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Xiao Ling
Xiao Ling

Posted on • Originally published at dynamsoft.com

Integrating Dynamsoft's C++ Barcode SDK v10 into Go Module with a C Wrapper

#go #cpp #cgo

Starting with version 10, the Dynamsoft Barcode Reader SDK has been entirely rewritten in C++, providing exclusively C++ APIs. This marks a significant departure from version 9.x, which offered both C and C++ APIs, rendering our Go module designed for version 9.x incompatible with version 10. The incompatibility arises because cgo does not directly support calling C++ APIs. In this article, we will demonstrate how to create a C wrapper to call the C++ API of Dynamsoft Barcode Reader SDK v10. Subsequently, we'll only need to update the import "C" statement to link the C wrapper library, avoiding any modifications to the existing Go wrapper code.

Prerequisites

Step 1: Getting Started with the C++ Barcode SDK

The Dynamsoft Barcode Reader v10.x includes a set of C++ libraries (for Windows x86/x64 and Linux x64), header files, and templates. After coping these components into the lib folder, the directory structure should look like this:

|- goBarcodeQrSDK
    |- lib
        |- windows
            |- DBR-PresetTemplates.json
            |- DynamicImagex64.dll
            |- DynamicPdfCorex64.dll
            |- DynamicPdfx64.dll
            |- DynamsoftBarcodeReaderx64.dll
            |- DynamsoftBarcodeReaderx64.lib
            |- DynamsoftCaptureVisionRouterx64.dll
            |- DynamsoftCaptureVisionRouterx64.lib
            |- DynamsoftCorex64.dll
            |- DynamsoftCorex64.lib
            |- DynamsoftImageProcessingx64.dll
            |- DynamsoftImageProcessingx64.lib
            |- DynamsoftLicensex64.dll
            |- DynamsoftLicensex64.lib
            |- DynamsoftUtilityx64.dll
            |- DynamsoftUtilityx64.lib
            |- vcomp140.dll
        |- linux 
            |- DBR-PresetTemplates.json
            |- libbridge.so
            |- libDynamicImage.so
            |- libDynamicPdf.so
            |- libDynamicPdfCore.so
            |- libDynamsoftBarcodeReader.so
            |- libDynamsoftCaptureVisionRouter.so
            |- libDynamsoftCore.so
            |- libDynamsoftImageProcessing.so
            |- libDynamsoftLicense.so
            |- libDynamsoftUtility.so
        |- DynamsoftBarcodeReader.h
        |- DynamsoftCaptureVisionRouter.h
        |- DynamsoftCodeParser.h
        |- DynamsoftCore.h
        |- DynamsoftDocumentNormalizer.h
        |- DynamsoftImageProcessing.h
        |- DynamsoftLabelRecognizer.h
        |- DynamsoftLicense.h
        |- DynamsoftUtility.h
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Step 2: Creating a C Wrapper with CMake

CMake C wrapper for C++

We will develop a C wrapper to bridge the C++ API of the Dynamsoft Barcode Reader SDK v10. This wrapper will be constructed using CMake. The structure of the CMakeLists.txt file is as follows:

cmake_minimum_required(VERSION 3.0.0)

project(bridge VERSION 0.1.0)

if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
    set(TARGET_LIB_DIR "${PROJECT_SOURCE_DIR}/../linux/")
elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
    set(TARGET_LIB_DIR "${PROJECT_SOURCE_DIR}/../windows/")
endif()

link_directories(${TARGET_LIB_DIR})
INCLUDE_DIRECTORIES("${CMAKE_CURRENT_BINARY_DIR}" "${PROJECT_SOURCE_DIR}/../")
add_library(bridge SHARED bridge.cpp)

if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
    target_link_libraries (${PROJECT_NAME} "DynamsoftLicense" "DynamsoftBarcodeReader" "DynamsoftCaptureVisionRouter" "DynamsoftCore")
elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
    if(CMAKE_CL_64)
        target_link_libraries (${PROJECT_NAME} "DynamsoftLicensex64" "DynamsoftBarcodeReaderx64" "DynamsoftCaptureVisionRouterx64" "DynamsoftCorex64")
    endif()
endif()

# Copy the built library to the target directory
add_custom_command(TARGET bridge POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy
    "$<TARGET_FILE:bridge>"
    "${TARGET_LIB_DIR}")
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In bridge.h, we declare C functions for cgo to invoke, and these are implemented in bridge.cpp. As we compile the C wrapper into a shared library, we utilize the add_custom_command in CMake to automate copying the compiled library into the desired directory.

