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.\" Copyright (c) 2015-2025, The matio contributors
.\" Copyright (c) 2012-2014, Christopher C. Hulbert
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright notice, this
.\" list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright notice,
.\" this list of conditions and the following disclaimer in the documentation
.\" and/or other materials provided with the distribution.
.\"
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.\" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
.\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd October 26, 2025
.Dt MAT_VARCREATE 3
.Os
.Sh NAME
.Nm Mat_VarCreate
.Nd Creates a MAT variable structure.
.Sh SYNOPSIS
.Fd #include <matio.h>
.Ft matvar_t *
.Fo Mat_VarCreate
.Fa "const char *name"
.Fa "enum matio_classes class_type"
.Fa "enum matio_types data_type"
.Fa "int rank"
.Fa "const size_t *dims"
.Fa "const void *data"
.Fa "int opt"
.Fc
.Sh DESCRIPTION
The
.Fn Mat_VarCreate
function creates a MAT structure variable named
.Fa name
that can be written to a MAT file.
The
.Fa class_type
argument specifies the class of the variable, and the
.Fa data_type
argument specifies the type of the data.
For example, a double-precision class would use
.Dv MAT_C_DOUBLE
for the class type and
.Dv MAT_T_DOUBLE
for the data type.
In some instances, the data type may not match the class type.
For example, an array of integers can be written in the double-precision
class by using
.Dv MAT_T_INT32
for
.Fa data_type.
.Pp
The
.Fa rank
argument specifies how many dimensions the data has.
The number of elements in each dimension is specified in the array
.Fa dims.
.Pp
The
.Fa data
argument is a pointer to the variable data.
The pointer is typically a pointer to a numeric array (e.g. double, float, int,
etc.) for real variables.
For complex variables, the pointer is a pointer to a
.Vt mat_complex_split_t
which contains pointers to the real and imaginary data as fields of the
structure.
For sparse variables, the pointer should be a
.Vt mat_sparse_t *.
.Sh RETURN VALUES
If the variable was successfully created, a pointer to the variable is returned.
Otherwise NULL is returned.
The variable should be free'd when no longer needed
using
.Fn Mat_VarFree .
.Sh EXAMPLES
The example program below creates a MAT file named
.Va test.mat,
and writes two real numeric variables
.Va x
and
.Va y
and a complex variable
.Va z
to the file.
.Bd -literal
#include <stdlib.h>
#include <stdio.h>
#include "matio.h"
int
main(int argc,char **argv)
{
mat_t *matfp;
matvar_t *matvar;
size_t dims[2] = {10,1};
double x[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9,10},
y[10] = {11,12,13,14,15,16,17,18,19,20};
struct mat_complex_split_t z = {x, y};
matfp = Mat_CreateVer("test.mat", NULL, MAT_FT_DEFAULT);
if ( NULL == matfp ) {
fprintf(stderr, "Error creating MAT file \"test.mat\"\n");
return EXIT_FAILURE;
}
matvar = Mat_VarCreate("x", MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, x, 0);
if ( NULL == matvar ) {
fprintf(stderr, "Error creating variable for 'x'\n");
} else {
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_NONE);
Mat_VarFree(matvar);
}
matvar = Mat_VarCreate("y", MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, y, 0);
if ( NULL == matvar ) {
fprintf(stderr, "Error creating variable for 'y'\n");
} else {
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_NONE);
Mat_VarFree(matvar);
}
matvar = Mat_VarCreate("z", MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, &z,
MAT_F_COMPLEX);
if ( NULL == matvar ) {
fprintf(stderr, "Error creating variable for 'z'\n");
} else {
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_NONE);
Mat_VarFree(matvar);
}
Mat_Close(matfp);
return EXIT_SUCCESS;
}
.Ed
.Sh SEE ALSO
.Xr Mat_VarCreateStruct 3 ,
.Xr Mat_VarFree 3 ,
.Xr Mat_VarWrite 3
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