Integrating MATLAB and Visual Studio using Engine API

Tutorial 2 : Writing Engine scripts.

After having set Visual Studio to be integrated with MATLAB, you need to add some fragments of code along with your C/C++ program to call or send values to MATLAB.

Everything you need will be contained in the libraries engine.h and matrix.h

Every engine application will have a pointer of data type Engine that defines an engine session. We will be using variable addresses to copy values using pointers and using in either MATLAB or C or both.

Opening and closing engine sessions :

Following functions will be needed for its working :

• ep = engOpen() - where engine session starts. ep of type for MATLAB Engine.
• engClose(ep) - closes engine session defined by pointer ep

On Windows system, engOpen() will have argument "NULL"

Pointers to store values for transferring between MATLAB and C :

Remember, for transferring arrays and values with MATLAB, we need to have an intermediate data-type, mxArray. Creates MATLAB arrays.

Define pointers of mxArray data-type as an array using, mxCreateDoubleMatrix, mxCreateNumericMatrix, etc. (See documentation for further types and its arguments)

For example, mxArray *array = mxCreateDoubleMatrix(5,3,mxREAL); 

creates a pointer to a double matrix with 5 rows and 3 columns and has elements belonging to Real Numbers.

Performing the actual putting,getting and evaluation of values in MATLAB workspace :

Following functions might be used to get or put value in mxArray variables from/into MATLAB workspace :

• engEvalString(ep,"MATLAB code") - Puts whatever written in string to MATLAB workspace opened by ep Engine session pointer.
• engPutVariable(ep,"MATLAB variable",mxArray pointer) - Puts values from an address in C space to an address in MATLAB workspace.
• mxArray pointer = engGetVariable(ep,"MATLAB variable") - Gets values from MATLAB workspace variable specified in " " and is stored in mxArray pointers.
• mxGetPr(mxArray pointer) - Gets the starting address of the first real element of pointer.

We know how to start engine, how to make MATLAB array pointers, how to run commands on MATLAB workspace, how to put and get values in MATLAB array pointers from workspace but we still have the gap between MATLAB and C; to get values from mxArray pointers to int/double/etc. data type variables in C we use 

memcpy(address of destination,address of source,number of bytes to be copied)

Use (void *) , also called General Purpose Pointer as it can be used as any data-type pointer.

Moreover, along with engOpen you can add error messages with it.(Refer Documentation of MATLAB)

engwindemo.c is a good example to learn from. Below will be the screenshots of my code, describing stages of Engine session. For full code, you can visit my github repo HERE

Initialize Engine session and define MATLAB array pointers.

Sending commands to MATLAB workspace

Getting values from MATLAB workspace

Closing engine session