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User Guide - C


  • Windows
    • Windows 7, 8, 10, 2003, 2008, 2008 R2, 2012.
    • Visual Studio 2008 or above
  • Linux
    • Linux x64: Ubuntu 14.04.4+ LTS, Debian 8+, etc
    • GCC 4.2+


If you don’t have SDK yet, please go to Dynamsoft website to get it. Once the folder is decompressed, the root directory of the DLR installation package is DynamsoftLabelRecognizer, which we will refer to as [INSTALLATION FOLDER] throughout this guide.

Build Your First Application

Let’s start by creating a console application which demonstrates how to use the minimum code to recognize text from an image file.

You can download the complete source code referenced in this guide from here.

Create A New Project

For Windows

  1. Open Visual Studio. Go to File > New > Project, select Empty App and enter DLRCSample in the name text box.

  2. Add a new source file named DLRCSample.c into the project.

For Linux

  1. Create a new source file named DLRCSample.c and place it into the folder [INSTALLATION FOLDER]\Samples\DLRCSample.

  2. Create a file named Makefile and put it in the same directory as the file DLRCSample.c. The content of Makefile is as follows:

     LDFLAGS=-L $(DLRLIB_PATH) -Wl,-rpath=$(DLRLIB_PATH) -Wl,-rpath=./
     # build rule for target.
     $(TARGET): $(OBJECT)
         $(CC) -o $(TARGET) $(OBJECT) $(DLRLIB) $(LDFLAGS)
     # target to build an object file
     $(OBJECT): $(SOURCE)
         $(CC) $(CCFLAGS) $(SOURCE)
     # the clean target
     .PHONY : clean
         rm -f $(OBJECT) $(TARGET)

    Note: The DLRLIB_PATH variable should be set to the correct directory where the DLR library files are located. The files and character models directory can be found in [INSTALLATION FOLDER]/Lib/Linux.

Include the Label Recognizer Library

  1. Add headers and libs in DLRCSample.c.

     #include <stdio.h>
     #include "<relative path>/Include/DynamsoftLabelRecognizer.h"
     // The following code only applies to Windows.
     #if defined(_WIN64) || defined(_WIN32)
         #ifdef _WIN64
             #pragma comment(lib, "<relative path>/Lib/Windows/x64/DynamsoftLabelRecognizerx64.lib")
             #pragma comment(lib, "<relative path>/Lib/Windows/x86/DynamsoftLabelRecognizerx86.lib")

    Please replace <relative path> in the above code with the relative path to the DLRCSample.c file. The DynamsoftLabelRecognizer.h file can be found in [INSTALLATION FOLDER]/Include/ folder. The import lib files (only for Windows) can be found in [INSTALLATION FOLDER]/Lib/.

Initialize the Label Recognizer

  1. Initialize the license key

     char error[512];
     // 1.Initialize license.
     DLR_InitLicense("DLS2eyJvcmdhbml6YXRpb25JRCI6IjIwMDAwMSIsInByb2R1Y3RzIjoyfQ==", error, 512);


    • Network connection is required for the license to work.
    • “DLS2***” is a default free public trial license used in the sample.
    • If the license has expired, please request a trial license through the customer portal.
  2. Create an instance of Dynamsoft Label Recognizer

     // 2.Create an instance of Label Recognizer.
     void* dlr = DLR_CreateInstance();

Recognition Process and How to Use the Results

  1. Recognizing text in an image

     // 3.Recognize text from an image file.
     errorcode = DLR_RecognizeByFile(dlr, "../../SampleImages/dlr-sample-vin.png", "");
     if(errorcode != DM_OK)
         printf("%s\n", DLR_GetErrorString(errorcode));

    You can download the image dlr-sample-vin.png for testing. In addition, you can replace it with the full path of the image you want to recognize.

    For the error handling mechanism, the SDK returns Error Code for each function and provides a function DLR_GetErrorString to get the readable message. You should add codes for error handling based on your needs. Check out Error Code for full supported error codes.

  2. Get and output the recognition results

     DLR_ResultArray *pDLRResults = NULL;
     DLR_Result* result = NULL;
     DLR_LineResult *lineResult = NULL;
     int lCount, rCount, li, ri;
     // 4. Get all recognized results.
     DLR_GetAllResults(dlr, &pDLRResults);
     if (pDLRResults != NULL && pDLRResults->resultsCount > 0)
         rCount = pDLRResults->resultsCount;
         for (ri = 0; ri < rCount; ++ri)
             printf("Result %d:\n", ri);
             // Get result of each text area (also called label).
             result = pDLRResults->results[ri];
             lCount = result->lineResultsCount;
             for (li = 0; li < lCount; ++li)
                 // Get the result of each text line in the label.
                 lineResult = result->lineResults[li];
                 printf("Line result %d: %s\n", li, lineResult->text);
         printf("No data detected.\n");

    The recognition results of SDK are organized into a four-tier structure:

    • DLR_ResultArray corresponds to the results of an image
    • DLR_Result corresponds to the result of a TextArea (also called Label)
    • DLR_LineResult corresponds to the result of each TextLine in the Label
    • DLR_CharacterResult corresponds to the result of each Character in the TextLine

    The structure is shown in the figure below:

    DLR Result Structure

    Figure 1 – DLR Result Structure

Release Allocated Memory

  1. Release the allocated memory for the recognition results and instance

     if(pDLRResults != NULL)           

You can download the similar complete source code from Here.

Build and Run the Project

For windows

  1. Build the application through Visual Studio and copy the related DLL files and character models directory to the same folder as the EXE file. The DLL files and character models directory can be found in [INSTALLATION FOLDER]\Lib\Windows\[platforms].

    Note: Select the corresponding folder (x86 or x64) based on your project’s platform setting.

  2. Run the program DLRCSample.exe.

For Linux

  1. Open a terminal and change to the target directory where Makefile located in. Build the sample:

  2. Run the program DLRCSample.


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