# Date

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**[Try it out on wandbox!](https://wandbox.org/permlink/L8MwjzSSC3fXXrMd)**

## Summary

This is actually several separate C++11/C++14/C++17 libraries:

1. `"date.h"` is a header-only library which builds upon `<chrono>`.  It adds some new `duration` types, and new `time_point` types.  It also adds "field" types such as `year_month_day` which is a struct `{year, month, day}`.  And it provides convenient means to convert between the "field" types and the `time_point` types.

    * Documentation: http://howardhinnant.github.io/date/date.html
    * Video: https://www.youtube.com/watch?v=tzyGjOm8AKo
    * Slides: http://schd.ws/hosted_files/cppcon2015/43/hinnant_dates.pdf

1. `"tz.h"` / `"tz.cpp"`  are a timezone library built on top of the `"date.h"` library.  This timezone library is a complete parser of the IANA timezone database.  It provides for an easy way to access all of the data in this database, using the types from `"date.h"` and `<chrono>`.  The IANA database also includes data on leap seconds, and this library provides utilities to compute with that information as well.

    * Documentation: http://howardhinnant.github.io/date/tz.html
    * Video: https://www.youtube.com/watch?v=Vwd3pduVGKY
    * Slides: http://schd.ws/hosted_files/cppcon2016/0f/Welcome%20To%20The%20Time%20Zone%20-%20Howard%20Hinnant%20-%20CppCon%202016.pdf

1. `"iso_week.h"` is a header-only library built on top of the `"date.h"` library which implements the ISO week date calendar.

    * Documentation: http://howardhinnant.github.io/date/iso_week.html

1. `"julian.h"` is a header-only library built on top of the `"date.h"` library which implements a proleptic Julian calendar which is fully interoperable with everything above.

    * Documentation: http://howardhinnant.github.io/date/julian.html

1. `"islamic.h"` is a header-only library built on top of the `"date.h"` library which implements a proleptic Islamic calendar which is fully interoperable with everything above.

    * Documentation: http://howardhinnant.github.io/date/islamic.html

## Standardization

Slightly modified versions of `"date.h"` and `"tz.h"` were voted into the C++20 working draft at the Jacksonville FL meeting on 2018-03-17:

* http://howardhinnant.github.io/date/d0355r7.html

## Build & Test

You can download and install Date using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:

    git clone https://github.com/Microsoft/vcpkg.git
    cd vcpkg
    ./bootstrap-vcpkg.sh
    ./vcpkg integrate install
    vcpkg install date

The Date port in vcpkg is updated by Microsoft team members and community contributors. If the version falls behind, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.

You can optionally build using [CMake](https://cmake.org/). Here is a guide of how to build and test using the CMake Makefile generator.

```bash
mkdir build
cd build
cmake ../
cmake --build . --target testit # Consider '-- -j4' for multithreading
```
## Projects using this library

* www.safe.com
* www.webtoolkit.eu/wt
* https://github.com/ViewTouch/viewtouch
* https://routinghub.com
* https://github.com/valhalla

If you would like your project (or product) on this list, just let me know.