如何扁平化包含6种基础类型的多维嵌套QJsonValue结构？

需要实现一个工具方法，把包含object、array、bool、double、String、Null这6种基础类型的多维嵌套QJsonValue展开为扁平化的“键路径-值”结构，键路径用.分隔层级，所有值统一转为字符串格式，示例如下：

输入示例 #

{
    "date": 1681693886,
    "online": true,
    "none": null,
    "list": {
        "arr": [
            60,
            100,
            100,
            100,
            100,
            100
        ],
        "multiArr": [
            ["hi", "my", "name"],
            ["is", "unknown"],
            [{"first": 0}, {"last": 100}]
        ],
        "num": 60
    }
}

预期输出 #

key = "date",                     value = "1.68169e+09"
key = "list.arr.0",               value = "60"
key = "list.arr.1",               value = "100"
key = "list.arr.2",               value = "100"
key = "list.arr.3",               value = "100"
key = "list.arr.4",               value = "100"
key = "list.arr.5",               value = "100"
key = "list.multiArr.0.0",        value = "hi"
key = "list.multiArr.0.1",        value = "my"
key = "list.multiArr.0.2",        value = "name"
key = "list.multiArr.1.0",        value = "is"
key = "list.multiArr.1.1",        value = "unknown"
key = "list.multiArr.2.0.first",  value = "0"
key = "list.multiArr.2.1.last",   value = "100"
key = "list.num",                 value = "60"
key = "none",                     value = "null"
key = "online",                   value = "true"

实现思路与代码 #

核心是通过递归遍历处理不同类型的QJsonValue，根据类型生成对应的键路径和字符串值：

#include <QJsonValue>
#include <QJsonObject>
#include <QJsonArray>
#include <QMap>
#include <QString>

// 递归扁平化QJsonValue，结果存入map中，key为路径，value为字符串化的值
void flattenJson(const QJsonValue &value, const QString &currentPath, QMap<QString, QString> &result) {
    switch (value.type()) {
        case QJsonValue::Null:
            result[currentPath] = "null";
            break;
        case QJsonValue::Bool:
            result[currentPath] = value.toBool() ? "true" : "false";
            break;
        case QJsonValue::Double:
            // 按照示例格式，保留5位小数的科学计数法
            result[currentPath] = QString::number(value.toDouble(), 'e', 5);
            break;
        case QJsonValue::String:
            result[currentPath] = value.toString();
            break;
        case QJsonValue::Object: {
            QJsonObject obj = value.toObject();
            for (auto it = obj.constBegin(); it != obj.constEnd(); ++it) {
                QString newPath = currentPath.isEmpty() ? it.key() : currentPath + "." + it.key();
                flattenJson(it.value(), newPath, result);
            }
            break;
        }
        case QJsonValue::Array: {
            QJsonArray arr = value.toArray();
            for (int i = 0; i < arr.size(); ++i) {
                QString newPath = currentPath.isEmpty() ? QString::number(i) : currentPath + "." + QString::number(i);
                flattenJson(arr[i], newPath, result);
            }
            break;
        }
        default:
            // 处理未定义类型，可根据需求补充
            result[currentPath] = "undefined";
            break;
    }
}

// 对外接口，输入QJsonValue返回扁平化的键值对map
QMap<QString, QString> flattenQJsonValue(const QJsonValue &root) {
    QMap<QString, QString> result;
    flattenJson(root, "", result);
    return result;
}

使用示例 #

#include <QJsonDocument>
#include <QDebug>

int main() {
    // 解析输入的JSON字符串
    QString jsonStr = R"(
    {
        "date": 1681693886,
        "online": true,
        "none": null,
        "list": {
            "arr": [60,100,100,100,100,100],
            "multiArr": [["hi","my","name"],["is","unknown"],[{"first":0},{"last":100}]],
            "num": 60
        }
    }
    )";
    QJsonDocument doc = QJsonDocument::fromJson(jsonStr.toUtf8());
    QMap<QString, QString> flatMap = flattenQJsonValue(doc.object());

    // 按照示例格式输出
    for (auto it = flatMap.constBegin(); it != flatMap.constEnd(); ++it) {
        qDebug().noquote() << QString("key = \"%1\",%2value = \"%3\"")
                              .arg(it.key())
                              .arg(QString(25 - it.key().length(), ' '))
                              .arg(it.value());
    }
    return 0;
}

说明 #

• 针对double类型，使用科学计数法输出（保留5位小数），和示例格式一致；如果需要其他格式，可修改QString::number的参数。
• 键路径的生成逻辑：根节点为空路径，object的键直接追加，array的索引转为字符串追加，层级用.分隔。
• 所有值统一转为字符串，符合示例中的输出格式。

内容的提问来源于stack exchange，提问作者marc