Reflecting on the C API provided by Dynamsoft Barcode Reader v9.x, we will declare similar C functions in bridge.h:

#ifndef C_BRIDGING_H
#define C_BRIDGING_H

#if defined(_WIN32) || defined(_WIN64)
#define C_API __declspec(dllexport)
#else
#define C_API __attribute__((visibility("default")))
#endif

typedef struct
{
    int x1;
    int y1;
    int x2;
    int y2;
    int x3;
    int y3;
    int x4;
    int y4;

} LocalizationResult;

typedef struct
{
    char *barcodeFormatString;
    char *barcodeText;
    LocalizationResult *localizationResult;
    char reserved[44];
} TextResult;

typedef struct
{
    int resultsCount;
    TextResult *results;
} TextResultArray;

typedef enum ConflictMode
{
    CM_IGNORE = 1,
    CM_OVERWRITE = 2

} ConflictMode;

typedef struct
{
    void *cvr;
    void *result;
} BarcodeReader;

#ifdef __cplusplus
extern "C"
{
#endif
    // Create dbr9.x-like API for dbr10.x
    C_API int DBR_InitLicense(const char *pLicense, char errorMsgBuffer[], const int errorMsgBufferLen);
    C_API int DBR_DecodeFile(void *barcodeReader, const char *pFileName, const char *pTemplateName);
    C_API void *DBR_CreateInstance();
    C_API void DBR_DestroyInstance(void *barcodeReader);
    C_API const char *DBR_GetVersion();
    C_API int DBR_GetAllTextResults(void *barcodeReader, TextResultArray **pResults);
    C_API void DBR_FreeTextResults(TextResultArray **pResults);
    C_API int DBR_InitRuntimeSettingsWithString(void *barcodeReader, const char *content, const ConflictMode conflictMode, char errorMsgBuffer[], const int errorMsgBufferLen);
    C_API int DBR_InitRuntimeSettingsWithFile(void *barcodeReader, const char *pFilePath, const ConflictMode conflictMode, char errorMsgBuffer[], const int errorMsgBufferLen);

    // The interop functions for Go
    C_API TextResult *getTextResultPointer(TextResultArray *resultArray, int offset);
    C_API LocalizationResult *getLocalizationPointer(TextResult *result);
    C_API const char *getText(TextResult *result);
    C_API const char *getFormatString(TextResult *result);
#ifdef __cplusplus
}
#endif

#endif
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To ensure these C functions are properly exported on both Windows and Linux, we employ __declspec(dllexport) and __attribute__((visibility("default"))), respectively for Windows and Linux.

At the start of bridge.cpp, we include necessary C++ headers and declare the use of relevant namespaces:

#include <iostream>
#include <string>
#include <cstring>
#include "bridge.h"
#include "DynamsoftCaptureVisionRouter.h"

using namespace std;
using namespace dynamsoft::license;
using namespace dynamsoft::cvr;
using namespace dynamsoft::dbr;
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Following this setup, we proceed to implement the declared C functions.

  • DBR_InitLicense: In v10.x, the license is initialized by calling CLicenseManager::InitLicense. This initialization is not only used for the barcode reader but also for other products like the Dynamsoft Label Recognizer and Dynamsoft Document Normalizer.

    C_API int DBR_InitLicense(const char *pLicense, char errorMsgBuffer[], const int errorMsgBufferLen)
{
    int ret = CLicenseManager::InitLicense(pLicense, errorMsgBuffer, 512);
    if (ret != 0)
    {
        cout << "Error: " << errorMsgBuffer << endl;
    }
    return ret;
}

  • DBR_CreateInstance: This function creates an instance of BarcodeReader, which includes pointers to the CCaptureVisionRouter class and CCapturedResult class. Since classes are not supported in C, we use void * to represent these pointers and cast them to the actual class pointers when necessary.

    C_API void *DBR_CreateInstance()
{
    BarcodeReader *barcodeReader = new BarcodeReader;
    CCaptureVisionRouter *cvr = new CCaptureVisionRouter;
    barcodeReader->cvr = cvr;
    barcodeReader->result = NULL;
    return (void *)barcodeReader;
}

  • DBR_DestroyInstance: Releases the memory allocated for the BarcodeReader instance.

