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  1. Overview and Build Status
  2. Building on Unix
  3. Install Prerequisites
  4. Building with partial threading support
  5. Building with CMake
  6. Linking to libjson-c
  7. Using json-c

JSON-C - A JSON implementation in C

Build Status

JSON-C implements a reference counting object model that allows you to easily construct JSON objects in C, output them as JSON formatted strings and parse JSON formatted strings back into the C representation of JSON objects. It aims to conform to RFC 7159.

Building on Unix and Windows with vcpkg, gcc/g++, curl, unzip, and tar

You can download and install JSON-C using the vcpkg dependency manager:

git clone
cd vcpkg
./vcpkg integrate install
vcpkg install json-c

The JSON-C port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.

Building on Unix with git, gcc and autotools

Home page for json-c:


See also the "Installing prerequisites" section below.

  • gcc, clang, or another C compiler
  • libtool>=2.2.6b

If you're not using a release tarball, you'll also need:

  • autoconf>=2.64 (autoreconf)
  • automake>=1.13

Make sure you have a complete libtool install, including libtoolize.

To generate docs (e.g. as part of make distcheck) you'll also need:

  • doxygen>=1.8.13

Build instructions:

json-c GitHub repo:

$ git clone
$ cd json-c
$ sh

followed by

$ ./configure  # --enable-threading
$ make
$ make install

To build and run the test programs:

$ make check
$ make USE_VALGRIND=0 check   # optionally skip using valgrind

Install prerequisites

If you are on a relatively modern system, you'll likely be able to install the prerequisites using your OS's packaging system.

Install using apt (e.g. Ubuntu 16.04.2 LTS)

sudo apt install git
sudo apt install autoconf automake libtool
sudo apt install valgrind # optional

Then start from the "git clone" command, above.

Manually install and build autoconf, automake and libtool

For older OS's that don't have up-to-date versions of the packages will require a bit more work. For example, CentOS release 5.11, etc...

curl -O
curl -O
curl -O

tar xzf autoconf-2.69.tar.gz
tar xzf automake-1.15.tar.gz
tar xzf libtool-2.2.6b.tar.gz

export PATH=${HOME}/ac_install/bin:$PATH

(cd autoconf-2.69 && \
  ./configure --prefix ${HOME}/ac_install && \
  make && \
  make install)

(cd automake-1.15 && \
  ./configure --prefix ${HOME}/ac_install && \
  make && \
  make install)

(cd libtool-2.2.6b && \
  ./configure --prefix ${HOME}/ac_install && \
  make && \
  make install)

Building with partial threading support

Although json-c does not support fully multi-threaded access to object trees, it has some code to help make its use in threaded programs a bit safer. Currently, this is limited to using atomic operations for json_object_get() and json_object_put().

Since this may have a performance impact, of at least 3x slower according to, it is disabled by default. You may turn it on by adjusting your configure command with: --enable-threading

Separately, the default hash function used for object field keys, lh_char_hash, uses a compare-and-swap operation to ensure the random seed is only generated once. Because this is a one-time operation, it is always compiled in when the compare-and-swap operation is available.

Building with CMake

To use CMake, build it like:

mkdir build
cd build
cmake ../

CMake can take a few options.

Variable Type Description
CMAKE_INSTALL_PREFIX String The install location.
BUILD_SHARED_LIBS Bool The default build generates a dynamic (dll/so) library. Set this to OFF to create a static library instead.
ENABLE_RDRAND Bool Enable RDRAND Hardware RNG Hash Seed
ENABLE_THREADING Bool Enable partial threading support

Pass these options as -D on CMake's command-line.


Testing with cmake:

By default, if valgrind is available running tests uses it. That can slow the tests down considerably, so to disable it use:


To run tests:

mkdir build-test
cd build-test
# VALGRIND=1 causes -DVALGRIND=1 to be included when building
VALGRIND=1 cmake ..

make test
# By default, if valgrind is available running tests uses it.
make USE_VALGRIND=0 test   # optionally skip using valgrind

If a test fails, check Testing/Temporary/LastTest.log, tests/testSubDir/${testname}/${testname}.vg.out, and other similar files. If there is insufficient output try:

VERBOSE=1 make test


JSONC_TEST_TRACE=1 make test

and check the log files again.

Linking to libjson-c

If your system has pkgconfig, then you can just add this to your makefile:

CFLAGS += $(shell pkg-config --cflags json-c)
LDFLAGS += $(shell pkg-config --libs json-c)

Without pkgconfig, you would do something like this:

CFLAGS += -I$(JSON_C_DIR)/include/json-c
LDFLAGS+= -L$(JSON_C_DIR)/lib -ljson-c

Using json-c

To use json-c you can either include json.h, or preferrably, one of the following more specific header files:

  • json_object.h - Core types and methods.
  • json_tokener.h - Methods for parsing and serializing json-c object trees.
  • json_pointer.h - JSON Pointer (RFC 6901) implementation for retrieving objects from a json-c object tree.
  • json_object_iterator.h - Methods for iterating over single json_object instances.
  • json_visit.h - Methods for walking a tree of json-c objects.
  • json_util.h - Miscelleanous utility functions.

For a full list of headers see files.html

About is the official code repository for json-c. See the wiki for release tarballs for download. API docs at







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