The “C” programming language is one of the most popular computer languages in the history of computing. The Y2038 issue originated in “C”, while it was being developed along with UNIX. The ‘heart’ of the Y2038 issue is the representation of time in seconds as a 32-bit integer (usually via a variable of type time_t). “time_t” is usually a 32-bit signed integer on 32-bit systems, and 64-bit signed integer on 64-bit systems. The epoch is usually midnight on Jan 1, 1970. The maximum number of seconds that can be represented in a 32-bit quantity will be exceeded after Jan 19, 2038 at 3:14:07 GMT.

One very appealing aspect of “C” is that it gives programmers absolute power and flexibility, but of course this also means that even small programming errors or bad assumptions can cause unintended consequences. As one example, any variable in “C” can be cast to another type, either implicitly or explicitly. If a cast is implicit (and there is a loss of precision), the compiler will at least print a warning. If a cast is explicit, the compiler may not even print a warning. As a case in point, if a programmer writing code on a 64-bit platform explicitly casts a variable of type time_t to another variable which happens to be a 32-bit signed integer, nothing bad may happen until the Y2038 rollover. After that time, what happens will depend on the program, but generally it won’t be good!

When faced with the task of finding and addressing Y2038 in “C” code, one approach is to search for all time-related functions. However, the usage of time in “C” is a fairly complex subject. There are numerous API functions, data structures, data types, and environment variables related to time. Even though “C” is standardized, significant differences do exist between implementations on different platforms. Each platform’s implementation can also evolve over time.

The table below is an attempt to list all API functions, data structures, data types, and environment variables having to do with time for some of the most popular platforms, including Linux, Microsoft Windows, Apple OSX, and VxWorks. Columns are also included for ISO and POSIX standards. As there are multiple versions of ISO and POSIX standards, the columns provided generally reflect the most recent versions. (This table is an ongoing work in progress. Over time, we plan to include additional platforms and additional links to external references (e.g. MSDN pages, etc.). Many such links are already included. Please let us know if you find errors or omissions, or have other suggestions.

On 32-bit platforms, any and all use of time in any way could be the source of Y2038 issues. On 64-bit systems, the platform usually provides a 64-bit time, which makes it possible to be Y2038 compliant. However, it is possible that variables with values of time in seconds get cast into 32-bit integers, perhaps when printing or conversion of some sort, or other processing. We therefore strongly advise that *ALL* usage of time be checked for Y2038 issues, even on 64-bit systems.

Please note that Y2038 issues are possible in “C” code outside of all standard uses. This is because times can come from external sources, such as embedded binary fields within network protocols and databases. Therefore, the approach of finding and fixing all of the functions listed below will not necessarily correct all Y2038 issues.