1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 2 <html xmlns="http://www.w3.org/1999/xhtml"> 3 <head> 4 <meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/> 5 <meta http-equiv="X-UA-Compatible" content="IE=9"/> 6 <title>json-c: Main Page</title> 7 <link href="tabs.css" rel="stylesheet" type="text/css"/> 8 <script type="text/javascript" src="jquery.js"></script> 9 <script type="text/javascript" src="dynsections.js"></script> 10 <link href="doxygen.css" rel="stylesheet" type="text/css" /> 11 </head> 12 <body> 13 <div id="top"><!-- do not remove this div, it is closed by doxygen! --> 14 <div id="titlearea"> 15 <table cellspacing="0" cellpadding="0"> 16 <tbody> 17 <tr style="height: 56px;"> 18 <td style="padding-left: 0.5em;"> 19 <div id="projectname">json-c 20  <span id="projectnumber">0.15</span> 21 </div> 22 </td> 23 </tr> 24 </tbody> 25 </table> 26 </div> 27 <!-- end header part --> 28 <!-- Generated by Doxygen 1.8.2 --> 29 <div id="navrow1" class="tabs"> 30 <ul class="tablist"> 31 <li class="current"><a href="index.html"><span>Main Page</span></a></li> 32 <li><a href="pages.html"><span>Related Pages</span></a></li> 33 <li><a href="annotated.html"><span>Data Structures</span></a></li> 34 <li><a href="files.html"><span>Files</span></a></li> 35 </ul> 36 </div> 37 </div><!-- top --> 38 <div class="header"> 39 <div class="headertitle"> 40 <div class="title">json-c Documentation</div> </div> 41 </div><!--header--> 42 <div class="contents"> 43 <div class="textblock"><h1><code>json-c</code></h1> 44 <ol type="1"> 45 <li><a href="#overview">Overview and Build Status</a></li> 46 <li><a href="#buildunix">Building on Unix</a><ul> 47 <li><a href="#installprereq">Prerequisites</a></li> 48 <li><a href="#buildcmds">Build commands</a></li> 49 </ul> 50 </li> 51 <li><a href="#CMake">CMake options</a></li> 52 <li><a href="#testing">Testing</a></li> 53 <li><a href="#buildvcpkg">Building with `vcpkg`</a></li> 54 <li><a href="#linking">Linking to libjson-c</a></li> 55 <li><a href="#using">Using json-c</a></li> 56 </ol> 57 <h2>JSON-C - A JSON implementation in C <a class="anchor" id="overview"></a></h2> 58 <p>Build Status</p> 59 <ul> 60 <li><a href="https://ci.appveyor.com/project/hawicz/json-c">AppVeyor Build</a> <div class="image"> 61 <img src="https://ci.appveyor.com/api/projects/status/github/json-c/json-c?branch=master&svg=true" alt="AppVeyor Build Status"/> 62 </div> 63 </li> 64 <li><a href="https://travis-ci.org/json-c/json-c">Travis Build</a> <div class="image"> 65 <img src="https://travis-ci.org/json-c/json-c.svg?branch=master" alt="Travis Build Status"/> 66 </div> 67 </li> 68 </ul> 69 <p>Test Status</p> 70 <ul> 71 <li><a href="https://coveralls.io/github/json-c/json-c?branch=master">Coveralls</a> <a href="https://coveralls.io/github/json-c/json-c?branch=master"></a></li> 72 </ul> 73 <p>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 <a href="https://tools.ietf.org/html/rfc7159">RFC 7159</a>.</p> 74 <h2>Building on Unix with <code>git</code>, <code>gcc</code> and <code>cmake</code> <a class="anchor" id="buildunix"></a></h2> 75 <p>Home page for json-c: <a href="https://github.com/json-c/json-c/wiki">https://github.com/json-c/json-c/wiki</a></p> 76 <h3>Prerequisites: <a class="anchor" id="installprereq"></a></h3> 77 <ul> 78 <li><code>gcc</code>, <code>clang</code>, or another C compiler</li> 79 </ul> 80 <ul> 81 <li>cmake>=2.8, >=3.16 recommended</li> 82 </ul> 83 <p>To generate docs you'll also need:</p> 84 <ul> 85 <li><code>doxygen>=1.8.13</code></li> 86 </ul> 87 <p>If you are on a relatively modern system, you'll likely be able to install the prerequisites using your OS's packaging system.