No, COBOL does not inherently default to 1875-05-20 for corrupt or missing dates. The appearance of this specific date likely stems from particular implementations or custom error handling within specific COBOL systems. The language itself doesn't prescribe this default. Instead, how COBOL handles invalid dates depends on the compiler, runtime environment, and how the program was written. A program might display a default value, a blank date, or trigger an error message, among other possibilities. The 1875-05-20 date is potentially an arbitrary choice made by a programmer or a consequence of how a specific system interprets corrupted data.
The Stack Exchange post explores the persistent rumor that COBOL systems default to the date May 20, 1875, when encountering invalid or missing date data. The original poster clarifies that they are not seeking information about specific implementations or why this specific date might be chosen, but rather whether such a default behavior was ever a standard practice or a commonly encountered quirk within COBOL itself.
The primary answer delves into the history and mechanics of date handling within COBOL, highlighting the fact that the language itself does not prescribe a specific default date. Instead, date handling is largely left to the implementation and the individual program's design. The answer emphasizes that early COBOL compilers and runtime environments had limited error handling capabilities. Consequently, unexpected or corrupt date data might lead to unpredictable behavior, including potentially displaying a seemingly arbitrary date. However, this date would be a consequence of the specific system's internal workings rather than a standardized COBOL feature.
The answer further explains that the prevalent use of two-digit years in older COBOL systems contributed to the "Year 2000" (Y2K) problem, but this is distinct from the question of a default date for corrupted data. The Y2K issue stemmed from ambiguity in interpreting two-digit year values, whereas the question at hand focuses on how systems handled entirely missing or invalid date information. The answer concludes that while a specific default date like May 20, 1875, is unlikely to be a COBOL standard, the appearance of arbitrary dates due to data corruption and limited error handling was a plausible scenario in older systems.
Summary of Comments ( 292 )
https://news.ycombinator.com/item?id=43073149
Hacker News users discuss various potential reasons for the 1875-05-20 default date in COBOL, with speculation centering around it being an arbitrary "filler" value chosen by programmers or a remnant of test data. Some commenters suggest it might relate to specific COBOL implementations or be a misinterpretation of a different default behavior, like zeroing out the date field. Others offer alternative explanations, proposing it could represent the earliest representable date in a particular system or stem from a known data corruption issue. A few emphasize the importance of context and specific COBOL versions, noting that the behavior isn't a universal standard. The overall tone suggests the specific date's origin is uncertain and likely varies depending on the system in question.
The Hacker News post titled "Does or did COBOL default to 1875-05-20 for corrupt or missing dates?" has several comments discussing the quirks of COBOL date handling.
One commenter shares an anecdote about encountering a similar issue with a COBOL system at a bank in the 1990s. The system used a default date of 1900-01-01 for bad dates, leading to incorrect interest calculations and frustrated customers. This personal experience adds weight to the idea of default dates causing real-world problems in COBOL systems.
Another commenter clarifies that COBOL itself doesn't have a built-in default date. Instead, the specific behavior depends entirely on how the individual program was written. They explain that the default date would be whatever the programmer coded it to be, or potentially a system-level default set by the operating system or runtime environment. This highlights the importance of understanding the specific implementation details of a COBOL system rather than assuming universal behavior.
Expanding on the programming aspect, a subsequent comment mentions the common practice of using
LOW-VALUESas a placeholder for missing or invalid dates.LOW-VALUESis not a specific date, but rather a special value representing the lowest possible value for a data field. This points to a common technique used by COBOL programmers to handle data integrity issues.One comment humorously suggests the possibility of the 1875-05-20 date being a programmer's birthday or another significant date, but acknowledges this is pure speculation. This adds a touch of levity to the discussion while hinting at the mysteries that can lurk within legacy code.
Another commenter, with apparent experience in COBOL systems, questions the validity of the 1875 date. They point out the relative recency of COBOL compared to that date, suggesting it's unlikely to be a genuine default. They posit that it's more probable the date arose from a specific data corruption incident rather than a deliberate design choice.
Finally, a comment discusses how default dates in older systems could sometimes reflect the earliest date representable in a given data format. This offers a technical explanation for how unusual default dates might arise, even without explicit programmer intervention. They explain how systems relying on two-digit year representations could end up interpreting "00" as 1900 or even 1800.
In summary, the comments paint a picture of COBOL date handling as being highly dependent on specific implementations. While COBOL itself doesn't dictate a default date, a variety of practices and potential errors could lead to unexpected results. The discussion moves from personal anecdotes and speculation to more technical explanations of how and why unusual default dates might appear in these systems.