jsoncpp/README.md

JsonCpp

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

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.

Documentation

JsonCpp documentation is generated using Doxygen.

A note on backward-compatibility

• 1.y.z is built with C++11.
• 0.y.z can be used with older compilers.
• Major versions maintain binary-compatibility.

Using JsonCpp in your project

The recommended approach to integrating JsonCpp in your project is to include the amalgamated source (a single .cpp file and two .h files) in your project, and compile and build as you would any other source file. This ensures consistency of compilation flags and ABI compatibility, issues which arise when building shared or static libraries. See the next section 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 built as a dynamic library on Windows, then your project needs to define the macro JSON_DLL.

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.

Contributing to JsonCpp

Building and testing with Meson/Ninja

Thanks to David Seifert (@SoapGentoo), we (the maintainers) now use meson and ninja to build for debugging, as well as for continuous integration (see travis.sh ). Other systems may work, but minor things like version strings might break.

First, install both meson (which requires Python3) and ninja.

Then,

cd jsoncpp/
BUILD_TYPE=shared
#BUILD_TYPE=static
LIB_TYPE=debug
#LIB_TYPE=release
meson --buildtype ${BUILD_TYPE} --default-library ${LIB_TYPE} . build-${LIB_TYPE}
ninja -v -C build-${LIB_TYPE} test

Building and testing with other build systems

See https://github.com/open-source-parsers/jsoncpp/wiki/Building

Running the tests manually

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.

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.