1 \mainpage 2 3 `json-c` 4 ======== 5 6 1. [Overview and Build Status](#overview) 7 2. [Building on Unix](#buildunix) 8 * [Prerequisites](#installprereq) 9 * [Build commands](#buildcmds) 10 3. [CMake options](#CMake) 11 4. [Testing](#testing) 12 5. [Building with `vcpkg`](#buildvcpkg) 13 6. [Linking to libjson-c](#linking) 14 7. [Using json-c](#using) 15 16 JSON-C - A JSON implementation in C <a name="overview"></a> 17 ----------------------------------- 18 19 Build Status 20 * [AppVeyor Build](https://ci.appveyor.com/project/hawicz/json-c)  21 * [Travis Build](https://travis-ci.org/json-c/json-c)  22 23 Test Status 24 * [Coveralls](https://coveralls.io/github/json-c/json-c?branch=master) [](https://coveralls.io/github/json-c/json-c?branch=master) 25 26 JSON-C implements a reference counting object model that allows you to easily 27 construct JSON objects in C, output them as JSON formatted strings and parse 28 JSON formatted strings back into the C representation of JSON objects. 29 It aims to conform to [RFC 7159](https://tools.ietf.org/html/rfc7159). 30 31 Building on Unix with `git`, `gcc` and `cmake` <a name="buildunix"></a> 32 -------------------------------------------------- 33 34 Home page for json-c: https://github.com/json-c/json-c/wiki 35 36 ### Prerequisites: <a name="installprereq"></a> 37 38 - `gcc`, `clang`, or another C compiler 39 40 - cmake>=2.8, >=3.16 recommended 41 42 To generate docs you'll also need: 43 - `doxygen>=1.8.13` 44 45 If you are on a relatively modern system, you'll likely be able to install 46 the prerequisites using your OS's packaging system. 47 48 ### Install using apt (e.g. Ubuntu 16.04.2 LTS) 49 ```sh 50 sudo apt install git 51 sudo apt install cmake 52 sudo apt install doxygen # optional 53 sudo apt install valgrind # optional 54 ``` 55 56 ### Build instructions: <a name="buildcmds"></a> 57 58 `json-c` GitHub repo: https://github.com/json-c/json-c 59 60 ```sh 61 $ git clone https://github.com/json-c/json-c.git 62 $ mkdir json-c-build 63 $ cd json-c-build 64 $ cmake ../json-c # See CMake section below for custom arguments 65 ``` 66 67 Note: it's also possible to put your build directory inside the json-c 68 source directory, or even not use a separate build directory at all, but 69 certain things might not work quite right (notably, `make distcheck`) 70 71 Then: 72 73 ```sh 74 $ make 75 $ make test 76 $ make USE_VALGRIND=0 test # optionally skip using valgrind 77 $ make install 78 ``` 79 80 81 ### Generating documentation with Doxygen: 82 83 The libray documentation can be generated directly from the source codes using Doxygen tool: 84 85 ```sh 86 # in build directory 87 make doc 88 google-chrome doc/html/index.html 89 ``` 90 91 92 CMake Options <a name="CMake"></a> 93 -------------------- 94 95 The json-c library is built with [CMake](https://cmake.org/cmake-tutorial/), 96 which can take a few options. 97 98 Variable | Type | Description 99 -----------------------------|--------|-------------- 100 CMAKE_INSTALL_PREFIX | String | The install location. 101 CMAKE_BUILD_TYPE | String | Defaults to "debug". 102 BUILD_SHARED_LIBS | Bool | The default build generates a dynamic (dll/so) library. Set this to OFF to create a static library only. 103 BUILD_STATIC_LIBS | Bool | The default build generates a static (lib/a) library. Set this to OFF to create a shared library only. 104 DISABLE_STATIC_FPIC | Bool | The default builds position independent code. Set this to OFF to create a shared library only. 105 DISABLE_BSYMBOLIC | Bool | Disable use of -Bsymbolic-functions. 106 DISABLE_THREAD_LOCAL_STORAGE | Bool | Disable use of Thread-Local Storage (HAVE___THREAD). 107 DISABLE_WERROR | Bool | Disable use of -Werror. 108 ENABLE_RDRAND | Bool | Enable RDRAND Hardware RNG Hash Seed. 109 ENABLE_THREADING | Bool | Enable partial threading support. 110 OVERRIDE_GET_RANDOM_SEED | String | A block of code to use instead of the default implementation of json_c_get_random_seed(), e.g. on embedded platforms where not even the fallback to time() works. Must be a single line. 111 112 Pass these options as `-D` on CMake's command-line. 113 114 ```sh 115 # build a static library only 116 cmake -DBUILD_SHARED_LIBS=OFF .. 117 ``` 118 119 ### Building with partial threading support 120 121 Although json-c does not support fully multi-threaded access to 122 object trees, it has some code to help make its use in threaded programs 123 a bit safer. Currently, this is limited to using atomic operations for 124 json_object_get() and json_object_put(). 125 126 Since this may have a performance impact, of at least 3x slower 127 according to https://stackoverflow.com/a/11609063, it is disabled by 128 default. You may turn it on by adjusting your cmake command with: 129 -DENABLE_THREADING=ON 130 131 Separately, the default hash function used for object field keys, 132 lh_char_hash, uses a compare-and-swap operation to ensure the random 133 seed is only generated once. Because this is a one-time operation, it 134 is always compiled in when the compare-and-swap operation is available. 135 136 137 ### cmake-configure wrapper script 138 139 For those familiar with the old autoconf/autogen.sh/configure method, 140 there is a `cmake-configure` wrapper script to ease the transition to cmake. 