</p> 88 <h3>Install using apt (e.g. Ubuntu 16.04.2 LTS)</h3> 89 <pre class="fragment">sudo apt install git 90 sudo apt install cmake 91 sudo apt install doxygen # optional 92 sudo apt install valgrind # optional 93 </pre><h3>Build instructions: <a class="anchor" id="buildcmds"></a></h3> 94 <p><code>json-c</code> GitHub repo: <a href="https://github.com/json-c/json-c">https://github.com/json-c/json-c</a> </p> 95 <pre class="fragment">$ git clone https://github.com/json-c/json-c.git 96 $ mkdir json-c-build 97 $ cd json-c-build 98 $ cmake ../json-c # See CMake section below for custom arguments 99 </pre><p>Note: it's also possible to put your build directory inside the json-c source directory, or even not use a separate build directory at all, but certain things might not work quite right (notably, <code>make distcheck</code>)</p> 100 <p>Then: </p> 101 <pre class="fragment">$ make 102 $ make test 103 $ make USE_VALGRIND=0 test # optionally skip using valgrind 104 $ make install 105 </pre><h3>Generating documentation with Doxygen:</h3> 106 <p>The libray documentation can be generated directly from the source codes using Doxygen tool: </p> 107 <pre class="fragment"># in build directory 108 make doc 109 google-chrome doc/html/index.html 110 </pre><h2>CMake Options <a class="anchor" id="CMake"></a></h2> 111 <p>The json-c library is built with <a href="https://cmake.org/cmake-tutorial/">CMake</a>, which can take a few options.</p> 112 <table class="doxtable"> 113 <tr> 114 <th>Variable </th><th>Type </th><th>Description</th></tr> 115 <tr> 116 <td>CMAKE_INSTALL_PREFIX </td><td>String </td><td>The install location. </td></tr> 117 <tr> 118 <td>CMAKE_BUILD_TYPE </td><td>String </td><td>Defaults to "debug". </td></tr> 119 <tr> 120 <td>BUILD_SHARED_LIBS </td><td>Bool </td><td>The default build generates a dynamic (dll/so) library. Set this to OFF to create a static library only. </td></tr> 121 <tr> 122 <td>BUILD_STATIC_LIBS </td><td>Bool </td><td>The default build generates a static (lib/a) library. Set this to OFF to create a shared library only. </td></tr> 123 <tr> 124 <td>DISABLE_STATIC_FPIC </td><td>Bool </td><td>The default builds position independent code. Set this to OFF to create a shared library only. </td></tr> 125 <tr> 126 <td>DISABLE_BSYMBOLIC </td><td>Bool </td><td>Disable use of -Bsymbolic-functions. </td></tr> 127 <tr> 128 <td>DISABLE_THREAD_LOCAL_STORAGE </td><td>Bool </td><td>Disable use of Thread-Local Storage (HAVE___THREAD). </td></tr> 129 <tr> 130 <td>DISABLE_WERROR </td><td>Bool </td><td>Disable use of -Werror. </td></tr> 131 <tr> 132 <td>ENABLE_RDRAND </td><td>Bool </td><td>Enable RDRAND Hardware RNG Hash Seed. </td></tr> 133 <tr> 134 <td>ENABLE_THREADING </td><td>Bool </td><td>Enable partial threading support. </td></tr> 135 <tr> 136 <td>OVERRIDE_GET_RANDOM_SEED </td><td>String </td><td>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. </td></tr> 137 </table> 138 <p>Pass these options as <code>-D</code> on CMake's command-line. </p> 139 <pre class="fragment"># build a static library only 140 cmake -DBUILD_SHARED_LIBS=OFF .. 141 </pre><h3>Building with partial threading support</h3> 142 <p>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 <a class="el" href="json__object_8h.html#a675aa3a9cced685dbfd1c1a770a0c3e4">json_object_get()</a> and <a class="el" href="json__object_8h.html#afabf61f932cd64a4122ca8092452eed5">json_object_put()</a>.</p> 143 <p>Since this may have a performance impact, of at least 3x slower according to <a href="https://stackoverflow.com/a/11609063,">https://stackoverflow.com/a/11609063,</a> it is disabled by default. You may turn it on by adjusting your cmake command with: -DENABLE_THREADING=ON</p> 144 <p>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.</p> 145 <h3>cmake-configure wrapper script</h3> 146 <p>For those familiar with the old autoconf/autogen.sh/configure method, there is a <code>cmake-configure</code> wrapper script to ease the transition to cmake. </p> 147 <pre class="fragment">mkdir build 148 cd build 149 ../cmake-configure --prefix=/some/install/path 150 make 151 </pre><p>cmake-configure can take a few options.