Cron expression parsing in ANSI C

Given a cron expression and a date, you can get the next date which satisfies the cron expression.

Supports cron expressions with seconds field. Based on implementation of CronSequenceGenerator from Spring Framework.

Compiles and should work on Linux (GCC/Clang), Mac OS (Clang), Windows (MSVC), Android NDK, iOS and possibly on other platforms with time.h support.

Supports compilation in C (89) and in C++ modes.

Usage example

#include "ccronexpr.h"

cron_expr expr;
const char* err = NULL;
memset(&expr, 0, sizeof(expr));
cron_parse_expr("0 */2 1-4 * * *", &expr, &err);
if (err) ... /* invalid expression */
time_t cur = time(NULL);
time_t next = cron_next(&expr, cur);

Compilation and tests run examples

gcc ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c89 -DCRON_TEST_MALLOC -o a.out && ./a.out
g++ ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c++11 -DCRON_TEST_MALLOC -o a.out && ./a.out
g++ ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c++11 -DCRON_TEST_MALLOC -DCRON_COMPILE_AS_CXX -o a.out && ./a.out

clang ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c89 -DCRON_TEST_MALLOC -o a.out && ./a.out
clang++ ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c++11 -DCRON_TEST_MALLOC -o a.out && ./a.out
clang++ ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c++11 -DCRON_TEST_MALLOC -DCRON_COMPILE_AS_CXX -o a.out && ./a.out

cl ccronexpr.c ccronexpr_test.c /W4 /D_CRT_SECURE_NO_WARNINGS && ccronexpr.exe

Examples of supported expressions

Expression, input date, next date:

"*/15 * 1-4 * * *",  "2012-07-01_09:53:50", "2012-07-02_01:00:00"
"0 */2 1-4 * * *",   "2012-07-01_09:00:00", "2012-07-02_01:00:00"
"0 0 7 ? * MON-FRI", "2009-09-26_00:42:55", "2009-09-28_07:00:00"
"0 30 23 30 1/3 ?",  "2011-04-30_23:30:00", "2011-07-30_23:30:00"

See more examples in tests.

Timezones

This implementation does not support explicit timezones handling. By default, all dates are processed as UTC (GMT) dates without timezone information.

To use local dates (current system timezone) instead of GMT compile with -DCRON_USE_LOCAL_TIME, example:

gcc -DCRON_USE_LOCAL_TIME ccronexpr.c ccronexpr_test.c -I. -Wall -Wextra -std=c89 -DCRON_TEST_MALLOC -o a.out && TZ="America/Toronto" ./a.out

License information

This project is released under the Apache License 2.0.

Changelog

HEAD

• added CMake build
• added GitHub Workflow for continuous testing
• fixed type casts to support -Wconvert
• added tests for cron_prev and leap years
• fixed tests to work with CRON_USE_LOCAL_TIME
• added ESP-IDF usage guide

2019-03-27

• CRON_USE_LOCAL_TIME usage fixes

2018-05-23

• merged #8
• merged #9
• minor cleanups

2018-01-27

• merged #6
• updated license file (to the one parse-able by github)

2017-09-24

• merged #4

2016-06-17

• use thread-safe versions of gmtime and localtime

2015-02-28

• initial public version