Release date: 2019-07-28

SHA-256: a503214947952b69f0062f572cb74c17582a495767446347ce2e452963fc2ca4 (json.hpp), 541c34438fd54182e9cdc68dd20c898d766713ad6d901fb2c6e28ff1f1e7c10d (include.zip)

This release introduces a few convenience functions and performs a lot of house keeping (bug fixes and small improvements). All changes are backward-compatible.

- Add overload of the **[`contains`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_ab23b04802eb9da97dc3f664e54e09cb3.html#ab23b04802eb9da97dc3f664e54e09cb3) function** to check if a JSON pointer is valid without throwing exceptions, just like its [counterpart for object keys](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_a9286acdc0578fc66e9346323e69fc0e3.html#a9286acdc0578fc66e9346323e69fc0e3). #1600
- Add a function **[`to_string`](http://nlohmann.github.io/json/namespacenlohmann_a6ce645a0b8717757e096a5b5773b7a16.html#a6ce645a0b8717757e096a5b5773b7a16)** to allow for generic conversion to strings. #916 #1585
- Add **return value for the [`emplace_back`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_abf29131f898b05aad2c01a9c80e7a002.html#abf29131f898b05aad2c01a9c80e7a002) function**, returning a reference to the added element just like C++17 is [introducing this](https://en.cppreference.com/w/cpp/container/vector/emplace_back) for `std::vector`. #1609
- Add info how to use the library with the **[pacman](https://wiki.archlinux.org/index.php/pacman) package manager** on MSYS2. #1670

- Fix an issue where typedefs with certain names yielded a compilation error. #1642 #1643
- Fix a conversion to `std::string_view` in the unit tests. #1634 #1639
- Fix MSVC Debug build. #1536 #1570 #1608
- Fix [`get_to`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a65753c68f06639eda0d355f919564e01.html#a65753c68f06639eda0d355f919564e01) method to clear existing content before writing. #1511 #1555
- Fix a `-Wc++17-extensions` warning. `nodiscard` attributes are now only used with Clang when `-std=c++17` is used. #1535 #1551

- Switch from [Catch](https://github.com/philsquared/Catch) to **[doctest](https://github.com/onqtam/doctest)** for the unit tests which speeds up compilation and runtime of the 112,112,308 tests.
- Add an explicit section to the [README](https://github.com/nlohmann/json/blob/develop/README.md) about the **frequently addressed topics** [character encoding](https://github.com/nlohmann/json#character-encoding), [comments in JSON](https://github.com/nlohmann/json#comments-in-json), and the [order of object keys](https://github.com/nlohmann/json#order-of-object-keys).

- Use [`GNUInstallDirs`](https://cmake.org/cmake/help/v3.0/module/GNUInstallDirs.html) to set library install directories. #1673
- Fix links in the [README](https://github.com/nlohmann/json/blob/develop/README.md). #1620 #1621 #1622 #1623 #1625
- Mention [`json` type](http://nlohmann.github.io/json/namespacenlohmann_a2bfd99e845a2e5cd90aeaf1b1431f474.html#a2bfd99e845a2e5cd90aeaf1b1431f474) on the [documentation start page](http://nlohmann.github.io/json/index.html). #1616
- Complete documentation of [`value()` function](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_adcf8ca5079f5db993820bf50036bf45d.html#adcf8ca5079f5db993820bf50036bf45d) with respect to `type_error.302` exception. #1601
- Fix links in the documentation. #1598
- Add regression tests for MSVC. #1543 #1570
- Use **[CircleCI](http://circleci.com)** for [continuous integration](https://circleci.com/gh/nlohmann/json).
- Use **[Doozer](https://doozer.io)** for [continuous integration](https://doozer.io/nlohmann/json) on Linux (CentOS, Raspbian, Fedora)
- Add tests to check each CMake flag (`JSON_BuildTests`, `JSON_Install`, `JSON_MultipleHeaders`, `JSON_Sanitizer`, `JSON_Valgrind`, `JSON_NoExceptions`, `JSON_Coverage`).
- Use [Hedley](https://nemequ.github.io/hedley/) to avoid re-inventing several compiler-agnostic feature macros like `JSON_DEPRECATED`, `JSON_NODISCARD`, `JSON_LIKELY`, `JSON_UNLIKELY`, `JSON_HAS_CPP_14`, or `JSON_HAS_CPP_17`. Functions taking or returning pointers are annotated accordingly when a pointer will not be null.
- Build and run tests on [AppVeyor](https://ci.appveyor.com/project/nlohmann/json) in DEBUG and RELEASE mode.

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

- Function [`iterator_wrapper`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_af1592a06bc63811886ade4f9d965045e.html#af1592a06bc63811886ade4f9d965045e) are deprecated. Please use the member function [`items()`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_afe3e137ace692efa08590d8df40f58dd.html#afe3e137ace692efa08590d8df40f58dd) instead.
- Functions [`friend std::istream& operator<<(basic_json&, std::istream&)`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_ab7285a92514fcdbe6de505ebaba92ea3.html#ab7285a92514fcdbe6de505ebaba92ea3) and [`friend std::ostream& operator>>(const basic_json&, std::ostream&)`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_a9e06deabe69262c3ffc5533d32856983.html#a9e06deabe69262c3ffc5533d32856983) are deprecated. Please use [`friend std::istream&  operator>>(std::istream&, basic_json&)`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_aaf363408931d76472ded14017e59c9e8.html#aaf363408931d76472ded14017e59c9e8) and [`friend operator<<(std::ostream&, const basic_json&)`](http://nlohmann.github.io/json/classnlohmann_1_1basic__json_a5e34c5435e557d0bf666bd7311211405.html#a5e34c5435e557d0bf666bd7311211405) instead.