Strftime

strftime is a function used to format date and time according to a format specification. It is most commonly associated with the C standard library, where strftime is declared in time.h and converts a broken-down time represented by a struct tm into a character string according to a format string. The function requires a destination buffer, its size, the format string, and a pointer to the time data. It returns the number of characters placed in the buffer, not including the terminating null character, or zero if the output does not fit or an error occurs.

Format specifiers in strftime begin with a percent sign and indicate which components of the time should appear in the output. The exact set of codes is defined by the C standard and can vary by implementation and locale. Common codes include %Y for the year with century, %m for the month, %d for the day of month, %H for the hour (24-hour clock), %M for minutes, %S for seconds, and %p for AM or PM. Some implementations provide additional shortcuts such as %F (ISO 8601 date) or %T (HH:MM:SS). Locale settings influence the textual names of months and days, as well as the language of AM/PM markers.

Beyond C, many languages offer strftime-like functionality with similar syntax. Python, for example, provides time.strftime which returns a string; other languages such as Ruby and PHP include their own locale-aware variants. While the core idea is consistent, specific codes and behavior can differ across libraries and locales.