Using the C++ Math Library

Creating Structures

The MATLAB C++ Math Library allows you to create structures by:

• Using a structure creation routine
• Using a structure conversion routine
• Assigning a value to an element in a structure.

Using a Structure Creation Routine

You can create a structure using the struct_func() routine. This routine lets you define the fields in the structure and assign a value to each field. For example, the following code fragment creates a structure that contains two fields, a text string and a scalar value.

mwArray A;

A = struct_func("name",   // field name
                "John",   // value
                "number", // field name
                 311);    // value

cout << A << endl;

This code produces the following output:

  name: 'John'
number: 311

Note    The struct_func() routine defines the fields and their values in a single instance of a structure. To create an array of structures, use MATLAB indexing syntax in the assignment statement, as described in Using Assignment to Create Structures.

Using a Structure Conversion Routine

You can also create structures by converting an existing MATLAB cell array into a structure, using the cell2struct() routine. When converting a cell array into a structure, you must create a separate cell array that contains the names you want to assign to fields in the structure.

The following code fragment creates a cell array, C, containing data and a second cell array, F, containing field names. The example then passes these cell arrays to cell2Struct().

mwArray C,F,S;

// create cell array to be converted

C = cellhcat("tree",
               37.4,
             "birch");

cout << C << endl;

// create cell array of field names 

F = cellhcat("category",
             "height",
             "name");

// convert cell array to structure 

S = cell2struct(C,F,2);

cout << S << endl;

This code generates the following output:

'tree'   [37.4000]    'birch'

category: 'tree'
  height: 37.4000
    name: 'birch'

Using Assignment to Create Structures

As with other MATLAB arrays, if you assign values to fields in a structure that is in an array of structures, the MATLAB C++ Math Library creates an array of structures large enough to accommodate the location specified by the index string.

The following example defines a structure with two fields, name and number. Because it is an indexed assignment statement, the library creates an array of 3 of these structures, assigning values to the third structure in the array. The first two structures in the array are initialized to contain empty arrays for each field. This C++ code is equivalent to the MATLAB statement,
S(2) = struct('name','jim','number',312).

mwArray S;

// Create array of structures by assignment

S(3) = struct_func("Name",    // Field name
                   "Jim",     // Value
                   "Number",  // Field name
                    312);     // Value

cout << S << endl;

This code generates the following output:

1x3 struct array with fields
    Name
    Number

For more detailed information about using indexing, see Chapter 4.

MATLAB Structures

Performing Common Array Programming Tasks