CronSim4Delphi

Cron Sim(ulator), a cron expression parser for Delphi 10+

This is a porting from CronSim for Python that you can find Here

Supported Cron Expression

CronSim supports Debian's cron implementation. You can find additional information in the original CronSim Readme

To explain some cron expressions compatible with CronSim you can refer to this on-line evaluator

Installation

Include CronSim.pas location in your Delphi's library path. The collection of helpers SCL.Types is required; you can find it Here

Usage

Simply create a new instance with TCronSim class:

var cron := TCronSim.New('*/5 * * * *').StartAt(EncodeDateTime(2025,1,1, 9,0,0,0));

The New method creates a new instance and returns its interface, which does not need to be explicitly destroyed.

The StartAt method sets the starting day and time for evaluating the cron expression.

At this point, using the Next method, you can iterate over all occurrences where the condition of the cron expression is met.

for var pass := 1 to 5 do
  writeln(cron.Next.ToStringFormat('dd/mm/yyyy  hh:nn:ss'));

Using for example the expression above, the output will be:

01/01/2025  09:05:00
01/01/2025  09:10:00
01/01/2025  09:15:00
01/01/2025  09:20:00
01/01/2025  09:25:00

alternatively you can iterate in reverse order:

cron.Reversed;

the loop above produces:

01/01/2025  08:55:00
01/01/2025  08:50:00
01/01/2025  08:45:00
01/01/2025  08:40:00
01/01/2025  08:35:00

The sample program test_cron allows you to test different cron expressions.

The maximum period that can be processed is 50 years.