How to convert an NSString to hex values

Question

I'd like to convert a regular NSString into an NSString with the (what I assume are) ASCII hex values and back.

I need to produce the same output that the Java methods below do, but I can't seem to find a way to do it in Objective-C. I've found some examples in C and C++ but I've had a hard time working them into my code.

Here are the Java methods I'm trying to reproduce:

/** * Encodes the given string by using the hexadecimal representation of its UTF-8 bytes. * * @param s The string to encode. * @return The encoded string. */ public static String utf8HexEncode(String s) {     if (s == null) {         return null;     }     byte[] utf8;     try {         utf8 = s.getBytes(ENCODING_UTF8);     } catch (UnsupportedEncodingException x) {         throw new RuntimeException(x);     }     return String.valueOf(Hex.encodeHex(utf8)); }  /** * Decodes the given string by using the hexadecimal representation of its UTF-8 bytes. * * @param s The string to decode. * @return The decoded string. * @throws Exception If an error occurs. */ public static String utf8HexDecode(String s) throws Exception { if (s == null) {     return null; }     return new String(Hex.decodeHex(s.toCharArray()), ENCODING_UTF8); }  

Update: Thanks to drawnonward's answer here's the method I wrote to create the hex NSStrings. It gives me an "Initialization discards qualifiers from pointer target type" warning on the char declaration line, but it works.

- (NSString *)stringToHex:(NSString *)string {     char *utf8 = [string UTF8String];     NSMutableString *hex = [NSMutableString string];     while ( *utf8 ) [hex appendFormat:@"%02X" , *utf8++ & 0x00FF];      return [NSString stringWithFormat:@"%@", hex]; } 

Haven't had time to write the decoding method yet. When I do, I'll edit this to post it for anyone else interested.

Update2: So the method I posted above actually doesn't output what I'm looking for. Instead of outputting hex values in 0-f format, it was instead outputting all numbers. I finally got back to working on this problem and was able to write a category for NSString that exactly duplicates the Java methods I posted. Here it is:

// //  NSString+hex.h //  Created by Ben Baron on 10/20/10. //  @interface NSString (hex)       + (NSString *) stringFromHex:(NSString *)str;     + (NSString *) stringToHex:(NSString *)str;  @end  // //  NSString+hex.m //  Created by Ben Baron on 10/20/10. //  #import "NSString+hex.h"  @implementation NSString (hex)  + (NSString *) stringFromHex:(NSString *)str  {        NSMutableData *stringData = [[[NSMutableData alloc] init] autorelease];     unsigned char whole_byte;     char byte_chars[3] = {'\0','\0','\0'};     int i;     for (i=0; i < [str length] / 2; i++) {         byte_chars[0] = [str characterAtIndex:i*2];         byte_chars[1] = [str characterAtIndex:i*2+1];         whole_byte = strtol(byte_chars, NULL, 16);         [stringData appendBytes:&whole_byte length:1];      }      return [[[NSString alloc] initWithData:stringData encoding:NSASCIIStringEncoding] autorelease]; }  + (NSString *) stringToHex:(NSString *)str {        NSUInteger len = [str length];     unichar *chars = malloc(len * sizeof(unichar));     [str getCharacters:chars];      NSMutableString *hexString = [[NSMutableString alloc] init];      for(NSUInteger i = 0; i < len; i++ )     {         [hexString appendString:[NSString stringWithFormat:@"%x", chars[i]]];     }     free(chars);      return [hexString autorelease]; }  @end 

Answer 1

The perfect and short way to convert nsstring to hexadecimal values

NSMutableString *tempHex=[[NSMutableString alloc] init];  [tempHex appendString:@"0xD2D2D2"];  unsigned colorInt = 0;  [[NSScanner scannerWithString:tempHex] scanHexInt:&colorInt];  lblAttString.backgroundColor=UIColorFromRGB(colorInt); 

The macro used for this code is----

#define UIColorFromRGB(rgbValue)  [UIColor \colorWithRed:((float)((rgbValue & 0xFF0000) >> 16))/255.0 \ green:((float)((rgbValue & 0xFF00) >> 8))/255.0 \ blue:((float)(rgbValue & 0xFF))/255.0 alpha:1.0] 

Answer 2

For these lines of Java

utf8 = s.getBytes(ENCODING_UTF8); new String(decodedHexString, ENCODING_UTF8); 

Objective-C equivalents would be

utf8 = [s UTF8String]; [NSString initWithUTF8String:decodedHexString]; 

To make an NSString with the hexadecimal representation of a character string:

NSMutableString *hex = [NSMutableString string]; while ( *utf8 ) [hex appendFormat:@"%02X" , *utf8++ & 0x00FF]; 

You will have to make your own decodeHex function. Just pull two characters out of the string and, if they are valid, add a byte to the result.