MATLAB: Is it possible to open a compressed MAT file using matOpen in C

apimatMATLABmatopen

Best Answer

'matOpen' and the rest of the MAT API are capable of reading a MAT file stored with the compression provided by the MAT library (E.g. save -v7.3).

In the MATLAB code be sure to include the below line:

>> save filename.mat -v7.3;

In C code you can use the below lines:

#include "mat.h"
MATFile *matOpen(const char *filename, const char *mode);

Related Solutions

MATLAB: How to deal with sym data type in C mex file

Operating on "syms" requires going through the MATLAB code provided with the Symbolic Math Toolbox,

whether from MATLAB or MEX files.

Within MEX files, this can be done by calling mexCallMATLAB.

Below is a small example that we hope will be able to convey you the idea.

Please refer to the MEX API for memory management and other details regarding the implementation.

//=====================================================================

// mexCallSym.c

// example for illustrating how to use mexCallMATLAB

// This file creates a symbolic variable x, creates the symbolic

// expression ellipticE(x) and then integrates it with respect to x.

// The result is returned.

// This is a MEX-file for MATLAB.

//===================================================================*/

#include "mex.h"

//gateway function//

void mexFunction(

int nlhs,

mxArray* plhs[],

int nrhs,

const mxArray* prhs[]){

mxArray* xstr[1];

mxArray* x[1];

mxArray* f_x[1];

mxArray* int_args[2];

if (nlhs > 1) {

mexErrMsgIdAndTxt("MATLAB:maxlhs", "Too many outputs");

}

if (nlhs < 1) {

mexErrMsgIdAndTxt("MATLAB:minlhs", "Too few outputs");

}

// Remark: we may want to also ensure we didn't get parameters.

// (Ignoring here for brevity.)

(void) nrhs; //unused//

(void) prhs; //unused//

// create symbolic variable x

xstr[0] = mxCreateString("x");

mexCallMATLAB(1, x, 1, xstr, "sym");

mxDestroyArray(xstr[0]);

// create symbolic expression ellipticE(x)

mexCallMATLAB(1, f_x, 1, x, "ellipticE");

// integrate f_x with respect to x

int_args[0] = f_x[0];

int_args[1] = x[0];

mexCallMATLAB(1, plhs, 2, int_args, "int");

// cleanup allocated memory

mxDestroyArray(x[0]);

mxDestroyArray(f_x[0]);

// Note: int_args does not point to additional allocations

// and should not be freed

}

In order to verify, please save the above function in the current directory and verify with the following:

>> mex mexCallSym.c

>> t = mexCallSym

t =

(2*ellipticE(x))/3 - (2*ellipticK(x))/3 + x*((2*ellipticE(x))/3 + (2*ellipticK(x))/3)

MATLAB: Do I get Access Violation Error while deleting arrays using mxdestroyarray to cleanup memory

The reason why the struct fields are empty and there are Access Violation Exception in the code is because you are freeing same memory twice.

mxdestroyarray deallocates the memory occupied by the specified _mxArray_ including Fields of structure arrays as well.

So, when you deallocate memory occupied by struct pointer _strp_-

mxDestroyArray(strp);

It not only deallocates memory occupied by _strp_, but also _mp1_ and _mp2_.

And, calling _mxDestroyArray_ for those _mxArray_ will cause Access Violation.

mxDestroyArray(mp1);
mxDestroyArray(mp2);

Moreover, if you clear memory used by mp1 and mp2, before writing data to MAT file using _matPutVariable_, it will write empty field values as the memory has already been destroyed-

mxDestroyArray(mp1);
mxDestroyArray(mp2);
matPutVariable(fp, matTName, strp);

The <https://www.mathworks.com/help/matlab/apiref/mxdestroyarray.html mxdestroyarray> document explains this-

mxDestroyArray deallocates the memory occupied by the specified mxArray including: * Characteristics fields of the mxArray, such as size (m and n) and type. * Associated data arrays, such as pr and pi for complex arrays, and ir and jc for sparse arrays. * Fields of structure arrays. * Cells of cell arrays.

Moreover, it is specified in the <https://www.mathworks.com/help/matlab/apiref/mxsetfieldbynumber.html mxsetfieldbynumber> and <https://www.mathworks.com/help/matlab/apiref/mxsetfield.html mxsetfield> doc pages not to deallocate memory for struct values.

To free memory for structures created using this function, call mxDestroyArray only on the structure array. Do not call mxDestroyArray on the array pvalue points to. If you do, then MATLAB attempts to free the same memory twice, which can corrupt memory.

You can verify that ny removing mxDestroyArray() on mp1 and mp2.

It will fix the issue and you will successfully write struct data to MAT file using both _*mxSetField*_ and _*mxsetfieldbynumber.*_

Hope this helps!

Best Answer

Related Solutions

MATLAB: ​How to deal with sym data type in C mex file

MATLAB: Do I get Access Violation Error while deleting arrays using mxdestroyarray to cleanup memory

Related Question

MATLAB: How to deal with sym data type in C mex file