Structs

A scalar struct groups named fields into a single value. Each field can hold any type — scalar, matrix, string, complex, cell array, or another struct. Fields are stored in insertion order (MATLAB-compatible behaviour using an ordered map).

Creating structs

Field assignment

Assign to name.field to create the struct and set the field in one step:

pt.x = 3;
pt.y = 4;
pt.z = 0;

If the variable does not yet exist it is created as an empty struct and then the field is added. Assigning to a non-existent nested path creates all intermediate levels automatically:

car.engine.hp = 190;       % car and car.engine are both created here
car.dims.length_m = 4.76;

`struct()` constructor

Build a struct from key–value pairs:

s = struct('x', 1, 'y', 2)     % two fields
p = struct('name', 'Alice', 'score', 98.5)
e = struct()                    % empty struct (zero fields)

Arguments must come in pairs (name, value). The name must be a string ('single-quoted' or "double-quoted").

Reading fields

Use the same . notation:

pt.x          % 3
pt.y          % 4

car.engine.hp          % 190
car.dims.length_m      % 4.76

Chaining works to any depth. Accessing a field that does not exist is an error.

Built-in utilities

Function	Description
`fieldnames(s)`	Cell array of field names in insertion order
`isfield(s, 'x')`	`1` if field `'x'` exists, else `0`
`rmfield(s, 'x')`	Copy of `s` with field `'x'` removed; error if absent
`isstruct(v)`	`1` if `v` is a struct, else `0`

s.a = 1;  s.b = 2;  s.c = 3;

fn = fieldnames(s)       % {'a'; 'b'; 'c'}
fn{1}                    % a
numel(fn)                % 3

isfield(s, 'b')          % 1
isfield(s, 'z')          % 0

s2 = rmfield(s, 'b');
fieldnames(s2)           % {'a'; 'c'}

isstruct(s)              % 1
isstruct(42)             % 0

Display

s =

  struct with fields:

    x: 3
    y: 4
    engine: [1×1 struct]
    data: [1×100 double]

Nested structs and non-scalar values are shown inline as [1×1 struct], [M×N double], or {1×N cell}. Access the field directly to see its full contents.

Structs in functions

Pass and return structs like any other value:

function d = distance(pt)
  d = sqrt(pt.x^2 + pt.y^2 + pt.z^2);
end

p = struct('x', 1, 'y', 2, 'z', 2);
distance(p)    % 3

Build structs inside functions the same way:

function v = make_vec3(x, y, z)
  v.x = x;  v.y = y;  v.z = z;
end

u = make_vec3(1, 0, 0);
u.x    % 1

Nested structs

config.server.host = 'localhost';
config.server.port = 8080;
config.db.name     = 'prod';
config.db.timeout  = 30;

config.server.host    % localhost
config.db.timeout     % 30

fieldnames returns only the top-level fields:

fieldnames(config)    % {'server'; 'db'}

Workspace

Structs are not saved by ws / save — the same policy as matrices, complex values, and cell arrays.

who displays structs as:

s = [1×1 struct]

ccalc