URL encode/decode

//encoding
NSString *escapedUrlString = (NSString *)CFURLCreateStringByAddingPercentEscapes(
        NULL,
        (CFStringRef)plainString,
        NULL,
        (CFStringRef)@"!*'();:@&=+$,/?%#[]",
        kCFStringEncodingUTF8 );
 
//decoding
NSString *decodedUrlString = (NSString *) CFURLCreateStringByReplacingPercentEscapesUsingEncoding(
        NULL,
        (CFStringRef) escapedUrlString,
        CFSTR(""),
        kCFStringEncodingUTF8);