`json-c`

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

## JSON-C - A JSON implementation in C

Build Status

- AppVeyor Build
- Travis Build

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 with `git`, `gcc` and `autotools`

Home page for json-c: https://github.com/json-c/json-c/wiki

### Prerequisites:

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: 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

## 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 version 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)

## 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 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.

## 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:

JSON_C_DIR=/path/to/json_c/install
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