    C_API void DBR_DestroyInstance(void *barcodeReader)
{
    if (barcodeReader != NULL)
    {
        BarcodeReader *reader = (BarcodeReader *)barcodeReader;
        if (reader->cvr != NULL)
        {
            delete (CCaptureVisionRouter *)reader->cvr;
            reader->cvr = NULL;
        }

        if (reader->result != NULL)
        {
            ((CCapturedResult *)reader->result)->Release();
            reader->result = NULL;
        }

        delete reader;
        barcodeReader = NULL;
    }
}

  • DBR_DecodeFile: Decode barcodes from an image file. The results are stored in BarcodeReader->result. In v10.x, the barcode decoding function has been replaced by CCaptureVisionRouter::Capture. Depending on your template configuration, the results could vary, including data types such as text, barcode, or quadrilateral.

    C_API int DBR_DecodeFile(void *barcodeReader, const char *pFileName, const char *pTemplateName)
{
    BarcodeReader *reader = (BarcodeReader *)barcodeReader;
    if (!reader || !reader->cvr)
        return -1;

    CCapturedResult *result = ((CCaptureVisionRouter *)reader->cvr)->Capture(pFileName);
    int errorCode = result->GetErrorCode();
    if (result->GetErrorCode() != 0)
    {
        cout << "Error: " << result->GetErrorCode() << "," << result->GetErrorString() << endl;
    }

    reader->result = result;

    return errorCode;
}

  • DBR_GetVersion: Retrieves the version number of the Dynamsoft Barcode Reader SDK.

    C_API const char *DBR_GetVersion()
{
    return CBarcodeReaderModule::GetVersion();
}

  • DBR_GetAllTextResults: Extracts barcode text, format, and coordinates from the results. The CapturedResultItemType::CRIT_BARCODE enum is used to filter for the barcode data type.

    C_API int DBR_GetAllTextResults(void *barcodeReader, TextResultArray **pResults)
{
    BarcodeReader *reader = (BarcodeReader *)barcodeReader;
    if (!reader || !reader->cvr || !reader->result)
        return -1;

    CCapturedResult *result = (CCapturedResult *)reader->result;

    int capturedResultItemCount = result->GetItemsCount();
    if (capturedResultItemCount == 0)
        return -1;

    TextResultArray *textResults = (TextResultArray *)calloc(1, sizeof(TextResultArray));
    textResults->resultsCount = capturedResultItemCount;
    textResults->results = (TextResult *)calloc(capturedResultItemCount, sizeof(TextResult));
    *pResults = textResults;

    for (int j = 0; j < capturedResultItemCount; j++)
    {
        const CCapturedResultItem *capturedResultItem = result->GetItem(j);
        CapturedResultItemType type = capturedResultItem->GetType();
        if (type == CapturedResultItemType::CRIT_BARCODE)
        {
            const CBarcodeResultItem *barcodeResultItem = dynamic_cast<const CBarcodeResultItem *>(capturedResultItem);
            char *barcodeFormatString = (char *)barcodeResultItem->GetFormatString();
            char *barcodeText = (char *)barcodeResultItem->GetText();
            textResults->results[j].barcodeFormatString = (char *)malloc(strlen(barcodeFormatString) + 1);
            strcpy(textResults->results[j].barcodeFormatString, barcodeFormatString);
            textResults->results[j].barcodeText = (char *)malloc(strlen(barcodeText) + 1);
            strcpy(textResults->results[j].barcodeText, barcodeText);

            CPoint *points = barcodeResultItem->GetLocation().points;
            textResults->results[j].localizationResult = (LocalizationResult *)malloc(sizeof(LocalizationResult));
            textResults->results[j].localizationResult->x1 = points[0][0];
            textResults->results[j].localizationResult->y1 = points[0][1];
            textResults->results[j].localizationResult->x2 = points[1][0];
            textResults->results[j].localizationResult->y2 = points[1][1];
            textResults->results[j].localizationResult->x3 = points[2][0];
            textResults->results[j].localizationResult->y3 = points[2][1];
            textResults->results[j].localizationResult->x4 = points[3][0];
            textResults->results[j].localizationResult->y4 = points[3][1];
        }
    }

    result->Release();
    reader->result = NULL;

    return 0;
}

  • DBR_FreeTextResults: Releases the memory allocated for the TextResultArray.

