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Read and Write Bytes in a Barcode - Windows C DLL

This tutorial shows how to create a barcode by encoding raw binary data, then how to decode that data from the barcode in a Windows C DLL application using the LEADTOOLS SDK. This can be useful when using characters from extended character sets.

Overview
Summary	This tutorial covers how to encode and decode raw binary data from a barcode in a Windows C DLL Application.
Completion Time	30 minutes
Visual Studio Project	Download tutorial project (19 KB)
Platform	Windows C DLL Application
IDE	Visual Studio 2017, 2019, 2022
Development License	Download LEADTOOLS
Try it in another language	C#: .NET 6+ (Console) Swift: macOS Console C API: C DLL (Windows) Python: Python

Required Knowledge

Get familiar with the basic steps of creating a project and loading/displaying images by reviewing the Add References and Set a License and Load, Display, and Save Images tutorials, before working on the Read and Write Bytes in a Barcode - Windows C DLL tutorial.

Create the Project and Add LEADTOOLS References

Start with a copy of the project created in the Load, Display, and Save Images tutorial. If the project is not available, create it by following the steps in that tutorial.

To read and write barcodes using LEADTOOLS, add the required header and library files. Open the pre-compiled header file (either pch.h or stdafx.h, depending on the version of Visual Studio used) and add the following lines:

#include "C:\LEADTOOLS23\Include\Ltbar.h" 
 
#pragma comment (lib, "C:\\LEADTOOLS23\\Lib\\CDLL\\x64\\Ltbar_x.lib") // Barcode support

Note

For a complete list of DLLs that are required for your application, refer to Files to be Included with your Application - C API.

Set the License File

The License unlocks the features needed for the project. It must be set before any toolkit functionality is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.

There are two types of runtime licenses:

Evaluation license, obtained at the time the evaluation toolkit is downloaded. It allows the toolkit to be evaluated.
Deployment license. If a Deployment license file and developer key are needed, refer to Obtaining a License.

Note

Adding LEADTOOLS references and setting a license are covered in more detail in the Add References and Set a License tutorial.

Add the Encode and Decode Barcode Code

With the project created, the references added, the license set, and the load image code added, coding can begin.

In the Solution Explorer, double-click the resources file (.rc).

Add a new &Barcode drop down menu next to the File menu. Add two menu items in the table below to the newly-added &Barcode menu.

Menu Item Text	`Item ID`
&Encode Data	`ID_BARCODE_ENCODEDATA`
&Decode Data	`ID_BARCODE_DECODEDATA`

Navigate to the WndProc function, and under the switch (wmId) statement below the WM_COMMAND case, add two new cases below.

switch (wmId) 
{ 
case ID_BARCODE_ENCODEDATA: 
{ 
   wchar_t strUnicodeTxt[] = L"This is a Unicode string. It can be in any Unicode-supported language, which means it can include non-ASCII characters."; 
   CreateBarcode(hWnd, (BYTE*)strUnicodeTxt, sizeof strUnicodeTxt); 
} 
break; 
case ID_BARCODE_DECODEDATA: 
{ 
   BYTE* pData = NULL; 
   L_INT nDataSize = 0; 
   ReadBarcode(hWnd, &pData, &nDataSize); 
   if (pData) 
   { 
      if(IsTextUnicode(pData, nDataSize, NULL)) 
         MessageBoxW(hWnd, (wchar_t*)pData, L"Decoded Text", 0); 
      else 
         MessageBox(hWnd, TEXT("Data doesn't appear to be Unicode string"), TEXT("Barcode Tutorial"), MB_ICONERROR); 
      delete pData; // Must free it here, since it was allocated inside the ReadBarcode() function. 
   } 
} 
break; 
// Keep rest of the code as is

Add two new functions above the WndProc function named CreateBarcode and ReadBarcode.

