c++ - 添加文本到json C++

Question

有一个JSON文件，我怎样才能在那里添加信息以便留下过去？做了这样的事情，不起作用:

QFile File(pathJSONProject);
File.open(QIODevice::ReadOnly | QIODevice::Text);
QJsonParseError JsonParseError;
QJsonDocument JsonDocument = QJsonDocument::fromJson(File.readAll(), &JsonParseError);

QJsonObject json = JsonDocument.object();

json.insert("Расстояние", dlgOpen->distance);
json.insert("Размер", dlgOpen->size);
json.insert("Путь", pathFolder);
QJsonDocument document(json);
File.open(QFile::WriteOnly | QFile::Text | QFile::Truncate);
File.write(document.toJson());
File.close();

我想向文件中添加条目。做不到。它不会改变。

首先，文件是这样的吗？他必须如何添加新条目？

{
    "Name": "45",
    "Path": "C:/Users/Dmitry/Desktop/45.json"
}

如何向数组添加新条目？

Answer 1

始终处理QFile::open() 的返回值以检查它是否成功。

---

可以有多种方式在 JSON 中插入数组。这是一个例子:

#include <QDebug>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>

int main()
{
    const auto data = R"({ "Name": "45", "Path": "C:\file.json" })";

    auto doc = QJsonDocument::fromJson( data );
    qDebug() << "BEFORE:\n\n"
             << qPrintable( doc.toJson( QJsonDocument::Indented ) );

    // Create an array and add objects
    const auto obj1 = QJsonObject{ { "name", "abc" }, { "default", 11 } };
    const auto obj2 = QJsonObject{ { "name", "xyz" }, { "default", 22 } };

    auto obj = doc.object();
    obj.insert( "array", QJsonArray{ obj1, obj2 } );

    doc.setObject( obj );
    qDebug() << "\nAFTER:\n"
             << qPrintable( doc.toJson( QJsonDocument::Indented ) );

    // Add more objects to array

    const auto obj3 = QJsonObject
    {
        { "name", "def" },
        { "default", 33 },
        { "new1", "1" },
        { "new2", "2" }     // Add any number of objects...
    };

    const auto obj4 = QJsonObject{ { "name", "jkl" }, { "default", 44 } };

    // Get existing array to append more elements
    auto arr = doc.object()[ "array" ].toArray();
    arr.append( obj3 );
    arr.append( obj4 );

    // Set old array to newly updated one
    obj[ "array" ] = arr;

    doc.setObject( obj );
    qDebug() << "\nAFTER THAT:\n"
             << qPrintable( doc.toJson( QJsonDocument::Indented ) );

    return 0;
}

输出:

BEFORE:

 {
    "Name": "45",
    "Path": "C:\file.json"
}


AFTER:
 {
    "Name": "45",
    "Path": "C:\file.json",
    "array": [
        {
            "default": 11,
            "name": "abc"
        },
        {
            "default": 22,
            "name": "xyz"
        }
    ]
}


AFTER THAT:
 {
    "Name": "45",
    "Path": "C:\file.json",
    "array": [
        {
            "default": 11,
            "name": "abc"
        },
        {
            "default": 22,
            "name": "xyz"
        },
        {
            "default": 33,
            "name": "def",
            "new1": "1",
            "new2": "2"
        },
        {
            "default": 44,
            "name": "jkl"
        }
    ]
}

---

另外，看看 QJsonArray::fromStringList()和 QJsonArray::fromVariantList() .