# Setting a dynamic element size in a flat structure

Use a SetElementProperty to define the size of an element based on the value of another element in a flat file.

## Before you begin

You have a flat file to use as sample document. You can create one from the sample data provided below.

## About this task

In this example, you have a flat file containing three elements named a, b and c. The a element is an integer that defines the size of the b element. Since this size can vary, you cannot set a fixed size in the b element properties. However, you still need to define its size to indicate where the b element ends and the c element starts.

You can use the following data for your sample input:

```
03bbbcc
```

## Procedure

1. Create your structure:
   1. In the Hierarchical Mapper, right-click Structures and click New > Structure.
   2. In the wizard that opens, select Create a new structure where you manually enter elements and click Next.
   3. Select a folder and enter a name for your structure, then click Next.
   4. Select the Flat Files representation and click Next.
   5. Click Import a file as document and click Next.
   6. Browse to the relevant folder and select your flat file, then click Finish.
2. Right-click the section on the left of your workspace and click New Element to create a root element.
3. Right-click the root element and create three child elements named a, b and c.

   Your structure looks like this: ![Structure result.](https://help.qlik.com/talend/en-US/data-mapper-functions-reference-guide/Resources/images/set_dynamic_size_01_structure.png)
4. Click the a element and enter 2 in both Size Min/Max fields, then select Integer (32) in the Data Type drop-down list.

   This indicates that the a element is an integer with a fixed size of two bytes. When clicking this element in the structure, 03 is highlighted in the Document tab.
5. Click the c element and enter 2 in both Size Min/Max fields.

   These properties define a fixed size for the c element, however it is not highlighted in the Document tab because there is no information specifying where the b element ends and the c element starts. ![Elements' properties.](https://help.qlik.com/talend/en-US/data-mapper-functions-reference-guide/Resources/images/set_dynamic_size_02_c_element.png)
6. Click the b element and place a SetElementProperty in its Util tab.
7. Double-click the SetElementProperty and select Number of bytes in the Property drop-down list, then click OK.
8. Place the a element on the Value argument.

   This indicates that the size of the b element is equal to the value of the a element. ![Placement of a element.](https://help.qlik.com/talend/en-US/data-mapper-functions-reference-guide/Resources/images/set_dynamic_size_03_setelementproperty.png)

## Results

Your structure is now configured, when clicking the b element, the value bbb is highlighted in the Document tab, and cc is highlighted when clicking the c element. ![Structure result.](https://help.qlik.com/talend/en-US/data-mapper-functions-reference-guide/Resources/images/set_dynamic_size_04_result.png)