//NSString+URLEncoding.h  

1. #import   
2. @interface NSString (URLEncodingAdditions)  
3. - (NSString *)URLEncodedString;  
4. - (NSString *)URLDecodedString;  
5. @end</span>  

//NSString+URLEncoding.m  

1. #import "NSString+URLEncoding.h"  
2. @implementation NSString (OAURLEncodingAdditions)  
3. - (NSString *)URLEncodedString  
4. {  
5.     NSString *result = (NSString *)  
6.        CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,  
7.                                                   (CFStringRef)self,  
8.                                                   NULL,  
9.                                                   CFSTR("!*'();:@&=+$,/?%#[] "),  
10.                                                   kCFStringEncodingUTF8);  
11.     [result autorelease];  
12. return result;  
13. }  
14. - (NSString*)URLDecodedString  
15. {  
16.     NSString *result = (NSString *)  
17.        CFURLCreateStringByReplacingPercentEscapesUsingEncoding(kCFAllocatorDefault,  
18.                         (CFStringRef)self,  
19.                         CFSTR(""),  
20.                         kCFStringEncodingUTF8);  
21.     [result autorelease];  
22. return result;  
23. }  
24. @end</span>