前言
上一篇介绍了C语言写的JSON解析库cJSON的使用：使用cJSON库解析和构建JSON字符串
本篇文章介绍，Qt开发环境下QJson库的使用示例。示例代码包含简单和复杂JSON字符串的解析和构建，Qt工程已经开源在Github和Gitee代码托管平台。
- Github仓库地址：
https://github.com/whik/QJson_Demo
- Gitee仓库地址：
https://gitee.com/whik/QJson_Demo
开发平台基于Qt 5.8 Windows。示例的JSON字符串和上一篇使用的是一样的。
JSON解析示例包括：
- 和风天气实时数据
- 心知天气实时数据
- 心知天气3天预报数据
- 城市空气质量AQI信息
- 全国油价信息
- 北京时间等。
由于文章篇幅限制，本篇文章先介绍QJson的解析示例。
QJson解析JSON示例
JSON的解析要对照JSON字符串来理解，关于JSON字符串的介绍，可以参考JSON简介
解析和构建都要先包含如下头文件：
代码语言：javascript复制#include <QJsonDocument>#include <QJsonObject>#include <QJsonArray>示例字符串1：和风天气实时数据
这个JSON字符串中HeWeather6键的值是一个数组，数组内只有1个JSON对象，这个对象里又嵌套了几个JSON对象。
代码语言：javascript复制{ "HeWeather6": [{ "basic": { "cid": "CN101010700", "location": "昌平", "parent_city": "北京", "admin_area": "北京", "cnty": "中国", "lat": "40.21808624", "lon": "116.23590851", "tz": " 8.00" }, "update": { "loc": "2019-07-20 10:21", "utc": "2019-07-20 02:21" }, "status": "ok", "now": { "cloud": "96", "cond_code": "104", "cond_txt": "阴", "fl": "28", "hum": "86", "pcpn": "0.0", "pres": "995", "tmp": "25", "vis": "4", "wind_deg": "100", "wind_dir": "东风", "wind_sc": "1", "wind_spd": "4" } }]}字符串1解析函数
主要是JSON的多层嵌套的解析。
代码语言：javascript复制int Parse_HeWeather_Now_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(he_now_json, &err_rpt);//字符串格式化为JSON
if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc;
QJsonObject root_Obj = root_Doc.object(); QJsonValue weather_Value = root_Obj.value("HeWeather6"); //HeWeather6键的值，是一个数组 if(weather_Value.isArray()) //可省略 { QJsonObject weather_Obj = weather_Value.toArray().at(0).toObject(); //HeWeather6数组就含有一个元素0
/* basic键信息 */ QJsonObject basic_Obj = weather_Obj.value("basic").toObject(); QString cid = basic_Obj.value("cid").toString(); QString location = basic_Obj.value("location").toString(); QString parent_city = basic_Obj.value("parent_city").toString(); QString cnty = basic_Obj.value("cnty").toString(); QString lat = basic_Obj.value("lat").toString(); QString lon = basic_Obj.value("lon").toString(); QString basic_info = cid " " parent_city " " cnty " " lat " " lon; qDebug() << basic_info;
/* update键信息 */ QJsonObject update_Obj = weather_Obj.value("update").toObject(); QString loc = "当地时间:" update_Obj.value("loc").toString(); //当地时间 QString utc = "UTC时间:" update_Obj.value("utc").toString(); //UTC时间 QString status = "解析状态:" weather_Obj.value("status").toString(); //"ok" qDebug() << loc " " utc " " status;
/* now键信息*/ QJsonObject now_Obj = weather_Obj.value("now").toObject(); QString cond_txt = "白天天气:" now_Obj.value("cond_txt").toString(); QString hum = "湿度:" now_Obj.value("hum").toString(); QString tmp = "温度:" now_Obj.value("tmp").toString(); QString wind_dir = "风向:" now_Obj.value("wind_dir").toString(); QString wind_sc = "风级:" now_Obj.value("wind_sc").toString(); qDebug() << cond_txt " " hum " " tmp " " wind_dir " " wind_sc; } qDebug() << "解析完成!"; } return 0;}示例字符串2：心知天气实时数据
这个字符串和上面那个一样，都是数组元素是JSON对象，对象的值又是一个JSON对象。
