MATLAB: Does mxCreateNumericArray returning NULL in the C code which uses libraries compiled using MATLAB Compiler SDK

MATLAB Compiler SDKmclinitializeapplicationmxcreatenumericarraynull

Hi,

I'm writing a Windows command line program to read an image from disk and then convert it into a mxArray suitable for calling a MATLAB compiled library. I'm having an issue with mxCreateNumericArray. It is not allocating the array and returning NULL instead. See attached sample code.

Is there something I need to do in a command line program to initialize the libmat library?

Best Answer

The reason why mxCreateNumericArray returns NULL is because MCR is not initialized in Windows application C code.

In order to make it work, call the 'mclInitializeApplication' routine. Make sure that the application was initialized properly by checking the return status.

This initialization has to be done before calling any MATLAB APIs or MATLAB Compiler SDK generated shared library functions.

if( !mclInitializeApplication(NULL,0) )
    {
        fprintf(stderr, "Could not initialize the application.\n");
        return -1;
    }

The following document explains step-by-step guide to integrate a C shared library into a Windows Application-

https://www.mathworks.com/help/compiler_sdk/cxx/integrate-a-c-shared-library-into-an-application.html

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MATLAB: What is the difference between functions like mclmcrInitialize and mclInitializeApplication

mclmcrInitialize and mclInitializeApplication are MATLAB Compiler Runtime (MCR) functions which are typically used in driver applications for shared libraries.

mclInitializeApplication: This function should be called once at the beginning of your driver application. You must make this call before calling any other MathWorks functions.

mclmcrInitialize: Loads three main libraries (libmex,libmat.libmclmcr) and sets runtime environment for running MATLAB functions.

If the driver application has a main() method, you need to use mclInitializeApplication in the main() method. This in turn calls mclmcrInitialize to load all the libraries.

For example, refer to the following C shared library example:

https://in.mathworks.com/help/compiler_sdk/cxx/c-shared-library-target.html?s_tid=srchtitle

If the driver application has a main() as well as an additional method which uses the mclRunMain function, you must first call mclmcrInitialize. Then inside the function called from mclRunMain, you can call mclInitializeApplication to complete the MCR initialization procedure. mclRunMain is an additional MCR function which handles platform specific threading issues.

For example, refer to the following C++ shared library example:

https://in.mathworks.com/help/compiler_sdk/cxx/c-shared-library-target-1.html?s_tid=srchtitle

In this example, run_main() is the additional method which is called by the mclRunMain function.

MATLAB: How to use the mclInitializeApplication function to make a C-shared library that does not use the JVM or JIT in MATLAB 7.0 (R14)

The C/C++ shared libraries created with the MATLAB Compiler can be run in "nojvm" and/or "nojit" mode.

This is accomplished through the use of the mclInitializeApplication function. The function signatures for this function is as follows:

 bool mclInitializeApplication(const char **options, int count);

In other words, mclInitializeApplication takes an array of strings of user-settable options and a count of the number of options (the length of the option array). This function returns true (1) for success and false (0) for failure.

To specify that the library should not use the Java Virtual Machine, the option string is "nojvm". To specify that the library should not use the JIT, use the option string "nojit" .

The use of these options is illustrated in the following example, where a MATLAB-generated library named "hello" is called.

 #include "hello.h"
 #include <stdio.h>
 int main()
 {
     char *pStrings[]={"-nojvm","-nojit"};
     if (!mclInitializeApplication(pStrings,2))
     {
         fprintf(stderr, "Could not initialize MCR for the application.\n");
         return -1;
     }
     if(!helloInitialize())
     {
         fprintf(stderr, "Could not initialize the library.\n");
         return -1;
     }
     mlfHello();
     helloTerminate();
     mclTerminateApplication();
     return 0;
 }

For more information about calling a MATLAB-generated shared library, see the "C Shared Library Example" section of the MATLAB Compiler SDK documentation:

http://www.mathworks.com/help/releases/R2016b/compiler_sdk/cxx/c-shared-library-target.html#f2-1000836

Best Answer

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MATLAB: What is the difference between functions like mclmcrInitialize and mclInitial​izeApplica​tion

MATLAB: How to use the mclInitializeApplication function to make a C-shared library that does not use the JVM or JIT in MATLAB 7.0 (R14)

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MATLAB: What is the difference between functions like mclmcrInitialize and mclInitializeApplication