- Overview and Build Status
- Building on Unix
- Install Prerequisites
- Building with partial threading support
- Building with CMake
- Linking to libjson-c
- Using json-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.
Home page for json-c: https://github.com/json-c/json-c/wiki
See also the "Installing prerequisites" section below.
gcc
,clang
, or another C compilerlibtool>=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
json-c
GitHub repo: https://github.com/json-c/json-c
$ git clone https://github.com/json-c/json-c.git
$ cd json-c
$ sh autogen.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
If you are on a relatively modern system, you'll likely be able to install the prerequisites using your OS's packaging system.
sudo apt install git
sudo apt install autoconf automake libtool
sudo apt install valgrind # optional
Then start from the "git clone" command, above.
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 http://ftp.gnu.org/gnu/autoconf/autoconf-2.69.tar.gz
curl -O http://ftp.gnu.org/gnu/automake/automake-1.15.tar.gz
curl -O http://ftp.gnu.org/gnu/libtool/libtool-2.2.6b.tar.gz
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)
Although json-c does not support fully multi-threaded access to object trees, it has some code to help make 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 https://stackoverflow.com/a/11609063, 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 randomly 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.
To use CMake, build it like:
mkdir build
cd build
cmake ../
make
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.
cmake -DBUILD_SHARED_LIBS=OFF ...
If your system has pkgconfig
,
then you can just add this to your makefile
:
CFLAGS += $(shell pkg-config --cflags json-c)
LDFLAGS += $(shell pkg-config --libs json-c)
Without pkgconfig
, you would do something like this:
JSON_C_DIR=/path/to/json_c/install
CFLAGS += -I$(JSON_C_DIR)/include/json-c
LDFLAGS+= -L$(JSON_C_DIR)/lib -ljson-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