代码语言：javascript复制{ "results": [{ "location": { "id": "WX4FBXXFKE4F", "name": "北京", "country": "CN", "path": "北京,北京,中国", "timezone": "Asia/Shanghai", "timezone_offset": " 08:00" }, "now": { "text": "晴", "code": "1", "temperature": "-7" }, "last_update": "2018-12-06T22:05:00 08:00" }]}字符串2解析函数
代码语言：javascript复制int Parse_Seniverse_Now_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(seniverse_now_json, &err_rpt);//字符串格式化为JSON if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc; QJsonObject root_Obj = root_Doc.object(); QJsonValue result_Value = root_Obj.value("results"); if(result_Value.isArray()) { QJsonObject result_Obj = result_Value.toArray().at(0).toObject();
QString last_update = result_Obj.value("last_update").toString(); qDebug() << last_update;
/* location键的值 */ QJsonObject location_Obj = result_Obj.value("location").toObject(); QString id = location_Obj.value("id").toString(); QString name = location_Obj.value("name").toString(); QString timezone = location_Obj.value("timezone").toString(); QString path = location_Obj.value("path").toString(); QString loc_str = id " " name " " timezone " " path ; qDebug() << loc_str;
/* now键 */ QJsonObject now_Obj = result_Obj.value("now").toObject(); QString code = "天气代码: " now_Obj.value("code").toString(); QString temperature = "当前温度：" now_Obj.value("temperature").toString(); QString text = "天气：" now_Obj.value("text").toString(); qDebug() << code << temperature << text; } } return 0;}示例字符串3：心知3天天气预报数据
代码语言：javascript复制{ "results": [{ "location": { "id": "WS10730EM8EV", "name": "深圳", "country": "CN", "path": "深圳,深圳,广东,中国", "timezone": "Asia/Shanghai", "timezone_offset": " 08:00" }, "daily": [{ "date": "2018-12-06", "text_day": "阴", "code_day": "9", "text_night": "阴", "code_night": "9", "high": "25", "low": "16", "precip": "", "wind_direction": "无持续风向", "wind_direction_degree": "", "wind_speed": "10", "wind_scale": "2" }, { "date": "2018-12-07", "text_day": "阴", "code_day": "9", "text_night": "小雨", "code_night": "13", "high": "20", "low": "15", "precip": "", "wind_direction": "北", "wind_direction_degree": "0", "wind_speed": "15", "wind_scale": "3" }, { "date": "2018-12-08", "text_day": "小雨", "code_day": "13", "text_night": "小雨", "code_night": "13", "high": "17", "low": "12", "precip": "", "wind_direction": "东北", "wind_direction_degree": "45", "wind_speed": "15", "wind_scale": "3" }], "last_update": "2018-12-06T18:00:00 08:00" }]}字符串3解析函数
代码语言：javascript复制int Parse_Seniverse_Forecast_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(seniverse_forcast_json, &err_rpt);//字符串格式化为JSON if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc; QJsonObject root_Obj = root_Doc.object(); QJsonValue result_Value = root_Obj.value("results"); if(result_Value.isArray()) { QJsonObject result_Obj = result_Value.toArray().at(0).toObject();
QString last_update = result_Obj.value("last_update").toString(); qDebug() << last_update; /* location键的值 */ QJsonObject location_Obj = result_Obj.value("location").toObject(); QString id = location_Obj.value("id").toString(); QString name = location_Obj.value("name").toString(); QString timezone = location_Obj.value("timezone").toString(); QString path = location_Obj.value("path").toString(); QString loc_str = id " " name " " timezone " " path ; qDebug() << loc_str;
