Dynamic field names in MATLAB - Step-by-Step Execution

Concept Flow - Dynamic field names

Start

↓

Create struct

↓

Define field name as string

↓

Use dynamic field name to assign value

↓

Access or modify field using dynamic name

↓

End

This flow shows how to create a structure, define a field name as a string, and use that string to dynamically assign or access fields.

Execution Sample

MATLAB

fieldName = 'age';
person = struct();
person.(fieldName) = 30;
disp(person.age);

This code creates a struct and uses a dynamic field name to assign and display a value.

Execution Table

Step	Action	Variable/Field	Value	Output
1	Assign string to fieldName	fieldName	'age'
2	Create empty struct	person	struct with no fields
3	Assign 30 to person.(fieldName)	person.age	30
4	Display person.age	person.age	30	30
5	End of code

💡 Code ends after displaying the value of the dynamic field.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
fieldName	undefined	'age'	'age'	'age'	'age'
person	undefined	undefined	empty struct	struct with field 'age' = 30	struct with field 'age' = 30

Key Moments - 2 Insights

Why do we use parentheses and a dot like person.(fieldName) instead of person.fieldName?

Using person.(fieldName) tells MATLAB to use the value of the variable fieldName as the field name. person.fieldName would look for a field literally named 'fieldName', which does not exist. See execution_table step 3.

What happens if the field name string changes after assignment?

Changing the string variable after assigning the field does not change the existing field. The field name is fixed at assignment. See variable_tracker for fieldName and person after step 3.

Visual Quiz - 3 Questions

Look at the execution table at step 3. What field does person have after assignment?

A 'person'

B 'fieldName'

C 'age'

D No fields

💡 Hint

Check the 'Variable/Field' column at step 3 in the execution_table.

At which step is the value 30 assigned to the struct field?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Value' columns in the execution_table.

If we change fieldName to 'height' after step 3, what happens to person.age?

A person.age changes to person.height

B person.age remains 30

C person.age is deleted

D person becomes empty

💡 Hint

Refer to key_moments about field name changes after assignment.

Concept Snapshot

Dynamic field names in MATLAB:
- Use a string variable as a field name with syntax: structVar.(fieldName)
- Allows flexible field assignment/access
- Field name is fixed at assignment time
- Useful for loops or variable field names
- Example: person.(fieldName) = value;

Full Transcript

This example shows how to use dynamic field names in MATLAB structures. First, we assign the string 'age' to the variable fieldName. Then, we create an empty struct called person. Using dynamic field name syntax person.(fieldName), we assign the value 30 to the field named 'age'. Finally, we display the value of person.age, which outputs 30. The key point is that using parentheses with a variable allows MATLAB to use the variable's value as the field name, not the literal variable name. Changing the variable fieldName later does not affect the existing struct fields.