MAT_VARCREATESTRUCT2(3) Library Functions Manual MAT_VARCREATESTRUCT2(3)

Mat_VarCreateStruct2 — Creates a structure variable.

#include <matio.h>

matvar_t *
Mat_VarCreateStruct(const char *name, int rank, const size_t *dims, const char *const *fields);

The () function creates a structure variable named name that can be written to a MAT file.

If the structure variable was successfully created, a pointer to the variable is returned. Otherwise NULL is returned. The structure variable pointer should be free'd when no longer needed using Mat_VarFree(). The names of the fields are copied in the function, and thus should be released after calling the function if necessary. The names of the fields has to be a NULL-terminated array.

This example program opens a MAT file named by the first argument to the program, and writes a structure named to the file.

#include "matio.h"

int
main(int argc, char **argv)
{
    mat_t    *matfp;
    matvar_t *matvar;
    matvar_t *field;
    const char *fields[3] = {"field1", "field2", NULL};
    double       data1 = 1, data2 = 2;
    size_t       dims[2] = {1, 1};

    matfp = Mat_Open(argv[1], MAT_ACC_RDWR);
    if ( NULL == matfp ) {
        fprintf(stderr, "Error opening MAT file %s0, argv[1]);
        return EXIT_FAILURE;
    }

    dims[0] = 1; dims[1] = 1;
    matvar = Mat_VarCreateStruct2("a", 2, dims, fields);
    if ( NULL == matvar ) {
        Mat_Close(matfp);
        return EXIT_FAILURE;
    }

    field = Mat_VarCreate(NULL, MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, &data1,
                MAT_F_DONT_COPY_DATA);
    Mat_VarSetStructFieldByName(matvar, "field1", 0, field);

    field = Mat_VarCreate(NULL, MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, &data2,
                MAT_F_DONT_COPY_DATA);
    Mat_VarSetStructFieldByName(matvar, "field2", 0, field);

    Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_NONE);
    Mat_VarFree(matvar);

    Mat_Close(matfp);
    return EXIT_SUCCESS;
}

Mat_VarCreate(3), Mat_VarSetStructFieldByName(3)

January 5, 2026 Linux 6.18.3-arch1-1