- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    
    self.title=@"GTMBase64";
    
    [self initBase64];
}
- (void)initBase64
{
    NSData *data = [@"HelloWorld" dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES];
    //编码
    NSString* encoded = [[NSString alloc] initWithData:[GTMBase64 encodeData:data] encoding:NSUTF8StringEncoding];
    NSLog(@"encoded:%@", encoded);
    //解码
    NSString* decoded = [[NSString alloc] initWithData:[GTMBase64 decodeString:encoded] encoding:NSUTF8StringEncoding];
    NSLog(@"decoded:%@", decoded);
}

2015-10-13 11:09:26.324 GTMBase64Demo[2940:97657] encoded:SGVsbG9Xb3JsZA==
2015-10-13 11:09:26.324 GTMBase64Demo[2940:97657] decoded:HelloWorld