</p> 152 <table class="doxtable"> 153 <tr> 154 <th>options </th><th>Description</th></tr> 155 <tr> 156 <td>prefix=PREFIX </td><td>install architecture-independent files in PREFIX </td></tr> 157 <tr> 158 <td>enable-threading </td><td>Enable code to support partly multi-threaded use </td></tr> 159 <tr> 160 <td>enable-rdrand </td><td>Enable RDRAND Hardware RNG Hash Seed generation on supported x86/x64 platforms. </td></tr> 161 <tr> 162 <td>enable-shared </td><td>build shared libraries [default=yes] </td></tr> 163 <tr> 164 <td>enable-static </td><td>build static libraries [default=yes] </td></tr> 165 <tr> 166 <td>disable-Bsymbolic </td><td>Avoid linking with -Bsymbolic-function </td></tr> 167 <tr> 168 <td>disable-werror </td><td>Avoid treating compiler warnings as fatal errors </td></tr> 169 </table> 170 <h2>Testing: <a class="anchor" id="testing"></a></h2> 171 <p>By default, if valgrind is available running tests uses it. That can slow the tests down considerably, so to disable it use: </p> 172 <pre class="fragment">export USE_VALGRIND=0 173 </pre><p>To run tests a separate build directory is recommended: </p> 174 <pre class="fragment">mkdir build-test 175 cd build-test 176 # VALGRIND=1 causes -DVALGRIND=1 to be passed when compiling code 177 # which uses slightly slower, but valgrind-safe code. 178 VALGRIND=1 cmake .. 179 make 180 181 make test 182 # By default, if valgrind is available running tests uses it. 183 make USE_VALGRIND=0 test # optionally skip using valgrind 184 </pre><p>If a test fails, check <code>Testing/Temporary/LastTest.log</code>, <code>tests/testSubDir/${testname}/${testname}.vg.out</code>, and other similar files. If there is insufficient output try: </p> 185 <pre class="fragment">VERBOSE=1 make test 186 </pre><p>or </p> 187 <pre class="fragment">JSONC_TEST_TRACE=1 make test 188 </pre><p>and check the log files again.</p> 189 <h2>Building on Unix and Windows with <code>vcpkg</code> <a class="anchor" id="buildvcpkg"></a></h2> 190 <p>You can download and install JSON-C using the <a href="https://github.com/Microsoft/vcpkg/">vcpkg</a> dependency manager: </p> 191 <pre class="fragment">git clone https://github.com/Microsoft/vcpkg.git 192 cd vcpkg 193 ./bootstrap-vcpkg.sh 194 ./vcpkg integrate install 195 vcpkg install json-c 196 </pre><p>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 <a href="https://github.com/Microsoft/vcpkg">create an issue or pull request</a> on the vcpkg repository.</p> 197 <h2>Linking to <code>libjson-c</code> <a class="anchor" id="linking"></a></h2> 198 <p>If your system has <code>pkgconfig</code>, then you can just add this to your <code>makefile</code>: </p> 199 <pre class="fragment">CFLAGS += $(shell pkg-config --cflags json-c) 200 LDFLAGS += $(shell pkg-config --libs json-c) 201 </pre><p>Without <code>pkgconfig</code>, you would do something like this: </p> 202 <pre class="fragment">JSON_C_DIR=/path/to/json_c/install 203 CFLAGS += -I$(JSON_C_DIR)/include/json-c 204 LDFLAGS+= -L$(JSON_C_DIR)/lib -ljson-c 205 </pre><h2>Using json-c <a class="anchor" id="using"></a></h2> 206 <p>To use json-c you can either include <a class="el" href="json_8h.html" title="A convenience header that may be included instead of other individual ones.">json.h</a>, or preferrably, one of the following more specific header files:</p> 207 <ul> 208 <li><a class="el" href="json__object_8h.html" title="Core json-c API. Start here, or with json_tokener.h.">json_object.h</a> - Core types and methods.</li> 209 <li><a class="el" href="json__tokener_8h.html" title="Methods to parse an input string into a tree of json_object objects.">json_tokener.h</a> - Methods for parsing and serializing json-c object trees.</li> 210 <li><a class="el" href="json__pointer_8h.html" title="JSON Pointer (RFC 6901) implementation for retrieving objects from a json-c object tree...">json_pointer.h</a> - JSON Pointer (RFC 6901) implementation for retrieving objects from a json-c object tree.</li> 211 <li><a class="el" href="json__object__iterator_8h.html" title="An API for iterating over json_type_object objects, styled to be familiar to C++ programmers. Unlike json_object_object_foreach() and json_object_object_foreachC(), this avoids the need to expose json-c internals like lh_entry.">json_object_iterator.h</a> - Methods for iterating over single json_object instances. (See also <code><a class="el" href="json__object_8h.html#acf5f514a9e0061c10fc08055762639ee">json_object_object_foreach()</a></code> in <a class="el" href="json__object_8h.html" title="Core json-c API. Start here, or with json_tokener.h.">json_object.h</a>)</li> 212 <li><a class="el" href="json__visit_8h.html" title="Methods for walking a tree of objects.">json_visit.h</a> - Methods for walking a tree of json-c objects.