL character, such as `@"にほ\0んご"`. – Pang Feb 24 '16 at 06:56
A NSData object created in this way throw exeption when using with [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:&error]; – Blazej SLEBODA Feb 03 '17 at 07:21

score 5 · Answer 10 · answered Jun 29 '21 at 04:22

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Update Swift 5.x

let str = "teststring"
let data = str.data(using: .utf8)

answered Jun 29 '21 at 04:22

AnLT

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score 4 · Answer 11 · edited Nov 10 '22 at 05:57

Swift:

Swift 5.x

let myStringToConvert = "My String to Convert in Data"
let myData = myStringToConvert.data(using: .utf8)

String to Data:

var myStringToConvert = "My String to Convert in Data"
var myData = myStringToConvert.data(using: String.Encoding.utf8)

Data to String:

var backToMyString = String(data: myData!, encoding: String.Encoding.utf8) as String!

OBJECTIVE C:

NSString to NSData :

NSString* myStringToConvert= @"My String to Convert in Data";
NSData* myData=[str dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:NO];

NSData to NSString :

NSString* backToMyString = [[NSString alloc] initWithData: myData encoding:NSUTF8StringEncoding];

score 1 · Answer 12 · answered Apr 13 '18 at 21:37

1

NSString *str = @"Banana";
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:true];

answered Apr 13 '18 at 21:37

Kamani Jasmin

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score 0 · Answer 13 · answered Apr 17 '18 at 06:19

0

Objective-C

NSString *str = @"Hello World";
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:NO];

Swift

let str = "Hello World"
let data = string.data(using: String.Encoding.utf8, allowLossyConversion: false)

answered Apr 17 '18 at 06:19

Rohit Makwana

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score 0 · Answer 14 · answered Jun 29 '21 at 04:31

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In Swift there is an API which returns a non-optional

let str = "teststring"
let data = Data(str.utf8)

answered Jun 29 '21 at 04:31

vadian

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How do I convert an NSString value to NSData?

14 Answers14

Correction to the answer regarding the NULL terminator

Return Value

Linked