    C_API void DBR_FreeTextResults(TextResultArray **pResults)
{
    if (pResults)
    {
        if (*pResults)
        {
            if ((*pResults)->results)
            {
                for (int i = 0; i < (*pResults)->resultsCount; i++)
                {
                    if ((*pResults)->results[i].barcodeFormatString)
                    {
                        free((*pResults)->results[i].barcodeFormatString);
                    }
                    if ((*pResults)->results[i].barcodeText)
                    {
                        free((*pResults)->results[i].barcodeText);
                    }

                    if ((*pResults)->results[i].localizationResult)
                    {
                        free((*pResults)->results[i].localizationResult);
                    }
                }
                free((*pResults)->results);
            }
        }
    }
}

  • DBR_InitRuntimeSettingsWithString: Initializes runtime settings with a JSON string.

    C_API int DBR_InitRuntimeSettingsWithString(void *barcodeReader, const char *content, const ConflictMode conflictMode, char errorMsgBuffer[], const int errorMsgBufferLen)
{
    BarcodeReader *reader = (BarcodeReader *)barcodeReader;
    if (!reader || !reader->cvr)
        return -1;

    int ret = ((CCaptureVisionRouter *)reader->cvr)->InitSettings(content, errorMsgBuffer, errorMsgBufferLen);

    if (ret != 0)
    {
        cout << "Error: " << errorMsgBuffer << endl;
    }

    return ret;
}

    The template parameters and structure have been changed in v10.x. Below is a simple example:

    {
  "CaptureVisionTemplates": [
    {
      "Name": "cv0",
      "ImageROIProcessingNameArray": [
        "roi-read-barcodes"
      ],
      "Timeout": 10000
    }
  ],
  "TargetROIDefOptions": [
    {
      "Name": "roi-read-barcodes",
      "TaskSettingNameArray": [
        "task-read-barcodes"
      ]
    }
  ],
  "BarcodeReaderTaskSettingOptions": [
    {
      "Name": "task-read-barcodes",
      "ExpectedBarcodesCount": 0,
      "BarcodeFormatIds": [ "BF_DATAMATRIX" ]
    }
  ]
}

    Note: The DBR-PresetTemplates.json file, along with the shared libraries, will be loaded by default. If you invoke the DBR_InitRuntimeSettingsWithString function, the settings specified in the JSON string will overwrite the default settings.

After completing the bridge.cpp implementation, we can compile the C wrapper into shared libraries for Windows and Linux using the commands provided below:

  • Windows:

    mkdir build
cd build
cmake -DCMAKE_GENERATOR_PLATFORM=x64 ..
cmake --build . --config Release

  • Linux:

    mkdir build
cd build
cmake ..
cmake --build . --config Release

Step 3: Integrating the C Wrapper into the Existing Go Module

To incorporate the C wrapper into our Go module, we'll need to adjust the reader.go file to link against the C wrapper's shared library. This involves the following modifications:

import (
    /*
       #cgo CXXFLAGS: -std=c++11
       #cgo CFLAGS: -I${SRCDIR}/lib -I${SRCDIR}/lib/bridge
       #cgo linux LDFLAGS: -L${SRCDIR}/lib/linux -lbridge  -Wl,-rpath=\$$ORIGIN
       #cgo windows LDFLAGS: -L${SRCDIR}/lib/windows -lbridge
       #include <stdlib.h>
       #include "bridge.h"
    */
    "C"
)
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Additionally, it's necessary to update the test code with a new template string and your personal license key within the goBarcodeQrSDK_test.go file:

var jsonString = `{
    "CaptureVisionTemplates": [
      {
        "Name": "cv0",
        "ImageROIProcessingNameArray": [
          "roi-read-barcodes"
        ],
        "Timeout": 10000
      }
    ],
    "TargetROIDefOptions": [
      {
        "Name": "roi-read-barcodes",
        "TaskSettingNameArray": [
          "task-read-barcodes"
        ]
      }
    ],
    "BarcodeReaderTaskSettingOptions": [
      {
        "Name": "task-read-barcodes",
        "ExpectedBarcodesCount": 0,
        "BarcodeFormatIds": [ "BF_DEFAULT" ]
      }
    ]
  }`

ret, _ := InitLicense("LICENSE-KEY")
ret, _ := obj.SetParameters(jsonString)
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Finally, we can compile and execute the Go module as follows:

  • Windows:

    run_windows_test.ps1

  • Linux:

    ./run_linux_test.sh

Source Code

https://github.com/yushulx/goBarcodeQrSDK/tree/dbr10

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