</li> 213 <li><a class="el" href="json__util_8h.html" title="Miscllaneous utility functions and macros.">json_util.h</a> - Miscelleanous utility functions.</li> 214 </ul> 215 <p>For a full list of headers see <a href="http://json-c.github.io/json-c/json-c-current-release/doc/html/files.html">files.html</a></p> 216 <p>The primary type in json-c is json_object. It describes a reference counted tree of json objects which are created by either parsing text with a <a class="el" href="structjson__tokener.html">json_tokener</a> (i.e. <code><a class="el" href="json__tokener_8h.html#a61679f178111963a9ffa3c8179553f7a">json_tokener_parse_ex()</a></code>), or by creating (with <code><a class="el" href="json__object_8h.html#a68c383f54544fca19b5f2425be397600">json_object_new_object()</a></code>, <code><a class="el" href="json__object_8h.html#ae92f0770fb4b3c884ce35de52d3d7de8">json_object_new_int()</a></code>, etc...) and adding (with <code><a class="el" href="json__object_8h.html#a27bd808a022251059a43f1f6370441cd">json_object_object_add()</a></code>, <code><a class="el" href="json__object_8h.html#a18cdd9a7455e09f36cdf6e5756b7f586">json_object_array_add()</a></code>, etc...) them individually. Typically, every object in the tree will have one reference, from it's parent. When you are done with the tree of objects, you call <a class="el" href="json__object_8h.html#afabf61f932cd64a4122ca8092452eed5">json_object_put()</a> on just the root object to free it, which recurses down through any child objects calling <a class="el" href="json__object_8h.html#afabf61f932cd64a4122ca8092452eed5">json_object_put()</a> on each one of those in turn.</p> 217 <p>You can get a reference to a single child (<code><a class="el" href="json__object_8h.html#a1a097805abb53b4c8a60d573730a8939">json_object_object_get()</a></code> or <code><a class="el" href="json__object_8h.html#a676711a76545d4ec65cc75f100f5fd19">json_object_array_get_idx()</a></code>) and use that object as long as its parent is valid. If you need a child object to live longer than its parent, you can increment the child's refcount (<code><a class="el" href="json__object_8h.html#a675aa3a9cced685dbfd1c1a770a0c3e4">json_object_get()</a></code>) to allow it to survive the parent being freed or it being removed from its parent (<code><a class="el" href="json__object_8h.html#ac6605fdafca20bd5d33c84f4f80a3bda">json_object_object_del()</a></code> or <code><a class="el" href="json__object_8h.html#a722eca9f578704d3af38b97549242c1f">json_object_array_del_idx()</a></code>)</p> 218 <p>When parsing text, the <a class="el" href="structjson__tokener.html">json_tokener</a> object is independent from the json_object that it returns. It can be allocated (<code><a class="el" href="json__tokener_8h.html#a5ac7e2c350bc592cf2fa7b9935b00ef5">json_tokener_new()</a></code>) used ones or multiple times (<code><a class="el" href="json__tokener_8h.html#a61679f178111963a9ffa3c8179553f7a">json_tokener_parse_ex()</a></code>, and freed (<code><a class="el" href="json__tokener_8h.html#a887c4661906fc6b36cc366304e522534">json_tokener_free()</a></code>) while the json_object objects live on.</p> 219 <p>A json_object tree can be serialized back into a string with <code><a class="el" href="json__object_8h.html#a9db613127bd4ef7db42307e43a85fc1b">json_object_to_json_string_ext()</a></code>. The string that is returned is only valid until the next "to_json_string" call on that same object. Also, it is freed when the json_object is freed. </p> 220 </div></div><!-- contents --> 221 <!-- start footer part --> 222 <hr class="footer"/><address class="footer"><small> 223 Generated on Sun Jul 26 2020 15:11:19 for json-c by  <a href="http://www.doxygen.org/index.html"> 224 <img class="footer" src="doxygen.png" alt="doxygen"/> 225 </a> 1.8.2 226 </small></address> 227 </body> 228 </html>
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