A simple class for parsing JSON data into a QVariant hierarchy and vice versa.
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gaudecker Merge pull request #46 from gitantonio/builders
Added Builders + Pretty-print serialization
Latest commit 6f181e4 Feb 12, 2018


The qt-json project is a simple collection of functions for parsing and serializing JSON data to and from QVariant hierarchies.

NOTE: Qt5 introduced a native JSON object class. If you are targeting Qt5, you should use that instead.


Parsing JSON

The parser is really easy to use. Let's say we have the following QString of JSON data:

  "encoding" : "UTF-8",
  "plug-ins" : [
  "indent" : {
    "length" : 3,
    "use_space" : true

We would first call the parse-function:

#include "json.h"

bool ok;
// json is a QString containing the JSON data
QtJson::JsonObject result = QtJson::parse(json, ok).toMap();

if(!ok) {
  qFatal("An error occurred during parsing");

Assuming the parser completed without errors, we can then go through the hierarchy:

qDebug() << "encoding:" << result["encoding"].toString();
qDebug() << "plugins:";

foreach(QVariant plugin, result["plug-ins"].toList()) {
    qDebug() << "  -" << plugin.toString();

QtJson::JsonObject nested = result["indent"].toMap();
qDebug() << "length:" << nested["length"].toInt();
qDebug() << "use_space:" << nested["use_space"].toBool();

The previous code would print out the following:

encoding: "UTF-8"
  - "python"
  - "c++"
  - "ruby"
length: 3
use_space: true

Serializing JSON

To write JSON data from Qt object is as simple as creating and assigning data to a QVariantMap/JsonObject:

QtJson::JsonObject contributor;
contributor["name"] = "Luis Gustavo";
contributor["age"] = 22;

QByteArray data = QtJson::serialize(contributor);

The byte array 'data' contains valid JSON data:

  "name": "Luis Gustavo",
  "age": 22

Serializing JSON pretty-print

By default, the serialization will create a minified version, like following:

{"name":"Luis Gustavo","age":22}

If you are debugging or logging, you may prefer to enable pretty-print mode globally, before serialize:


QByteArray data = QtJson::serialize(contributor);
// ...
QByteArray data = QtJson::serialize(other_contributor);

Obviously, you can disable it with:


After creating the QVariantMap, you can create a QVariantList/JsonArray and append the QVariantMaps.

QtJson::JsonObject friend1, friend2, friend3;
friend1["id"] = 1;
friend1["name"] = "Mackenzie Hamphrey";

friend2["id"] = 2;
friend2["name"] = "Melanie Molligan";

friend3["id"] = 3;
friend3["name"] = "Sydney Calhoun";

QtJson::JsonArray friends;

QtJson::JsonObject obj;
obj["friends"] = friends;

This way you create a nested structure:

    "friends": [
            "id": 1,
            "name": "MackenzieHamphrey"
            "id": 2,
            "name": "MelanieMolligan"
            "id": 3,
            "name": "SydneyCalhoun"

If you continue this process recursively, you nest more levels into the JSON structure.

Using Builders

For simplicity you can use builders, if you prefer.

For example, create a JsonObject:

QtJson::JsonObject json = QtJson::objectBuilder()
    ->set("field_1", 10)
    ->set("field_2", "A string")
    ->set("field_3", true)
    ->set("field_4", QtJson::objectBuilder()
        ->set("sub_field_1", 10.4)
        ->set("sub_field_n", "Another string")

Or create a JsonArray:

QtJson::JsonArray json = QtJson::arrayBuilder()
    ->add("anything else")

Take a look at this example that rewrite the previous one:

QtJson::JsonObject obj = QtJson::objectBuilder()
    ->set("friends", QtJson::arrayBuilder()
            ->set("id", 1)
            ->set("name", "Mackenzie Hamphrey")
            ->set("id", 2)
            ->set("name", "Melanie Molligan")
            ->set("id", 3)
            ->set("name", "Sydney Calhoun")


Send in a pull request and bug the maintainer until it gets merged and published. Make sure to add yourself to AUTHORS.