Generating C/C++ Dynamically Linked Libraries from MATLAB Code

Dynamic Libraries Generated by MATLAB Coder

By default, when MATLAB® Coder™ generates a dynamic library (DLL):

  • The DLL is suitable for the platform that you are working on.

  • The DLL uses the release version of the C run-time library.

  • The DLL linkage conforms to the target language, by default, C. If you set the target language to C++, the linkage conforms to C++.

  • When the target language is C, the generated header files explicitly declare the exported functions to be extern "C" to simplify integration of the DLL into C++ applications.

  • When an executable that uses the DLL runs, the DLL must be on the system path so that the executable can access it.

If you generate a DLL that uses dynamically allocated variable-size data, MATLAB Coder provides exported utility functions to interact with this data in the generated code. For more information, see Utility Functions for Creating emxArray Data Structures.

Generate a C Dynamically Linked Library Using the MATLAB Coder App

This example shows how to generate a C DLL from MATLAB code using the MATLAB Coder app.

Create the Entry-Point Functions

Write two MATLAB functions, ep1 and ep2. ep1 takes one input, a single scalar. ep2 takes two inputs that are double scalars. In a local writable folder:

  1. Create a MATLAB file, ep1.m, that contains:

    function y = ep1(u) %#codegen
y = u;

  2. Create a MATLAB file, ep2.m, that contains:

    function y = ep2(u, v) %#codegen
y = u + v;

Create the Test File

In the folder that contains ep1.m and ep2.m, create a MATLAB file, ep_test.m, that calls ep1 and ep2 with example inputs.

function [y, y1] = ep_test
y = ep1(single(2));
y1 = ep2(double(3), double(4));

Open the MATLAB Coder App

On the MATLAB Toolstrip Apps tab, under Code Generation, click the MATLAB Coder app icon.

The app opens the Select Source Files page.

Specify Source Files

  1. On the Select Source Files page, type or select the name of the entry-point function ep1.

    The app creates a project with the default name ep1.prj in the current folder.

  2. To add ep2 to the list of entry-point functions, click Add Entry-Point Function. Type or select the name of the entry-point function ep2.

  3. Click Next to go to the Define Input Types step. The app analyzes the functions for coding issues and code generation readiness. If the app identifies issues, it opens the Review Code Generation Readiness page where you can review and fix issues. In this example, because the app does not detect issues, it opens the Define Input Types page.

Define Input Types

Because C uses static typing, at compile time, MATLAB Coder must determine the properties of all variables in the MATLAB files. You must specify the properties of all entry-point function inputs. From the properties of the entry-point function inputs, MATLAB Coder can infer the properties of all variables in the MATLAB files.

Specify a test file that MATLAB Coder can use to automatically define types:

  1. Enter or select the test file ep_test.m.

  2. Click Autodefine Input Types.

    The test file, eps_test.m, calls the entry-point functions ep1 and ep2 with the example input types. MATLAB Coder infers that for ep1, input u is single(1x1). For ep2, u and v are double(1x1).

  3. Click Next to go to the Check for Run-Time Issues step.

Check for Run-Time Issues

The Check for Run-Time Issues step generates a MEX file from your entry-point functions, runs the MEX function, and reports issues. This step is optional. However, it is a best practice to perform this step. You can detect and fix run-time errors that are harder to diagnose in the generated C code.

  1. To open the Check for Run-Time Issues dialog box, click the Check for Issues arrow .

    The app populates the test file field with ep_test, the test file that you used to define the input types.

  2. Click Check for Issues.

    The app generates a MEX function named ep1_mex for ep1 and ep2. It runs the test file ep_test replacing calls to ep1 and ep2 with calls to the MEX function. If the app detects issues during the MEX function generation or execution, it provides warning and error messages. Click these messages to navigate to the problematic code and fix the issue. In this example, the app does not detect issues.

  3. Click Next to go to the Generate Code step.

Generate C Code

  1. To open the Generate dialog box, click the Generate arrow .

  2. In the Generate dialog box, set Build type to Dynamic Library and Language to C. Use the default values for the other project build configuration settings.

  3. Click Generate.

    The app indicates that code generation succeeded. It displays the source MATLAB files and generated output files on the left side of the page. On the Variables tab, it displays information about the MATLAB source variables. On the Target Build Log tab, it displays the build log, including compiler warnings and errors. By default, in the code window, the app displays the C source code file, ep1.c. To view a different file, in the Source Code or Output Files pane, click the file name.

    On Microsoft® Windows® systems, MATLAB Coder generates a C dynamic library, ep1.dll, and supporting files, in the default folder, codegen\dll\ep1. It generates the minimal set of #include statements for header files required by the selected code replacement library. On Linux®, it generates a shared object (.so) file. On Mac, it generates a dynamic library (.dylib) file. The DLL linkage conforms to the target language, in this example, C. If you set the target language to C++, the linkage conforms to C++. MATLAB Coder generates a standalone C static library mcadd in the codegen\lib\mcadd folder.

  4. To view the code generation report, click View Report.

  5. Click Next to open the Finish Workflow page.

Review the Finish Workflow Page

The Finish Workflow page indicates that code generation succeeded. It provides a project summary and links to generated output.

Generate a C Dynamic Library at the Command Line

This example shows how to generate a C dynamic library from MATLAB code at the command line using the codegen function.

  1. Write two MATLAB functions, ep1 takes one input, a single scalar, and ep2 takes two inputs, both double scalars. In a local writable folder, create a MATLAB file, ep1.m, that contains:

    function y = ep1(u) %#codegen
y = u;
    In the same local writable folder, create a MATLAB file, ep2.m, that contains: 
    function y = ep2(u, v) %#codegen
y = u + v;

  2. Generate the C dynamic library.

    codegen -config:dll ep1 -args single(0) ep2 -args {0,0}

    On Microsoft Windows systems, codegen generates a C dynamic library, ep1.dll, and supporting files, in the default folder, codegen/dll/ep1. It generates the minimal set of #include statements for header files required by the selected code replacement library. On Linux, it generates a shared object (.so) file. On Mac, it generates a dynamic library (.dylib) file. The DLL linkage conforms to the target language, in this example, C. If you set the target language to C++, the linkage conforms to C++.

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