C/C++ Qt 运用JSON决议库 [基础篇]-编程知识-白鹭情

JSON是一种简单的轻量级资料交换格式，Qt库为JSON的相关操作提供了完整的类支持，使用JSON决议档案之前需要先通过TextStream流将档案读入到字符串变量内，然后再通过QJsonDocument等库对该JSON格式进行决议，以提取出我们所需栏位，

首先创建一个决议档案,命名为config.json我们将通过代码依次决议这个JSON档案中的每一个自变量,具体决议代码如下:

{
    "blog": "https://www.cnblogs.com/lyshark",
    "enable": true,
    "status": 1024,
    
    "GetDict": {"address":"192.168.1.1","username":"root","password":"123456","update":"2020-09-26"},
    "GetList": [1,2,3,4,5,6,7,8,9,0],
    
    "ObjectInArrayJson":
    {
        "One": ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"],
        "Two": ["Sunday","Monday","Tuesday"]
    },
    
    "ArrayJson": [
        ["192.168.1.1","root","22"],
        ["192.168.1.2","root","23"],
        ["192.168.1.3","root","24"],
        ["192.168.1.4","root","25"],
        ["192.168.1.5","root","26"]
    ],
    
    "ObjectJson": [
        {"address":"192.168.1.1","username":"admin"},
        {"address":"192.168.1.2","username":"root"},
        {"address":"192.168.1.3","username":"lyshark"}
    ]
}

首先实作读写文本档案,通过QT中封装的<QFile>库可实作对文本档案的读取操作,读取JSON档案可使用该方式.

#include <QCoreApplication>
#include <iostream>
#include <QString>
#include <QTextStream>
#include <QFile>
#include <QDir>
#include <QFileInfo>

#include <QJsonDocument>
#include <QJsonParseError>
#include <QJsonObject>
#include <QJsonArray>
#include <QJsonValue>
#include <QJsonValueRef>

// 传入文本路径,读取并输出
int readonly_string_file(QString file_path)
{
    QFile this_file_ptr(file_path);

    // 判断档案是否存在
    if(false == this_file_ptr.exists())
    {
        std::cout << "档案不存在" << std::endl;
        return 0;
    }

    /*
     * 档案打开属性包括如下
     * QIODevice::ReadOnly  只读方式打开
     * QIODevice::WriteOnly 写入方式打开
     * QIODevice::ReadWrite 读写方式打开
     * QIODevice::Append    追加方式打开
     * QIODevice::Truncate  截取方式打开
     * QIODevice::Text      文本方式打开
     */

    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        std::cout << "打开失败" << std::endl;
        return 0;
    }

    // 读取到文本中的字符串
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();

    std::cout <<"读入长度: " << this_file_ptr.size() << std::endl;
    std::cout << "字符串: " << string_value.toStdString() << std::endl;
    this_file_ptr.close();
}

// 逐行读取文本档案
// PowerBy: www.cnblogs.com/lyshark
void read_line_file()
{
    QFile this_file_ptr("d:/config.json");

    if(this_file_ptr.open((QIODevice::ReadOnly | QIODevice::Text)))
    {
        QByteArray byte_array;

        while(false == this_file_ptr.atEnd())
        {
            byte_array += this_file_ptr.readLine();
        }

        std::cout << "完整文本: " << QString(byte_array).toStdString() << std::endl;
        this_file_ptr.close();
    }
}

// 传入文本路径与写入内容,写入到档案
void write_string_file(QString file_path, QString string_value)
{
    QFile this_file_ptr(file_path);

    // 判断档案是否存在
    if(false == this_file_ptr.exists())
    {
        return;
    }

    // 打开失败
    if(false == this_file_ptr.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        return;
    }

    //写入内容，注意需要转码，否则会报错
    QByteArray write_string = string_value.toUtf8();

    //写入QByteArray格式字符串
    this_file_ptr.write(write_string);
    this_file_ptr.close();
}

// 计算档案或目录大小
// PowerBy: www.cnblogs.com/lyshark
unsigned int GetFileSize(QString path)
{
    QFileInfo info(path);
    unsigned int ret = 0;
    if(info.isFile())
    {
        ret = info.size();
    }
    else if(info.isDir())
    {
        QDir dir(path);
        QFileInfoList list = dir.entryInfoList();
        for(int i = 0; i < list.count(); i++)
        {
            if((list[i].fileName() != ".") && (list[i].fileName() != ".."))
            {
                ret += GetFileSize(list[i].absoluteFilePath());
            }
        }
    }
    return ret;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    readonly_string_file("d:/config.json");

    // 计算档案或目录大小
    unsigned int file_size = GetFileSize("d:/xunjian");
    std::cout << "获取档案或目录大小: " << file_size << std::endl;

    // 覆写写入档案
    QString write_file_path = "d:/test.json";
    QString write_string = "hello lyshark";
    write_string_file(write_file_path,write_string);

    return a.exec();
}

实作决议根物件中的单一的键值对,例如决议组态档中的blog,enable,status等这些独立的栏位值.

