How To Create a Structured Append QR Code

How To Create a Structured Append QR Code

Example, if you have a base64 string, which you want to encode with several QR-Codes linked together, follow these steps:

• Divide the base64 string into manageable sub-strings. The upper limit for a sub-string size is around 2,000 characters, but it depends on factors like scanner capabilities, available space, and print resolution. Generate a separate QR Code for each sub-string.
• Set the Structured-Append Header in each QR Code, specifying the total number of concatenated codes, the current index, and the parity byte. Calculate the parity byte over the entire string, not per individual code. The Structured-Append Header helps the scanner determine how many QR Codes need to be read and whether the data is correct.

Below is a sample C++ function for saving a QR Code with an Append Header:

ERRCODE SaveStructAppendQRCode(LPCSTR path, LPCSTR dataStr, int dataLen, int count, int index, BYTE parity)
{
  ERRCODE eCode = ErrOk;
  t_BarCode* pBarCode = NULL;   // barcode handle
  double const dpi = 300;
  RECT rect = { 0,0,255,255 };

  if (eCode == ErrOk)
    eCode = BCAlloc(&pBarCode);
  if (eCode == ErrOk)
    eCode = BCSetBCType(pBarCode, eBC_QRCode);
  if (eCode == ErrOk)
    eCode = BCSet_QR_Append(pBarCode, count, index, parity);
  if (eCode == ErrOk)
   eCode = BCSetTextA(pBarCode, dataStr, dataLen);
  if (eCode == ErrOk)
    eCode = BCCreate(pBarCode);

  if (eCode == ErrOk)
    eCode = BCSetDPI(pBarCode, dpi, dpi);
  if (eCode == ErrOk)
    eCode = BCSetIgnoreDpiFromDC(pBarCode, TRUE);
  if (eCode == ErrOk)
    eCode = BCSetSizeMode(pBarCode, e_SizeMode::eSizeMode_FitToBoundingRect);
  if (eCode == ErrOk)
    eCode = BCGetOptimalBitmapSize(pBarCode, &rect, 3, 3);

  if (eCode == ErrOk)
    eCode = BCSaveImageA(pBarCode, path, eIMBmp, rect.right, rect.bottom, dpi, dpi);
  // use BCSaveImageEx for color bitmap

  if(pBarCode)
    BCFree(pBarCode);

  return eCode;
}

Next, you create individual QR Codes with Structured Append Headers as shown below:

  ERRCODE eCode = ErrOk;
  const char* base64Str = "Your base64 string goes here...";
  int base64Len = strlen(base64Str);

  if (base64Len > 400)
  {
    BYTE parity = BCCalcStructApp_ParityA(base64Str, base64Len);

    if (eCode == ErrOk)
       eCode = SaveStructAppendQRCode("c:\\temp\\qrcode_3-1.bmp", &base64Str[0], 200, 3, 1, parity);
    if (eCode == ErrOk)
      eCode = SaveStructAppendQRCode("c:\\temp\\qrcode_3-2.bmp", &base64Str[200], 200, 3, 2, parity);
    if (eCode == ErrOk)
      eCode = SaveStructAppendQRCode("c:\\temp\\qrcode_3-3.bmp", &base64Str[400], base64Len - 400, 3, 3, parity);
  }

  if (eCode != ErrOk)
  {
    char szErr[255];
    BCGetErrorText(eCode, szErr, 255);
    printf(szErr);
  }

• Adjust the size of the barcode or the size of a matrix point using the ScaleX and ScaleY parameters in the BCGetOptimalBitmapSize(..) function.
• BCSaveImage(..) generates a monochrome BMP. For a color BMP, use BCSaveImageEx(..) or use the BitmapToFile(..) function.