NSString to ByteArray and back

Question

I am implementing an interface, which specifies writeBytes() and readBytes() on a file. The data has to be transported as JSON.

For readBytes I do the following: 1. NSFileHandle readDataofLength - to read from a file 2. NSString initWithData: encoding: - to specify a given encoding 3. NSString getBytes:buffer 4. put each buffer[i] into a JSON array for transport : [116,101,115,116] for example "test" as UTF-8

On the other hand writeBytes should be doing about the same: 1. Parse the JSON array to a NSArray 2. NSArray getObjects:buffer - the conversion up to this point is successful 3. NSString initWithBytes:buffer length: encoding: - is not working, the return value is null 4. NSData dataUsingEncoding: 5. NSFileHandle writeData

Apparently NSString initWithBytes cannot handle buffers with content such as [116,101,115,116]. Is there any other way to convert a NSString into a ByteArray and back ?

Thanks

Answer 1

Are you using the NSUnicodeStringEncoding encoding ? If so, then you may have to prefix your bytes with a valid B.O.M (See NSString reference, section "Interpreting UTF-16-encoded data").

Have you made a test with the NSASCIIStringEncoding to check that your code works for simple case ?

Answer 2

Have you verified that the bytes within the array are a valid UTF-8 representation of a string? (http://en.wikipedia.org/wiki/UTF-8)

If not, you'll get back nil:

#import <Foundation/Foundation.h>

int
main()
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    char ary[] = { 116, 101, 115, 116, 255 };

    NSString *s = [[NSString alloc] initWithBytes: ary length: 5 encoding: NSASCIIStringEncoding];
    NSString *s2 = [[NSString alloc] initWithBytes: ary length: 5 encoding: NSUTF8StringEncoding];
    NSLog(@"s: %@, s2: %@", s, s2);

    [pool release];
}

When run, this prints:

2010-01-13 14:08:23.315 a.out[50653:903] s: testÿ, s2: (null)