Add the below code to the CreateBarcode function to create a new QR barcode.

void CreateBarcode(HWND hwnd, BYTE * pData, L_INT nDataLen) 
{ 
   if (LEADBmp.Flags.Allocated) 
      L_FreeBitmap(&LEADBmp); 
   L_CreateBitmap(&LEADBmp, sizeof BITMAPHANDLE, TYPE_CONV, 2000, 1600, 24, ORDER_BGR, NULL, BOTTOM_LEFT, NULL, 0); 
   L_FillBitmap(&LEADBmp, RGB(255, 255, 255)); 
 
   if (L_BarCodeInit(BARCODES_QR_WRITE) != SUCCESS) 
      return; 
 
   BARCODEDATA BarCodeData = { 0 }; 
   BARCODECOLOR BarColor = { 0 }; 
   BARCODEWRITEQR BarCodeQR = { 0 }; 
 
   BarColor.uStructSize = sizeof(BARCODECOLOR); 
   BarColor.dwColorBar = RGB(0, 0, 0); 
   BarColor.dwColorSpace = RGB(255, 255, 255); 
 
   BarCodeData.uStructSize = sizeof(BarCodeData); 
   BarCodeData.rcBarLocation.left = 50; 
   BarCodeData.rcBarLocation.top = 250; 
   BarCodeData.rcBarLocation.right = 650; 
   BarCodeData.rcBarLocation.bottom = 550; 
   BarCodeData.nUnits = BARCODE_SCANLINES_PER_PIXELS; 
   BarCodeData.ulType = BARCODE_QR_M1_DEF; // Default Model 1 QR Code size  
   BarCodeData.pszBarCodeData = (L_CHAR*)pData; 
   BarCodeData.nSizeofBarCodeData = nDataLen; 
 
   BarCodeQR.uStructSize = sizeof(BarCodeQR); 
   BarCodeQR.ulFlags = BARCODE_JUSTIFY_H_CENTER | BARCODE_JUSTIFY_V_CENTER; 
 
   //Write the barcode  
   if (SUCCESS == L_BarCodeWrite(&LEADBmp, &BarCodeData, &BarColor, BARCODE_USECOLORS, NULL, NULL, NULL, &BarCodeQR, NULL, NULL, NULL, NULL)) 
      InvalidateRect(hwnd, NULL, TRUE); 
   else 
      MessageBox(hwnd, TEXT("Could Not Write QR Barcode"), TEXT("Barcode Tutorial"), MB_ICONERROR); 
   L_BarCodeExit(); 
}

Add the below code to the ReadBarcode function to recognize and decode the created QR barcode.

void ReadBarcode(HWND hwnd, BYTE** ppData, L_INT * pDataSize) 
{ 
   *pDataSize = 0; 
   if (L_BarCodeInit(BARCODES_QR_READ) != SUCCESS) 
      return; 
   pBARCODEDATA pBarCodes = NULL; 
   BARCODECOLOR BarColor = { 0 }; 
   BarColor.uStructSize = sizeof BARCODECOLOR; 
   BarColor.dwColorBar = RGB(0, 0, 0); 
   BarColor.dwColorSpace = RGB(255, 255, 255); 
   // Search for QR barcodes in the entire bitmap 
   if (SUCCESS == L_BarCodeRead(&LEADBmp, NULL, BARCODE_QR_CODE, BARCODE_SCANLINES_PER_PIXELS, BARCODE_BLOCK_SEARCH, 0, NULL, NULL, &BarColor, &pBarCodes, sizeof BARCODEDATA)) 
   { 
      if (pBarCodes->ulType & BARCODE_QR_DEF) 
      { 
         BYTE* pData = new BYTE[pBarCodes->nSizeofBarCodeData]; 
         CopyMemory(pData, pBarCodes->pszBarCodeData, pBarCodes->nSizeofBarCodeData); 
         *ppData = pData; // IMPORTANT: must be freed by caller 
         *pDataSize = pBarCodes->nSizeofBarCodeData; 
      } 
      else 
         MessageBox(hwnd, TEXT("Barcode is not QR type"), TEXT("Barcode Tutorial"), MB_ICONERROR); 
   } 
   else 
      MessageBox(hwnd, TEXT("Could not read QR Barcode"), TEXT("Barcode Tutorial"), MB_ICONERROR); 
 
   if (pBarCodes) 
      L_BarCodeFree(&pBarCodes); 
   L_BarCodeExit(); 
}

Run the Project

Run the project by pressing F5, or by selecting Debug -> Start Debugging.

If the steps were followed correctly, the application should run. Select Barcode -> Encode Data to create an image and write on it a QR barcode containing the data. Select Barcode -> Decode Data to have the application run barcode recognition, then decode the contents of the QR code and if the data represents a Unicode string, display the text.

Barcode data decoding result message box

Wrap-up

This tutorial covered how to write and read binary data in QR barcodes using the LEADTOOLS SDK in a Windows API application. It also covered how to use the BARCODEDATA structure with the L_BarCodeRead and L_BarCodeWrite functions.