// 读取JSON文本
// PowerBy: www.cnblogs.com/lyshark
QString readonly_string(QString file_path)
{
    QFile this_file_ptr(file_path);
    if(false == this_file_ptr.exists())
    {
        return "None";
    }
    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        return "None";
    }
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();
    this_file_ptr.close();
    return string_value;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    QString config = readonly_string("d:/config.json");
    if(config == "None")
    {
        return 0;
    }

    // 字符串格式化为JSON
    QJsonParseError err_rpt;
    QJsonDocument  root_document = QJsonDocument::fromJson(config.toUtf8(), &err_rpt);
    if(err_rpt.error != QJsonParseError::NoError)
    {
        std::cout << "JSON格式错误" << std::endl;
        return 0;
    }

    // 获取到Json字符串的根节点
    QJsonObject root_object = root_document.object();

    // 决议blog栏位
    QString blog = root_object.find("blog").value().toString();
    std::cout << "栏位对应的值 = > "<< blog.toStdString() << std::endl;

    // 决议enable栏位
    bool enable = root_object.find("enable").value().toBool();
    std::cout << "是否开启状态: " << enable << std::endl;

    // 决议status栏位
    int status = root_object.find("status").value().toInt();
    std::cout << "状态数值: " << status << std::endl;

    return a.exec();
}

实作决议简单的单物件与单阵列结构,如上组态档中的GetDict与GetList既是我们需要决议的内容.

// 读取JSON文本
QString readonly_string(QString file_path)
{
    QFile this_file_ptr(file_path);
    if(false == this_file_ptr.exists())
    {
        return "None";
    }
    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        return "None";
    }
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();
    this_file_ptr.close();
    return string_value;
}
// PowerBy: www.cnblogs.com/lyshark
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    QString config = readonly_string("d:/config.json");
    if(config == "None")
    {
        return 0;
    }

    // 字符串格式化为JSON
    QJsonParseError err_rpt;
    QJsonDocument  root_document = QJsonDocument::fromJson(config.toUtf8(), &err_rpt);
    if(err_rpt.error != QJsonParseError::NoError)
    {
        std::cout << "JSON格式错误" << std::endl;
        return 0;
    }

    // 获取到Json字符串的根节点
    QJsonObject root_object = root_document.object();

    // 决议单一物件
    // PowerBy: www.cnblogs.com/lyshark
    QJsonObject get_dict_ptr = root_object.find("GetDict").value().toObject();
    QVariantMap map = get_dict_ptr.toVariantMap();

    if(map.contains("address") && map.contains("username") && map.contains("password") && map.contains("update"))
    {
        QString address = map["address"].toString();
        QString username = map["username"].toString();
        QString password = map["password"].toString();
        QString update = map["update"].toString();

        std::cout
                  << " 地址: " << address.toStdString()
                  << " 用户名: " << username.toStdString()
                  << " 密码: " << password.toStdString()
                  << " 更新日期: " << update.toStdString()
                  << std::endl;
    }

    // 决议单一阵列
    QJsonArray get_list_ptr = root_object.find("GetList").value().toArray();

    for(int index=0; index < get_list_ptr.count(); index++)
    {
        int ref_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/get_list_ptr.at(index).toInt();
        std::cout <<"输出阵列元素: " << ref_value << std::endl;
    }

    return a.exec();
}

实作决议物件嵌套物件且物件中嵌套阵列结构,如上组态档中的ObjectInArrayJson既是我们需要决议的内容.

// 读取JSON文本
QString readonly_string(QString file_path)
{
    QFile this_file_ptr(file_path);
    if(false == this_file_ptr.exists())
    {
        return "None";
    }
    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        return "None";
    }
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();
    this_file_ptr.close();
    return string_value;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    QString config = readonly_string("d:/config.json");
    if(config == "None")
    {
        return 0;
    }

    // 字符串格式化为JSON
    // PowerBy: www.cnblogs.com/lyshark
    QJsonParseError err_rpt;
    QJsonDocument  root_document = QJsonDocument::fromJson(config.toUtf8(), &err_rpt);
    if(err_rpt.error != QJsonParseError::NoError)
    {
        std::cout << "JSON格式错误" << std::endl;
        return 0;
    }