141 142 ```sh 143 mkdir build 144 cd build 145 ../cmake-configure --prefix=/some/install/path 146 make 147 ``` 148 149 cmake-configure can take a few options. 150 151 | options | Description| 152 | ---- | ---- | 153 | prefix=PREFIX | install architecture-independent files in PREFIX | 154 | enable-threading | Enable code to support partly multi-threaded use | 155 | enable-rdrand | Enable RDRAND Hardware RNG Hash Seed generation on supported x86/x64 platforms. | 156 | enable-shared | build shared libraries [default=yes] | 157 | enable-static | build static libraries [default=yes] | 158 | disable-Bsymbolic | Avoid linking with -Bsymbolic-function | 159 | disable-werror | Avoid treating compiler warnings as fatal errors | 160 161 162 Testing: <a name="testing"></a> 163 ---------- 164 165 By default, if valgrind is available running tests uses it. 166 That can slow the tests down considerably, so to disable it use: 167 ```sh 168 export USE_VALGRIND=0 169 ``` 170 171 To run tests a separate build directory is recommended: 172 ```sh 173 mkdir build-test 174 cd build-test 175 # VALGRIND=1 causes -DVALGRIND=1 to be passed when compiling code 176 # which uses slightly slower, but valgrind-safe code. 177 VALGRIND=1 cmake .. 178 make 179 180 make test 181 # By default, if valgrind is available running tests uses it. 182 make USE_VALGRIND=0 test # optionally skip using valgrind 183 ``` 184 185 If a test fails, check `Testing/Temporary/LastTest.log`, 186 `tests/testSubDir/${testname}/${testname}.vg.out`, and other similar files. 187 If there is insufficient output try: 188 ```sh 189 VERBOSE=1 make test 190 ``` 191 or 192 ```sh 193 JSONC_TEST_TRACE=1 make test 194 ``` 195 and check the log files again. 196 197 198 Building on Unix and Windows with `vcpkg` <a name="buildvcpkg"></a> 199 -------------------------------------------------- 200 201 You can download and install JSON-C using the [vcpkg](https://github.com/Microsoft/vcpkg/) dependency manager: 202 203 git clone https://github.com/Microsoft/vcpkg.git 204 cd vcpkg 205 ./bootstrap-vcpkg.sh 206 ./vcpkg integrate install 207 vcpkg install json-c 208 209 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](https://github.com/Microsoft/vcpkg) on the vcpkg repository. 210 211 212 Linking to `libjson-c` <a name="linking"> 213 ---------------------- 214 215 If your system has `pkgconfig`, 216 then you can just add this to your `makefile`: 217 218 ```make 219 CFLAGS += $(shell pkg-config --cflags json-c) 220 LDFLAGS += $(shell pkg-config --libs json-c) 221 ``` 222 223 Without `pkgconfig`, you would do something like this: 224 225 ```make 226 JSON_C_DIR=/path/to/json_c/install 227 CFLAGS += -I$(JSON_C_DIR)/include/json-c 228 LDFLAGS+= -L$(JSON_C_DIR)/lib -ljson-c 229 ``` 230 231 232 Using json-c <a name="using"> 233 ------------ 234 235 To use json-c you can either include json.h, or preferrably, one of the 236 following more specific header files: 237 238 * json_object.h - Core types and methods. 239 * json_tokener.h - Methods for parsing and serializing json-c object trees. 240 * json_pointer.h - JSON Pointer (RFC 6901) implementation for retrieving 241 objects from a json-c object tree. 242 * json_object_iterator.h - Methods for iterating over single json_object instances. (See also `json_object_object_foreach()` in json_object.h) 243 * json_visit.h - Methods for walking a tree of json-c objects. 244 * json_util.h - Miscelleanous utility functions. 245 246 For a full list of headers see [files.html](http://json-c.github.io/json-c/json-c-current-release/doc/html/files.html) 247 248 The primary type in json-c is json_object. It describes a reference counted 249 tree of json objects which are created by either parsing text with a 250 json_tokener (i.e. `json_tokener_parse_ex()`), or by creating 251 (with `json_object_new_object()`, `json_object_new_int()`, etc...) and adding 252 (with `json_object_object_add()`, `json_object_array_add()`, etc...) them 253 individually. 254 Typically, every object in the tree will have one reference, from it's parent. 255 When you are done with the tree of objects, you call json_object_put() on just 256 the root object to free it, which recurses down through any child objects 257 calling json_object_put() on each one of those in turn. 258 259 You can get a reference to a single child 260 (`json_object_object_get()` or `json_object_array_get_idx()`) 261 and use that object as long as its parent is valid. 262 If you need a child object to live longer than its parent, you can 263 increment the child's refcount (`json_object_get()`) to allow it to survive 264 the parent being freed or it being removed from its parent 265 (`json_object_object_del()` or `json_object_array_del_idx()`) 266 267 When parsing text, the json_tokener object is independent from the json_object 268 that it returns. It can be allocated (`json_tokener_new()`) 269 used ones or multiple times (`json_tokener_parse_ex()`, and 270 freed (`json_tokener_free()`) while the json_object objects live on. 271 272 A json_object tree can be serialized back into a string with 273 `json_object_to_json_string_ext()`. The string that is returned 274 is only valid until the next "to_json_string" call on that same object. 275 Also, it is freed when the json_object is freed. 276
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