json-cpp

A library to use JSON objects in C++.

This library supports all the basic JSON types: null, boolean, number, string, array and object.

The types used in this library to store the datas are defined in the src/TypesDef.hpp file as follows:

null    -> nullptr
boolean -> bool
integer -> int
float   -> float
string  -> std::string
array   -> std::vector<json>
object  -> std::map<std::string, json>

Run the tests

To test the library, you can first navigate to the tests directory:

cd tests

Then, you can build the project with:

mkdir build
cd build
cmake ..
make
cd ..

Finally, you can run the tests with:

./build/my_app

If you want to modify the tests to test your own code or view some examples, you can edit the main.cpp file.

The CMakelists.txt file in the tests/ directory is a great example of how to compile the library in your own project.

Usage examples

Here are some examples of how to use the library.

For all the examples, you first need to include the library:

#include <json/json.hpp>
using namespace jsoncpp;

Create a JSON object

json test;

By default, the json object is set to null.

Create a JSON object with a value

json test = true;
// or
json test = 42;
// or
json test = 42.42;
// or
json test = "Hello World!";

If you want to set it to an empty object, you can do:

json test = Object();

Or to an empty array:

json test = Array();

Add a value to a JSON object

test["key1"] = "value1";
test["key2"] = "value2";
test["key3"] = "value3";

Add a value to a JSON array

test.push("value1");
test.push("value2");
test.push("value3");

Create JSON object from a string

json test = json::parse(R"(
    {
        "key1": "value1",
        "key2": "value2",
        "key3": "value3"
    }
)");

Read from a JSON file

std::ifstream input("test.json");
json test = json::parse(input);

Write to a JSON file

std::ofstream output("test_write.json");
output << test;

Result:

{"key1": "value1","key2": "value2","key3": "value3"}

Or with indentation:

std::ofstream output("test_write.json");
output << test.toString(4);

Result:

{
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
}

Convert to a string

std::string str = test.toString();

Or with indentation:

std::string str = test.toString(4);

Get a value from a JSON

bool &value = test;
// or
int &value = test;
// or
float &value = test;
// or
std::string &value = test;
// or
std::vector<json> &value = test;
// or
std::map<std::string, json> &value = test;

Get a value from a JSON object

bool &value = test["key1"];
// or
int &value = test["key1"];
// or
float &value = test["key1"];
// or
std::string &value = test["key1"];
// or
std::vector<json> &value = test["key1"];
// or
std::map<std::string, json> &value = test["key1"];

Get a value from a JSON array

bool &value = test[0];
// or
int &value = test[0];
// or
float &value = test[0];
// or
std::string &value = test[0];
// or
std::vector<json> &value = test[0];
// or
std::map<std::string, json> &value = test[0];

Operations on objects

A lot of methods are available to manipulate JSON objects. Here are some examples:

json test = Object();
test["key1"] = "value1";
test.insert("key2", "value2");
if (test.contains("key1"))
    std::cout << "key1 exists" << std::endl;
test.erase("key1");
test.at("key2") = "value3";
std::cout << test.size() << std::endl;
test.clear();
if (test.empty())
    std::cout << "test is empty" << std::endl;

Operations on arrays

A lot of methods are available to manipulate JSON arrays. Here are some examples:

json test = Array();
test.push("value1");
test.push("value2");
test.insert(1, "value4");
test.erase(1);
test.at(1) = "value5";
test.front() = "front";
test.back() = "back";
std::cout << test.size() << std::endl;
test.clear();
if (test.empty())
    std::cout << "test is empty" << std::endl;

License

This project is licensed under the MIT License - see the LICENSE file for details.