    // 获取到Json字符串的根节点
    QJsonObject root_object = root_document.object();

    // 找到Object物件
    QJsonObject one_object_json = root_object.find("ObjectInArrayJson").value().toObject();

    // 转为MAP映射
    QVariantMap map = one_object_json.toVariantMap();

    // 寻找One键
    QJsonArray array_one = map["One"].toJsonArray();

    for(int index=0; index < array_one.count(); index++)
    {
        QString value = https://www.cnblogs.com/LyShark/archive/2022/01/06/array_one.at(index).toString();

        std::cout <<"One => "<< value.toStdString() << std::endl;
    }

    // 寻找Two键
    QJsonArray array_two = map["Two"].toJsonArray();

    for(int index=0; index < array_two.count(); index++)
    {
        QString value = https://www.cnblogs.com/LyShark/archive/2022/01/06/array_two.at(index).toString();

        std::cout <<"Two => "<< value.toStdString() << std::endl;
    }

    return a.exec();
}

实作决议阵列中的阵列结构,如上组态档中的ArrayJson既是我们需要决议的内容.

// 读取JSON文本
// PowerBy: www.cnblogs.com/lyshark
QString readonly_string(QString file_path)
{
    QFile this_file_ptr(file_path);
    if(false == this_file_ptr.exists())
    {
        return "None";
    }
    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        return "None";
    }
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();
    this_file_ptr.close();
    return string_value;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    QString config = readonly_string("d:/config.json");
    if(config == "None")
    {
        return 0;
    }

    // 字符串格式化为JSON
    QJsonParseError err_rpt;
    QJsonDocument  root_document = QJsonDocument::fromJson(config.toUtf8(), &err_rpt);
    if(err_rpt.error != QJsonParseError::NoError)
    {
        std::cout << "json 格式错误" << std::endl;
        return 0;
    }

    // 获取到Json字符串的根节点
    QJsonObject root_object = root_document.object();

    // 获取MyJson阵列
    QJsonValue array_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/root_object.value("ArrayJson");

    // 验证节点是否为阵列
    if(array_value.isArray())
    {
        // 得到阵列个数
        int array_count = array_value.toArray().count();

        // 回圈阵列个数
        for(int index=0;index <= array_count;index++)
        {
            QJsonValue parset = array_value.toArray().at((index));
            if(parset.isArray())
            {
                QString address = parset.toArray().at(0).toString();
                QString username = parset.toArray().at(1).toString();
                QString userport = parset.toArray().at(2).toString();

                std::cout
                        << "地址: " << address.toStdString()
                        << " 用户名: " << username.toStdString()
                        << " 埠号: " << userport.toStdString()
                << std::endl;
            }
        }
    }

    return a.exec();
}

实作决议阵列中的多物件结构,如上组态档中的ObjectJson既是我们需要决议的内容.

// 读取JSON文本
// PowerBy: www.cnblogs.com/lyshark
QString readonly_string(QString file_path)
{
    QFile this_file_ptr(file_path);
    if(false == this_file_ptr.exists())
    {
        return "None";
    }
    if(false == this_file_ptr.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        return "None";
    }
    QString string_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/this_file_ptr.readAll();
    this_file_ptr.close();
    return string_value;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 读取档案
    QString config = readonly_string("d:/config.json");
    if(config == "None")
    {
        return 0;
    }

    // 字符串格式化为JSON
    QJsonParseError err_rpt;
    QJsonDocument  root_document = QJsonDocument::fromJson(config.toUtf8(), &err_rpt);
    if(err_rpt.error != QJsonParseError::NoError)
    {
        std::cout << "json 格式错误" << std::endl;
        return 0;
    }

    // 获取到Json字符串的根节点
    QJsonObject root_object = root_document.object();

    // 获取MyJson阵列
    QJsonValue object_value = https://www.cnblogs.com/LyShark/archive/2022/01/06/root_object.value("ObjectJson");

    // 验证是否为阵列
    // PowerBy: www.cnblogs.com/lyshark
    if(object_value.isArray())
    {
        // 获取物件个数
        int object_count = object_value.toArray().count();

        // 回圈个数
        for(int index=0;index <= object_count;index++)
        {
            QJsonObject obj = object_value.toArray().at(index).toObject();

            // 验证阵列不为空
            if(!obj.isEmpty())
            {
                QString address = obj.value("address").toString();
                QString username = obj.value("username").toString();

                std::cout << "地址: " << address.toStdString() << " 用户: " << username.toStdString() << std::endl;
            }
        }
    }

    return a.exec();
}

文章出处：https://www.cnblogs.com/LyShark/p/15769760.html
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