xref: /external/jsoncpp

Introduction
------------

[JSON][json-org] is a lightweight data-interchange format. It can represent
numbers, strings, ordered sequences of values, and collections of name/value
pairs.

[json-org]: http://json.org/

JsonCpp is a C++ library that allows manipulating JSON values, including
serialization and deserialization to and from strings. It can also preserve
existing comment in unserialization/serialization steps, making it a convenient
format to store user input files.

## A note on backward-compatibility
Very soon, we are switching to C++11 only. For older compilers, try the `pre-C++11` branch.

Using JsonCpp in your project
-----------------------------

The recommended approach to integrating JsonCpp in your project is to build
the amalgamated source (a single `.cpp` file) with your own build system. This
ensures consistency of compilation flags and ABI compatibility. See the section
"Generating amalgamated source and header" for instructions.
  
The `include/` should be added to your compiler include path. Jsoncpp headers
should be included as follow:

    #include <json/json.h>

If JsonCpp was build as a dynamic library on Windows, then your project needs to
define the macro `JSON_DLL`.


Building and testing with new CMake
-----------------------------------

[CMake][] is a C++ Makefiles/Solution generator. It is usually available on most
Linux system as package. On Ubuntu:

    sudo apt-get install cmake

[CMake]: http://www.cmake.org

Note that Python is also required to run the JSON reader/writer tests. If
missing, the build will skip running those tests.

When running CMake, a few parameters are required:

* a build directory where the makefiles/solution are generated. It is also used
  to store objects, libraries and executables files.
* the generator to use: makefiles or Visual Studio solution? What version or
  Visual Studio, 32 or 64 bits solution? 

Steps for generating solution/makefiles using `cmake-gui`:

* Make "source code" point to the source directory.
* Make "where to build the binary" point to the directory to use for the build.
* Click on the "Grouped" check box.
* Review JsonCpp build options (tick `JSONCPP_LIB_BUILD_SHARED` to build as a
  dynamic library).
* Click the configure button at the bottom, then the generate button.
* The generated solution/makefiles can be found in the binary directory.

Alternatively, from the command-line on Unix in the source directory:

    mkdir -p build/debug
    cd build/debug
    cmake -DCMAKE_BUILD_TYPE=debug -DJSONCPP_LIB_BUILD_SHARED=OFF -G "Unix Makefiles" ../..
    make

Running `cmake -`" will display the list of available generators (passed using
the `-G` option).

By default CMake hides compilation commands. This can be modified by specifying
`-DCMAKE_VERBOSE_MAKEFILE=true` when generating makefiles.


Building and testing with SCons
-------------------------------

**Note:** The SCons-based build system is deprecated. Please use CMake; see the
section above.

JsonCpp can use [Scons][] as a build system. Note that SCons requires Python to
be installed.

[SCons]: http://www.scons.org/

Invoke SCons as follows:

    scons platform=$PLATFORM [TARGET]

where `$PLATFORM` may be one of:

* `suncc`: Sun C++ (Solaris)
* `vacpp`: Visual Age C++ (AIX)
* `mingw`
* `msvc6`: Microsoft Visual Studio 6 service pack 5-6
* `msvc70`: Microsoft Visual Studio 2002
* `msvc71`: Microsoft Visual Studio 2003
* `msvc80`: Microsoft Visual Studio 2005
* `msvc90`: Microsoft Visual Studio 2008
* `linux-gcc`: Gnu C++ (linux, also reported to work for Mac OS X)

If you are building with Microsoft Visual Studio 2008, you need to set up the
environment by running `vcvars32.bat` (e.g. MSVC 2008 command prompt) before
running SCons.


Running the tests manually
--------------------------

Note that test can be run using SCons using the `check` target:

    scons platform=$PLATFORM check

You need to run tests manually only if you are troubleshooting an issue.

In the instructions below, replace `path/to/jsontest` with the path of the
`jsontest` executable that was compiled on your platform.

    cd test
    # This will run the Reader/Writer tests
    python runjsontests.py path/to/jsontest
    
    # This will run the Reader/Writer tests, using JSONChecker test suite
    # (http://www.json.org/JSON_checker/).
    # Notes: not all tests pass: JsonCpp is too lenient (for example,
    # it allows an integer to start with '0'). The goal is to improve
    # strict mode parsing to get all tests to pass.
    python runjsontests.py --with-json-checker path/to/jsontest
    
    # This will run the unit tests (mostly Value)
    python rununittests.py path/to/test_lib_json
    
    # You can run the tests using valgrind:
    python rununittests.py --valgrind path/to/test_lib_json


Building the documentation
--------------------------

Run the Python script `doxybuild.py` from the top directory:

    python doxybuild.py --doxygen=$(which doxygen) --open --with-dot

See `doxybuild.py --help` for options.


Generating amalgamated source and header
----------------------------------------

JsonCpp is provided with a script to generate a single header and a single
source file to ease inclusion into an existing project. The amalgamated source
can be generated at any time by running the following command from the
top-directory (this requires Python 2.6):

    python amalgamate.py

It is possible to specify header name. See the `-h` option for detail.

By default, the following files are generated:
* `dist/jsoncpp.cpp`: source file that needs to be added to your project.
* `dist/json/json.h`: corresponding header file for use in your project. It is
  equivalent to including `json/json.h` in non-amalgamated source. This header
  only depends on standard headers.
* `dist/json/json-forwards.h`: header that provides forward declaration of all
  JsonCpp types.

The amalgamated sources are generated by concatenating JsonCpp source in the
correct order and defining the macro `JSON_IS_AMALGAMATION` to prevent inclusion
of other headers.


Adding a reader/writer test
---------------------------

To add a test, you need to create two files in test/data:

* a `TESTNAME.json` file, that contains the input document in JSON format.
* a `TESTNAME.expected` file, that contains a flatened representation of the
  input document.

The `TESTNAME.expected` file format is as follows:

* each line represents a JSON element of the element tree represented by the
  input document.
* each line has two parts: the path to access the element separated from the
  element value by `=`. Array and object values are always empty (i.e.
  represented by either `[]` or `{}`).
* element path: `.` represents the root element, and is used to separate object
  members. `[N]` is used to specify the value of an array element at index `N`.

See the examples `test_complex_01.json` and `test_complex_01.expected` to better
understand element paths.


Understanding reader/writer test output
---------------------------------------

When a test is run, output files are generated beside the input test files.
Below is a short description of the content of each file:

* `test_complex_01.json`: input JSON document.
* `test_complex_01.expected`: flattened JSON element tree used to check if
  parsing was corrected.
* `test_complex_01.actual`: flattened JSON element tree produced by `jsontest`
  from reading `test_complex_01.json`.
* `test_complex_01.rewrite`: JSON document written by `jsontest` using the
  `Json::Value` parsed from `test_complex_01.json` and serialized using
  `Json::StyledWritter`.
* `test_complex_01.actual-rewrite`: flattened JSON element tree produced by
  `jsontest` from reading `test_complex_01.rewrite`.
* `test_complex_01.process-output`: `jsontest` output, typically useful for
  understanding parsing errors.


License
-------

See the `LICENSE` file for details. In summary, JsonCpp is licensed under the
MIT license, or public domain if desired and recognized in your jurisdiction.