/* daily预报天气3天，数组元素3个*/ QJsonValue daily_Vaule = result_Obj.value("daily"); if(daily_Vaule.isArray()) { for(int idx = 0; idx <= 2; idx ) { QJsonObject daily_Obj = daily_Vaule.toArray().at(idx).toObject(); QString date = " 日期：" daily_Obj.value("date").toString(); QString text_day =" 白天天气：" daily_Obj.value("text_day").toString(); QString high = " 最高温度：" daily_Obj.value("high").toString(); QString low = " 最低温度：" daily_Obj.value("low").toString(); QString wind_direction = " 风向：" daily_Obj.value("wind_direction").toString(); QString wind_scale = " 风级：" daily_Obj.value("wind_scale").toString(); qDebug() << date text_day high low wind_direction wind_scale; } } } } return 0;}示例字符串4：空气AQI质量指数
包含10个元素的数组。
代码语言：javascript复制{ "status": "0", "citye": "changchun", "city": "长春", "citycode": "101060101", "aqi": "50", "data": [{ "add": "长春", "aqi": "50", "pm25": "22", "per": "优", "lv": "1" }, { "add": "食品厂", "aqi": "54", "pm25": "18", "per": "良", "lv": "2" }, { "add": "客车厂", "aqi": "52", "pm25": "20", "per": "良", "lv": "2" }, { "add": "邮电学院", "aqi": "35", "pm25": "24", "per": "优", "lv": "1" }, { "add": "劳动公园", "aqi": "45", "pm25": "19", "per": "优", "lv": "1" }, { "add": "园林处", "aqi": "45", "pm25": "21", "per": "优", "lv": "1" }, { "add": "净月潭", "aqi": "46", "pm25": "30", "per": "优", "lv": "1" }, { "add": "甩湾子", "aqi": "51", "pm25": "24", "per": "良", "lv": "2" }, { "add": "经开区环卫处", "aqi": "48", "pm25": "25", "per": "优", "lv": "1" }, { "add": "高新区管委会", "aqi": "51", "pm25": "16", "per": "良", "lv": "2" }, { "add": "岱山公园", "aqi": "49", "pm25": "19", "per": "优", "lv": "1" }]}字符串4解析函数
代码语言：javascript复制int Parse_AQI_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(AQI_json, &err_rpt);//字符串格式化为JSON if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc; QJsonObject root_Obj = root_Doc.object();
QString city = root_Obj.value("city").toString(); QString citycode = root_Obj.value("citycode").toString(); QString citye = root_Obj.value("citye").toString(); QString status = root_Obj.value("status").toString(); qDebug() << city " " citycode " " citye " " status;
/* data键 */ QJsonValue data_Vaule = root_Obj.value("data"); if(data_Vaule.isArray()) { for(int idx = 0; idx <= 10; idx ) { QJsonObject data_Obj = data_Vaule.toArray().at(idx).toObject(); QString add = "地址：" data_Obj.value("add").toString(); QString aqi = " AQI：" data_Obj.value("aqi").toString(); QString lv = " 空气质量等级：" data_Obj.value("lv").toString(); QString per = " 空气质量：" data_Obj.value("per").toString(); QString pm25 = " PM2.5等级：" data_Obj.value("pm25").toString(); qDebug() << add aqi lv per pm25; } } } return 0;}示例字符串5：北京标准时间
比较简单一个JSON对象
代码语言：javascript复制{ "success": "1", "result": { "timestamp": "1542456793", "datetime_1": "2018-11-17 20:13:13", "datetime_2": "2018年11月17日 20时13分13秒", "week_1": "6", "week_2": "星期六", "week_3": "周六", "week_4": "Saturday" }}字符串5解析函数
