NSString *str = @"hogehoge";
NSMutableString *result = [NSMutableString string];
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
NSLog(@"data: %@", data); // data: <686f6765 686f6765>
const unsigned char *bytes = [data bytes];
for (int i=0; i<[data length]; i++) {
[result appendFormat:@"%X", bytes[i]];
}
NSLog(@"result: %@"