Date

Definition

Lightweight date and time utilities used by the fpx preprocessor.

This module provides a compact datetime type together with a small set of date/time operations required by fpx. Its primary purpose is to support expansion of the predefined macros:

• __DATE__
• __TIME__
• __TIMESTAMP__

Rather than providing a complete calendaring framework, this module focuses on the functionality required by preprocessing tasks:

• Retrieval of the current local date and time using date_and_time()
• Construction of datetime objects from numeric components or strings
• Parsing of commonly encountered date/time representations
• Flexible formatting through to_string(fmt)
• Day-of-week computation using Zeller's congruence

The implementation deliberately remains lightweight and dependency-free. It is not intended to replace dedicated date/time libraries, but instead provides exactly the capabilities required by fpx while remaining portable across standard-conforming Fortran compilers.

Examples

1. Expanding predefined macros:

      type(datetime) :: dt
    
      dt = now()
    
      print *, '__DATE__      -> ', dt%to_string('MMM-dd-yyyy')
      print *, '__TIME__      -> ', dt%to_string('HH:mm:ss')
      print *, '__TIMESTAMP__ -> ', dt%to_string('ddd-MMM-yyyy HH:mm:ss')

2. Constructing a datetime from a string:

      type(datetime) :: build_time
    
      build_time = datetime('2025-08-12 09:30:00')
    
      print *, build_time%to_string('ddd-MMM-yyyy')

3. Constructing a datetime from components:

      type(datetime) :: epoch
    
      epoch = datetime(1970, 1, 1)
    
      print *, epoch%to_string()

4. Timestamping preprocessing operations:

      type(datetime) :: dt
    
      dt = now()
      print *, 'Preprocessing started at ', dt%to_string('HH:mm:ss')

Data Types
interface	datetime
	Compact representation of date and time Stores all components in minimal integer kinds to reduce memory usage. All fields are public for easy access. More...