QR code reader for iPhone

Question

I want to create QR code reader based application.

Using which library, I can create my application ?

Note: I searched in google. Always I am getting

Answer 1

AVCaptureMetaDataOutput - Starting from iOS 7

Scan UPCs, QR codes, and barcodes of all varieties with AVCaptureMetaDataOutput, new to iOS 7. All you need to do is set it up as the output of an AVCaptureSession, and implement the captureOutput:didOutputMetadataObjects:fromConnection: method accordingly:

 @import AVFoundation;

 AVCaptureSession *session = [[AVCaptureSession alloc] init];
 AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
 NSError *error = nil;

 AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                error:&error];
 if (input) {
     [session addInput:input];
 } else {
     NSLog(@"Error: %@", error);
 }

 AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
 [output setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
 [output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
 [session addOutput:output];

 [session startRunning];

 #pragma mark - AVCaptureMetadataOutputObjectsDelegate

 - (void)captureOutput:(AVCaptureOutput *)captureOutput
         didOutputMetadataObjects:(NSArray *)metadataObjects
              fromConnection:(AVCaptureConnection *)connection
   {
    NSString *QRCode = nil;
     for (AVMetadataObject *metadata in metadataObjects) {
       if ([metadata.type isEqualToString:AVMetadataObjectTypeQRCode]) {
            // This will never happen; nobody has ever scanned a QR code... ever
             QRCode = [(AVMetadataMachineReadableCodeObject *)metadata stringValue];
             break;
          }
      }

     NSLog(@"QR Code: %@", QRCode);
   }

AVFoundation supports every code you've heard of (and probably a few that you haven't):

AVMetadataObjectTypeUPCECode
AVMetadataObjectTypeCode39Code
AVMetadataObjectTypeCode39Mod43Code
AVMetadataObjectTypeEAN13Code
AVMetadataObjectTypeEAN8Code
AVMetadataObjectTypeCode93Code
AVMetadataObjectTypeCode128Code
AVMetadataObjectTypePDF417Code
AVMetadataObjectTypeQRCode
AVMetadataObjectTypeAztecCode