代码语言：javascript复制int Parse_BJTime_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(bj_time_json, &err_rpt);//字符串格式化为JSON if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc; QJsonObject root_Obj = root_Doc.object();
QString success = root_Obj.value("success").toString(); /* result键 */ QJsonObject result_Obj = root_Obj.value("result").toObject(); QString datetime_1 = result_Obj.value("datetime_1").toString(); QString datetime_2 = result_Obj.value("datetime_2").toString(); QString timestamp = result_Obj.value("timestamp").toString(); QString week_1 = result_Obj.value("week_1").toString(); QString week_2 = result_Obj.value("week_2").toString(); QString week_3 = result_Obj.value("week_3").toString(); QString week_4 = result_Obj.value("week_4").toString(); qDebug() << datetime_1 << datetime_2; qDebug() << week_1 << week_2 << week_3 << week_4; } return 0;}示例字符串6：全国城市油价信息
这种格式的字符串也是标准的JSON字符串，[]表示数组，这个数组内包含了5个字符串：
代码语言：javascript复制["北京", "6.78", "7.21", "8.19", "6.45"]但是这种不是，{}表示对象：
代码语言：javascript复制{"北京", "6.78", "7.21", "8.19", "6.45"}一个数组内包含5个元素，每个元素又是一个数组，每个数组又包含5个字符串，属于数组的嵌套：
代码语言：javascript复制{ "status": "0", "msg": "全国各省份汽柴油价格信息", "update": "2019-07-21", "data": [ ["地区", "92号", "95号", "98号", "0号柴油"], ["北京", "6.78", "7.21", "8.19", "6.45"], ["上海", "6.74", "7.17", "7.87", "6.39"], ["江苏", "6.75", "7.18", "8.06", "6.37"], ["天津", "6.77", "7.15", "8.07", "6.41"] ], "About": "wcc", "Home": "www.wangchaochao.top"}字符串6解析函数
代码语言：javascript复制//解析数组嵌套的JSON字符串int Parse_Oil_Price_Json(void){ QJsonParseError err_rpt; QJsonDocument root_Doc = QJsonDocument::fromJson(oil_price_json, &err_rpt);//字符串格式化为JSON if(err_rpt.error != QJsonParseError::NoError) { qDebug() << "JSON格式错误"; return -1; } else //JSON格式正确 { // qDebug() << "JSON格式正确：n" << root_Doc; QJsonObject root_Obj = root_Doc.object();
QString msg = root_Obj.value("msg").toString(); QString update = root_Obj.value("update").toString(); QString status = root_Obj.value("status").toString(); QString About = root_Obj.value("About").toString(); QString Home = root_Obj.value("Home").toString(); qDebug() << msg << update << status << About << Home;
/* data键解析 */ QJsonValue data_Value = root_Obj.value("data"); if(data_Value.isArray()) //数组中包含5个数组，每个数组5个字符串元素 { for(int idx = 0; idx <= 4; idx ) { QJsonValue price_Obj = data_Value.toArray().at(idx); if(price_Obj.isArray()) { QString str1 = price_Obj.toArray().at(0).toString();// 每个元素是一个字符串 QString str2 = price_Obj.toArray().at(1).toString(); QString str3 = price_Obj.toArray().at(2).toString(); QString str4 = price_Obj.toArray().at(3).toString(); QString str5 = price_Obj.toArray().at(4).toString(); qDebug() << str1 << str2 << str3 << str4 << str5 ; } } } } return 0;}参考资料
- JSON官方网站：
http://www.json.org/json-zh.html
总结
JSON解析配合API接口，就可以实现一些有趣的工具了，如全国油价查询工具，全国天气查询，空气质量查询，黄历查询，生活指数等等实用工具的开发。
分享几个免费的API提供平台：
- K780：
http://www.k780.com/api
- 天气API：
http://api.help.bj.cn/api/
- 心知天气：
https://www.seniverse.com/
- 和风天气：
http://www.heweather.com
- 聚合数据：
https://www.juhe.cn/
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