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# cJSON Ultralightweight JSON parser in ANSI C. ## Table of contents * [License](#license) * [Usage](#usage) * [Welcome to cJSON](#welcome-to-cjson) * [Building](#building) * [Some JSON](#some-json) * [Here's the structure](#heres-the-structure) * [Caveats](#caveats) * [Enjoy cJSON!](#enjoy-cjson) ## License MIT License > Copyright (c) 2009-2017 Dave Gamble and cJSON contributors > > Permission is hereby granted, free of charge, to any person obtaining a copy > of this software and associated documentation files (the "Software"), to deal > in the Software without restriction, including without limitation the rights > to use, copy, modify, merge, publish, distribute, sublicense, and/or sell > copies of the Software, and to permit persons to whom the Software is > furnished to do so, subject to the following conditions: > > The above copyright notice and this permission notice shall be included in > all copies or substantial portions of the Software. > > THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR > IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, > FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE > AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER > LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, > OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN > THE SOFTWARE. ## Usage ### Welcome to cJSON. cJSON aims to be the dumbest possible parser that you can get your job done with. It's a single file of C, and a single header file. JSON is described best here: http://www.json.org/ It's like XML, but fat-free. You use it to move data around, store things, or just generally represent your program's state. As a library, cJSON exists to take away as much legwork as it can, but not get in your way. As a point of pragmatism (i.e. ignoring the truth), I'm going to say that you can use it in one of two modes: Auto and Manual. Let's have a quick run-through. I lifted some JSON from this page: http://www.json.org/fatfree.html That page inspired me to write cJSON, which is a parser that tries to share the same philosophy as JSON itself. Simple, dumb, out of the way. ### Building There are several ways to incorporate cJSON into your project. #### copying the source Because the entire library is only one C file and one header file, you can just copy `cJSON.h` and `cJSON.c` to your projects source and start using it. cJSON is written in ANSI C (C89) in order to support as many platforms and compilers as possible. #### CMake With CMake, cJSON supports a full blown build system. This way you get the most features. CMake with an equal or higher version than 2.8.5 is supported. With CMake it is recommended to do an out of tree build, meaning the compiled files are put in a directory separate from the source files. So in order to build cJSON with CMake on a Unix platform, make a `build` directory and run CMake inside it. ``` mkdir build cd build cmake .. ``` This will create a Makefile and a bunch of other files. You can then compile it: ``` make ``` And install it with `make install` if you want. By default it installs the headers `/usr/local/include/cjson` and the libraries to `/usr/local/lib`. It also installs files for pkg-config to make it easier to detect and use an existing installation of CMake. And it installs CMake config files, that can be used by other CMake based projects to discover the library. You can change the build process with a list of different options that you can pass to CMake. Turn them on with `On` and off with `Off`: * `-DENABLE_CJSON_TEST=On`: Enable building the tests. (on by default) * `-DENABLE_CJSON_UTILS=On`: Enable building cJSON_Utils. (off by default) * `-DENABLE_TARGET_EXPORT=On`: Enable the export of CMake targets. Turn off if it makes problems. (on by default) * `-DENABLE_CUSTOM_COMPILER_FLAGS=On`: Enable custom compiler flags (currently for Clang and GCC). Turn off if it makes problems. (on by default) * `-DENABLE_VALGRIND=On`: Run tests with [valgrind](http://valgrind.org). (off by default) * `-DENABLE_SANITIZERS=On`: Compile cJSON with [AddressSanitizer](https://github.com/google/sanitizers/wiki/AddressSanitizer) and [UndefinedBehaviorSanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html) enabled (if possible). (off by default) * `-DBUILD_SHARED_LIBS=On`: Build the shared libraries. (on by default) * `-DCMAKE_INSTALL_PREFIX=/usr`: Set a prefix for the installation. If you are packaging cJSON for a distribution of Linux, you would probably take these steps for example: ``` mkdir build cd build cmake .. -DENABLE_CJSON_UTILS=On -DENABLE_CJSON_TEST=Off -DCMAKE_INSTALL_PREFIX=/usr make make DESTDIR=$pkgdir install ``` #### Makefile If you don't have CMake available, but still have GNU make. You can use the makefile to build cJSON: Run this command in the directory with the source code and it will automatically compile static and shared libraries and a little test program. ``` make all ``` If you want, you can install the compiled library to your system using `make install`. By default it will install the headers in `/usr/local/include/cjson` and the libraries in `/usr/local/lib`. But you can change this behavior by setting the `PREFIX` and `DESTDIR` variables: `make PREFIX=/usr DESTDIR=temp install`. ### Some JSON: ```json { "name": "Jack (\"Bee\") Nimble", "format": { "type": "rect", "width": 1920, "height": 1080, "interlace": false, "frame rate": 24 } } ``` Assume that you got this from a file, a webserver, or magic JSON elves, whatever, you have a `char *` to it. Everything is a `cJSON` struct. Get it parsed: ```c cJSON * root = cJSON_Parse(my_json_string); ``` This is an object. We're in C. We don't have objects. But we do have structs. What's the framerate? ```c cJSON *format = cJSON_GetObjectItemCaseSensitive(root, "format"); cJSON *framerate_item = cJSON_GetObjectItemCaseSensitive(format, "frame rate"); double framerate = 0; if (cJSON_IsNumber(framerate_item)) { framerate = framerate_item->valuedouble; } ``` Want to change the framerate? ```c cJSON *framerate_item = cJSON_GetObjectItemCaseSensitive(format, "frame rate"); cJSON_SetNumberValue(framerate_item, 25); ``` Back to disk? ```c char *rendered = cJSON_Print(root); ``` Finished? Delete the root (this takes care of everything else). ```c cJSON_Delete(root); ``` That's AUTO mode. If you're going to use Auto mode, you really ought to check pointers before you dereference them. If you want to see how you'd build this struct in code? ```c cJSON *root; cJSON *fmt; root = cJSON_CreateObject(); cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble")); cJSON_AddItemToObject(root, "format", fmt = cJSON_CreateObject()); cJSON_AddStringToObject(fmt, "type", "rect"); cJSON_AddNumberToObject(fmt, "width", 1920); cJSON_AddNumberToObject(fmt, "height", 1080); cJSON_AddFalseToObject (fmt, "interlace"); cJSON_AddNumberToObject(fmt, "frame rate", 24); ``` Hopefully we can agree that's not a lot of code? There's no overhead, no unnecessary setup. Look at `test.c` for a bunch of nice examples, mostly all ripped off the [json.org](http://json.org) site, and a few from elsewhere. What about manual mode? First up you need some detail. Let's cover how the `cJSON` objects represent the JSON data. cJSON doesn't distinguish arrays from objects in handling; just type. Each `cJSON` has, potentially, a child, siblings, value, a name. * The `root` object has: *Object* Type and a Child * The Child has name "name", with value "Jack ("Bee") Nimble", and a sibling: * Sibling has type *Object*, name "format", and a child. * That child has type *String*, name "type", value "rect", and a sibling: * Sibling has type *Number*, name "width", value 1920, and a sibling: * Sibling has type