28 September 2022 Qlik subroutine parameters – passing arguments by reference and by value Share this message Every Friday at Bitmetric we’re posting a new Qlik certification practice question to our LinkedIn company page. Last Friday we asked the following Qlik Data Architect certification practice question about passing arguments to Qlik subroutine parameters: This proved to be a harder question than expected, as only a single person got the right answer. Well done Vaibhav Sharma! The correct answer is B: lines 4 and 8 both show the value 8 We’re modifying the parameter called pInput and somehow this also affects the variable vNumber? How is that possible? The explanation is that we passed the argument by reference instead of by value. In short, when we pass by value we provide a copy of the variable, but when we pass by reference we provide the actual variable to the subroutine. Read on to get a more in-depth explanation. Sidebar: argument vs parameterThese terms are often used interchangeably, but they actually do have different meanings. A parameter is the name that is listed in the subroutine definition. In this example that’s pInput. An argument is the value that’s actually supplied. In this example that’s vNumber. How variables are stored in memory To explain the difference between passing by value and passing by reference we first need some basic knowledge of how memory works. We’ll use a simplified explanation for this, which should be enough to understand the basic concept. You can consider memory as a collection of blocks that can hold data. Each block has an address, numbers 1 through 60in the illustration below. When you store a value into a variable, your operating system will automatically decide where to place this in memory. In the illustration below, the value we’ve set for the vNumber variable is stored at memory address 32. Pass by value When we pass by value, the value is copied to another location in memory. In the illustration below a copy of the value is placed at memory address 24. Subsequent operations, such as the multiplication in the subroutine, are performed on the copy. The original value is left untouched. Pass by reference When we pass by reference, we pass a reference to the memory address of the variable. What this means in our example is that both vNumber and vInput now reference the same memory space and value within that space. Any operation that is performed to pInput updates the same value that is being referenced by vNumber, and vice versa. This explains the behavior that we see in the example script. Passing by value vs passing by reference in Qlik So how can we fix this script to ensure that vNumber is passed by value? By using Dollar-sign expansion! This passes the value of the variable to the subroutine, rather than a reference to the variable. See the updated script below, with a change on line 9. That’s it for this week. See you next Friday? More from the Bitmetric team Qlik Cloud Backup Protect your investment in Qlik with daily incremental backups stored in an encrypted environment with redundant storage. Available for as little as 2 Euro per day. Learn more. Masters Summit for Qlik The Masters Summit for Qlik provides the next step in your path to becoming a Qlik specialist. As an extra perk, Bitmetric has secured an over $450 discount just for you! Use code BITMETRIC at checkout. Read more here. Friday Qlik Test Prep Script Solution How can we help? Barry has over 20 years experience as a Data & Analytics architect, developer, trainer and author. He will gladly help you with any questions you may have. Call us Mail us 13 June 2025 Qlik Extension: Scroll to Object Ever since Qlik introduced extended sheets in June 2018, we at Bitmetric have been fans. The ability to extend a sheet vertically and add visualizations below the fold is a powerful way to present more insights without cluttering the main view. Yet, even after seven years, it still feels like a hidden feature. Many users […] Extension Qlik 2 June 2025 Simplifying Data Integration with TimeXtender At Bitmetric, we believe in making technology work for people, not the other way around. TimeXtender’s approach to data integration fits this philosophy by removing obstacles and giving users practical tools to manage their data. Solution TimeXtender 12 May 2025 Dagelijkse Qlik Ondersteuning: altijd hulp bij data analyse Bij Bitmetric snappen we hoe belangrijk het is dat je Qlik omgeving gewoon goed werkt. Of je nu dagelijks data analyseert of snel wat inzichten nodig hebt, je wilt dat alles soepel verloopt. Daarom staan onze experts elke dag voor je klaar. Van kleine vragen tot ingewikkelde uitdagingen, we helpen je graag verder, zodat jij je kunt focussen op wat echt telt! Qlik
13 June 2025 Qlik Extension: Scroll to Object Ever since Qlik introduced extended sheets in June 2018, we at Bitmetric have been fans. The ability to extend a sheet vertically and add visualizations below the fold is a powerful way to present more insights without cluttering the main view. Yet, even after seven years, it still feels like a hidden feature. Many users […] Extension Qlik
2 June 2025 Simplifying Data Integration with TimeXtender At Bitmetric, we believe in making technology work for people, not the other way around. TimeXtender’s approach to data integration fits this philosophy by removing obstacles and giving users practical tools to manage their data. Solution TimeXtender
12 May 2025 Dagelijkse Qlik Ondersteuning: altijd hulp bij data analyse Bij Bitmetric snappen we hoe belangrijk het is dat je Qlik omgeving gewoon goed werkt. Of je nu dagelijks data analyseert of snel wat inzichten nodig hebt, je wilt dat alles soepel verloopt. Daarom staan onze experts elke dag voor je klaar. Van kleine vragen tot ingewikkelde uitdagingen, we helpen je graag verder, zodat jij je kunt focussen op wat echt telt! Qlik