Fencepost Error

Why Trust Techopedia

What Does Fencepost Error Mean?

A fencepost error is a specific type of off-by-one error that has to do with unlikely or misunderstood algorithms for development.

Advertisements

Fencepost errors are also known as telegraph pole errors and lamppost errors.

Techopedia Explains Fencepost Error

At the heart of the fencepost error is the idea that the number of posts used for a fence project differs based on whether the fence is long with two opposite ends, or whether it circles back to a closed loop. In the former scenario, a fencepost error can occur if a person makes an intuitive supposition that a fence only needs as many posts as dividing the length by the length between posts. For example, if the fence is 50 feet long and has posts every 5 feet, the human working on this problem might suppose that the fence needs 10 posts. However, if the fence is not a closed loop, it needs an additional post at the end — in other words, it needs a post at the starting point or zero, as well as a post at the ending point or end number. Algorithms demonstrating the fencepost principle would use a phrase like “n+1” posts. However, it must be noted that if the fence is a closed loop, the additional fencepost is not needed.

The fencepost error has multiple allegories and applications to coding and development. It represents one of many logical errors that cause programs to experience bugs or produce inaccurate results.

Advertisements

Related Terms

Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.