Date Formats and String Parsing — The Syntax Mess

Dates have a representation problem. The same calendar date — the fifth of April, 2024 — can be written as 04/05/2024, 05/04/2024, 2024-04-05, 05.04.2024, April 5, 2024, or 5 квітня 2024 р. These are not interchangeable. In the US, 04/05/2024 means April 5th. In Europe, it means May 4th. Feed the wrong format to a backend parser and you get a wrong date — sometimes an error, often not.

This module covers the full lifecycle of a date string: how it is written in a UI, how it travels over the network, how a server parser interprets it, and what can go wrong at each step. You will learn the ISO 8601 standard and why it is the only unambiguous option, how regional format ambiguity creates real production bugs, the difference between strict and lenient parsing, and the two failure modes — rejected input versus silently stored corruption — and why the second is far more dangerous.

After this module, you will know exactly what to test when a system accepts date strings from users, how to probe for parsing failures without access to source code, and how to verify that a system stores what it claims to accept.