C date and time functions

The C date and time functions are a group of functions in the standard library of the C programming language implementing date and time manipulation operations. They provide support for time acquisition, conversion between date formats, and formatted output to strings.

History
The format string used in  traces back to at least PWB/UNIX 1.0, released in 1977. Its  system command includes various formatting options. In 1989, the ANSI C standard is released including  and other date and time functions.

Overview of functions
The C date and time operations are defined in the  header file (  header in C++).

The timespec and related types were originally proposed by Markus Kuhn to provide a variety of time bases, but only TIME_UTC was accepted. The functionalities were, however, added to C++ in 2020 in std::chrono.

Example
The following C source code prints the current time to the standard output stream.

The output is: