CLAD Software Development Best Practices 5 — Questions and Answers
Question 1: What LabVIEW best practice ensures that resources like file references and DAQmx tasks are always properly closed?
- Closing them manually at the end of the main VI only
- Using error clusters to propagate past the close node without wiring it
- Placing close/stop calls inside the error handler and in the normal exit path, or using 'Close' in a finally-style structure (Correct answer)
- Relying on LabVIEW garbage collection to close them automatically
Correct answer: Placing close/stop calls inside the error handler and in the normal exit path, or using 'Close' in a finally-style structure
Resources must be explicitly closed on both the normal and error paths; LabVIEW does not automatically release references when a VI stops.
Question 2: Which approach best supports unit testing of LabVIEW subVIs?
- Running the entire application and checking the final output
- Using the NI Unit Test Framework to create test cases that call individual subVIs with known inputs (Correct answer)
- Manually inspecting the block diagram for logic errors
- Testing only the top-level VI and assuming subVIs are correct
Correct answer: Using the NI Unit Test Framework to create test cases that call individual subVIs with known inputs
The NI Unit Test Framework enables automated, isolated testing of individual subVIs, making bugs easier to locate.
Question 3: When should you use LabVIEW's 'Disable Structure' during development?
- To permanently remove code from the application
- To temporarily exclude code from execution without deleting it, useful for debugging (Correct answer)
- To prevent users from modifying the front panel
- To disable error handling in a specific section
Correct answer: To temporarily exclude code from execution without deleting it, useful for debugging
A Disable Structure lets you exclude code from compilation temporarily while keeping it on the diagram for later re-enabling.
Question 4: What is the recommended way to share data between iterations of a loop in LabVIEW?
- Global variables
- Local variables declared inside the loop
- Shift registers on the loop structure (Correct answer)
- Property nodes on front panel controls
Correct answer: Shift registers on the loop structure
Shift registers are the idiomatic LabVIEW mechanism for carrying values from one loop iteration to the next.
Question 5: Which LabVIEW practice improves front panel usability for end users?
- Placing all controls in alphabetical order regardless of workflow
- Grouping related controls visually, adding clear labels, and using appropriate control styles for the data type (Correct answer)
- Using only numeric controls for all input types
- Hiding the front panel entirely in deployed applications
Correct answer: Grouping related controls visually, adding clear labels, and using appropriate control styles for the data type
Organizing controls logically, labeling them clearly, and matching control style to data type reduces user errors and training time.
Question 6: In LabVIEW, which pattern is best suited for an application that must respond to multiple asynchronous events such as button clicks, timer ticks, and incoming data?
- A flat sequence structure with polling
- An Event Structure inside a while loop (Correct answer)
- Multiple nested while loops
- A single case structure executed once
Correct answer: An Event Structure inside a while loop
An Event Structure inside a while loop efficiently waits for and dispatches multiple event types without consuming CPU through polling.
Question 7: What is the purpose of the LabVIEW 'connector pane' on a subVI?
- It defines the VI's icon appearance on the block diagram
- It specifies which front panel terminals are exposed as inputs and outputs when the VI is used as a subVI (Correct answer)
- It controls how error clusters are displayed
- It sets the VI's execution priority
Correct answer: It specifies which front panel terminals are exposed as inputs and outputs when the VI is used as a subVI
The connector pane maps front panel controls and indicators to input/output terminals so the subVI can be wired in a calling VI's block diagram.
CLAD Software Development Best Practices 5
What LabVIEW best practice ensures that resources like file references and DAQmx tasks are always properly closed?