Cron expression parsing in ANSI C
=================================

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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](https://github.com/spring-projects/spring-framework/blob/babbf6e8710ab937cd05ece20270f51490299270/spring-context/src/main/java/org/springframework/scheduling/support/CronSequenceGenerator.java) 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](https://github.com/staticlibs/ccronexpr/blob/a1343bc5a546b13430bd4ac72f3b047ac08f8192/ccronexpr_test.c#L251).

Timezones
---------

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

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](http://www.apache.org/licenses/LICENSE-2.0).

Changelog
---------

**2019-03-27**

 * `CRON_USE_LOCAL_TIME` usage fixes

**2018-05-23**

 * merged [#8](https://github.com/staticlibs/ccronexpr/pull/8)
 * merged [#9](https://github.com/staticlibs/ccronexpr/pull/9)
 * minor cleanups

**2018-01-27**

 * merged [#6](https://github.com/staticlibs/ccronexpr/pull/6)
 * updated license file (to the one parse-able by github)

**2017-09-24**

 * merged [#4](https://github.com/staticlibs/ccronexpr/pull/4)

**2016-06-17**

 * use thread-safe versions of `gmtime` and `localtime`

**2015-02-28**

 * initial public version