Using Jsoncpp to read and write JSON data in a C + + environment

JSON (JavaScript object Notation, JS tag) is a lightweight data interchange format. Typically used for data exchange or storage.

Jsoncpp is a C + + language-based open source Library for C + + program JSON data read and write operations.

Jsoncpp is an open source library

: Https://github.com/open-source-parsers/jsoncpp

Document Address: http://open-source-parsers.github.io/jsoncpp-docs/doxygen/index.html

Use

An official integration solution: https://github.com/open-source-parsers/jsoncpp/wiki/Amalgamated

The simplest way to do this is to execute the project root directory in thepython脚本，构建头文件和源文件。

1. Enter the Jsoncpp project root directory in the console where the Python environment is installed,

2. Execute the command:

Python amalgamate.py

3. Copy the generated dist directory to your project, where the package source jsoncpp.cpp and header filesjson.h、json-forwards.h。

Basic classes and methods

jsoncppneed to include header files when using libraries#include <json/json.h>（包含目录根据需要修改）

Method namespaces: Json

Common classes

Value: Used to store JSON data

Charreader: Abstract class for reading JSON data from a string

Implementation of the Charreaderbuilder:charreader class to read data from the standard input stream

Demo

Defines a JSON data structure and outputs it

Json::value Jsonroot;//defining the root nodeJson::value Jsonitem;//define a child objectjsonitem["item1"] =" One";//Add Datajsonitem["item2"] =2;jsonroot.append (jsonitem);Jsonitem.clear ();//Clear Jsonitem
jsonitem["item1.0"] = 1.0; jsonitem["item2.0"] = 2.0;       Jsonroot["Item"] =Jsonitem;cout<< jsonroot.tostyledstring () << Endl;//Output to console

Writing JSON to a file

// standard output stream Ofs.open ("sample.json"// Create file // output Ofs.close ();

Reading JSON data from a file

ifstream IFS;//Standard input stream Ifs.open ("sample. JSON");
Jsonroot.clear ();
Json::charreaderbuilder builder;builder["collectcomments"false ; jsoncpp_string errs; if (!parsefromstream (Builder, IFS, &jsonroot, &errs)//Read data from IFS to jsonroot{    return ;}

Reading JSON data from a string

string jsonstr = jsonroot.tostyledstring ();//json string jsonroot.clear ();
Json::charreaderbuilder builder;builder["collectcomments"false; Jsoncpp_string errs; Json::charreader* reader = builder.newcharreader (); if (!reader->parse (Jsonstr.data (), Jsonstr.data () + jsonstr.size (), &jsonroot, &errs))// Read data from Jsonstr to jsonroot{    return;}

Gets the key-value pairs in the JSON

 for 0; I < jsonroot.size (); i++) {    for (auto sub= jsonroot[i].begin (); Sub! = Jsonroot[i].end (); sub++)    {          "  " << jsonroot[i][sub.name ()] << Endl;    }}

Using Jsoncpp to read and write JSON data in a C + + environment