Installation

Make sure you already have Git, GCC or Clang, CMake, GNU Make installed on your system.

Then clone, build and install with the following commands:

git clone https://github.com/nlohmann/json
cd json
mkdir build && cd build
cmake..
make
sudo make install

It will be Copied/Installed in directories similar to the ones below:

-- Install configuration: ""
-- Up-to-date: /usr/local/include
-- Installing: /usr/local/include/nlohmann
-- Installing: /usr/local/include/nlohmann/json.hpp
-- Installing: /usr/local/lib64/cmake/nlohmann_json/nlohmann_jsonConfig.cmake
-- Installing: /usr/local/lib64/cmake/nlohmann_json/nlohmann_jsonConfigVersion.cmake
-- Installing: /usr/local/lib64/cmake/nlohmann_json/nlohmann_jsonTargets.cmake
-- Installing: /usr/local/lib64/pkgconfig/nlohmann_json.pc

Basic usage example

To create a basic JSON.

vim hello-json.cpp

#include <iostream>
#include <nlohmann/json.hpp>

int main(){
  nlohmann::json j;
  j.push_back("Hello");
  j.emplace_back("World");
  std::cout << j << '\n';
}

g++ hello-json.cpp and run: ./a

Possible output:

["Hello","World"]

Printing only the first element of JSON:

#include <iostream>
#include <nlohmann/json.hpp>

int main(){
  nlohmann::json j;
  j.push_back("Hello");
  j.emplace_back("World");
  std::cout << j[0] << '\n';
}

Possible output: "Hello"

Parsing

Example of a example.json JSON file:

{
  "number": 42,
  "website": "Terminal Root",
  "author": "Marcos Oliveira",
  "parsing": true,
  "details": {
    "tutorial": "json C++",
    "id": 1
  },
  "other": null
}

Print all content:

#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>

int main(){
  std::ifstream file("./example.json");
  nlohmann::json j;
  file >> j;
  std::cout << j << '\n';
}

Possible output, note that the display has been changed to alphabetical order:

{"author":"Marcos Oliveira","details":{"id":1,"tutorial":"json C++"},"number":42,"other":null,"parsing":true," website":"Terminal Root"}

Print content with formatting:

#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>

int main(){
  std::ifstream file("./example.json");
  nlohmann::json j;
  file >> j;
  std::cout << std::setw(2) << j << '\n';
}

Possible output,note that the display has been changed to alphabetical order :

{
  "author": "Marcos Oliveira",
  "details": {
    "id": 1,
    "tutorial": "json C++"
  },
  "number": 42,
  "other": null,
  "parsing": true,
  "website": "Terminal Root"
}

Print only website content

#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>

int main(){
  std::ifstream file("./example.json");
  nlohmann::json j;
  file >> j;
  std::string website = j["website"];
  std::cout << website << '\n';
}

Possible output: Terminal Root .

Print the contents of {"details": {"tutorial"}}:

#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>

int main(){
  std::ifstream file("./example.json");
  nlohmann::json j;
  file >> j;
  std::string jstr = j["details"]["tutorial"];
  std::cout << jstr << '\n';
}