json-cpp

Lightweight JSON parser and writer for C++

• Installation
• Usage
  • Loading Data
  • Editing Data
  • Outputting Data

installation

There are two ways to include this library.

1. Drag the contents of the include directory to the include directory of your project.
2. Or, simply place the json.hpp file in your project with the other source files.

And then in your project header or source files, use the following include statement:

#include <jsoncpp/json.hpp> // if the library is in an include directory
#include "jsoncpp/json.hpp" // if the library is with the project source files

usage

loading data

You can load data in 3 ways:

1. Parse the data from a string:

jsoncpp::parse("{\"employees\": []}");

2. Load the data from a file:

jsoncpp::read("data.json");

3. Initialize a json object in code

jsoncpp::json d = {
    { "employees", {
    	{
        	{ "name", "Michael" },
            { "age", 32 },
            { "manager", true },
            { "SSN", jsoncpp::null }
        }
    }}
};

/*
This would translate to in JSON:
{
    "employees": [
    	{
        	"name": "Michael",
            "age": 32,
            "manager": true
        }
    ]
}
*/

note that key-value pairs are separated by commas rather than colons since a pair in C++ can be represented as a list of two values

editing data

You can use the assignment operator to set values.

// null values
jsoncpp::json n = jsoncpp::null;

// strings
jsoncpp::json s = "This is a string";

// numbers
jsoncpp::json d = 3.1415;
jsoncpp::json i = 3;
jsoncpp::json f = 3.1415f;

// boolean
jsoncpp::json b = true;

// lists
jsoncpp::json l = {
    5,
    "hello",
    false,
    {
    	6,
        true
    }
};

/*
This would translate to in JSON:
[
    5,
    "hello",
    false,
    [
    	6,
        true
    ]
]
*/

// objects (dictionaries)
jsoncpp::json o = {
    { "employees", {
    	{
        	{ "name", "Michael" },
            { "age", 32 },
            { "manager", true }
        }
    }}
};

Using the operators + and += are defined for strings, numbers, and lists.

// strings
jsoncpp::json s = "Hello,";
jsoncpp::json s2 = " world";
jsoncpp::json s3 = s + s2;
s3 += "!"; // s3 = "Hello, world!"

// numbers
jsoncpp::json d = 0;
for (int i = 1; i < INT_MAX; i++) {
	d += 4 * pow(-1, i + 1) / (2 * i - 1);
}
// d = 3.1415...

// lists
jsoncpp::json l = { 1, 2, 3, 4 };
l += 5; // l = { 1, 2, 3, 4, 5 }
// in order to add all elements of a list to a list
l.addAll({6, 7, 8, 9, 10}); // l = { 1, ..., 10 }

Using the operator [] is defined for lists and objects

jsoncpp::json l = { 1, 2, 3, 4 };
l[3] = 18; // l = { 1, 2, 3, 18 };

jsoncpp::json d = {
	{ "name", "Michael" }
};
d["name"] = "Stalin";
d["age"] = INT_MAX;
//d = { "name": "Stalin", "age": 2147483647 }

outputting data

To access the value of a json class:

// string
jsoncpp::json s = "Hello";
s.val<std::string>(); // "Hello";
s.val<const char*>(); // "Hello";

// float
jsoncpp::json f = 3.1415;
n.val<double>(); // 3.1415
n.val<float>(); // 3.1415f
n.val<int>(); // 3

// int
jsoncpp::json i = 3;
n.val<int>(); // 3
n.val<float>(); // 3.0f
n.val<double>(); // 3.0

// bool
jsoncpp::json b = true;
b.val<bool>(); // true

To get the string representation of a json class:

jsoncpp::json o = {
    { "employees", {
    	{
            { "name", "Michael" },
            { "age", 32 },
            { "manager", true },
            { "SSN", null }
        }
    }}
};

// to get the string without spacing
o.dump(); // {"employees":[{"name":"Michael","age":32,"manager":true,"SSN":null}]}

// to pretty print
o.dump(4); // 4 is the tab spacing
/*
{
    "employees": [
    	{
        	"name": "Michael",
            "age": 32,
            "manager": true,
            "SSN": null
        }
    ]
}
*/

To write to a file:

jsoncpp::json o;

// without pretty printing
o.dump("data.json");

// with pretty printing
o.dump("data.json", 4);