使用json-c库解析一个json数组

【问题标题】：Using the json-c library to parse a json array使用json-c库解析一个json数组
【发布时间】：2021-01-27 07:21:23
【问题描述】：

我有以下 JSON 数据从服务器返回给我，但我无法弄清楚如何为叙述解析机动数组：

{
"maneuvers": [
          {
            "signs": [],
            "index": 0,
            "maneuverNotes": [],
            "direction": 8,
            "narrative": "Start out going east on Clarendon Blvd toward N Queen St.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/icon-dirs-start_sm.gif",
            "distance": 0.031,
            "time": 6,
            "linkIds": [],
            "streets": [
              "Clarendon Blvd"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:00:06",
            "directionName": "East",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-1,38.893164999999996,-77.077957,0,0|purple-2,38.893276,-77.077407,0,0|&center=38.8932205,-77.077682&zoom=15&rand=-1645843521&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.077957,
              "lat": 38.893165
            },
            "turnType": 2
          },
          {
            "signs": [],
            "index": 1,
            "maneuverNotes": [],
            "direction": 4,
            "narrative": "Turn right onto N Queen St.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_right_sm.gif",
            "distance": 0.168,
            "time": 32,
            "linkIds": [],
            "streets": [
              "N Queen St"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:00:32",
            "directionName": "South",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-2,38.893276,-77.077407,0,0|purple-3,38.890857,-77.07708699999999,0,0|&center=38.8920665,-77.077247&zoom=12&rand=-1645843521&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.077407,
              "lat": 38.893276
            },
            "turnType": 2
          },
          {
            "signs": [],
            "index": 2,
            "maneuverNotes": [],
            "direction": 7,
            "narrative": "Turn right onto 14th St N.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_right_sm.gif",
            "distance": 0.003,
            "time": 5,
            "linkIds": [],
            "streets": [
              "14th St N"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:00:05",
            "directionName": "West",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-3,38.890857,-77.07708699999999,0,0|purple-4,38.890842,-77.077148,0,0|&center=38.8908495,-77.07711749999999&zoom=15&rand=-1646228270&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.077087,
              "lat": 38.890857
            },
            "turnType": 2
          },
          {
            "signs": [
              {
                "text": "50",
                "extraText": "",
                "direction": 7,
                "type": 2,
                "url": "http://icons.mqcdn.com/icons/rs2.png?n=50&d=WEST"
              }
            ],
            "index": 3,
            "maneuverNotes": [],
            "direction": 4,
            "narrative": "Merge onto Arlington Blvd/US-50 W via the ramp on the left.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_merge_left_sm.gif",
            "distance": 1.606,
            "time": 151,
            "linkIds": [],
            "streets": [
              "Arlington Blvd",
              "US-50 W"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:02:31",
            "directionName": "South",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-4,38.890842,-77.077148,0,0|purple-5,38.87355,-77.089424,0,0|&center=38.882196,-77.08328599999999&zoom=9&rand=-1646228270&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.077148,
              "lat": 38.890842
            },
            "turnType": 11
          },
          {
            "signs": [],
            "index": 4,
            "maneuverNotes": [],
            "direction": 4,
            "narrative": "Turn left onto N Fillmore St.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_left_sm.gif",
            "distance": 0.408,
            "time": 74,
            "linkIds": [],
            "streets": [
              "N Fillmore St"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:01:14",
            "directionName": "South",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-5,38.87355,-77.089424,0,0|purple-6,38.867782,-77.08811899999999,0,0|&center=38.870666,-77.0887715&zoom=10&rand=-1646228270&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.089424,
              "lat": 38.87355
            },
            "turnType": 6
          },
          {
            "signs": [],
            "index": 5,
            "maneuverNotes": [],
            "direction": 4,
            "narrative": "Stay straight to go onto S Walter Reed Dr.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_straight_sm.gif",
            "distance": 0.884,
            "time": 149,
            "linkIds": [],
            "streets": [
              "S Walter Reed Dr"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:02:29",
            "directionName": "South",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-6,38.867782,-77.08811899999999,0,0|purple-7,38.855185999999996,-77.088584,0,0|&center=38.861484,-77.08835149999999&zoom=9&rand=-1646228270&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.088119,
              "lat": 38.867782
            },
            "turnType": 0
          },
          {
            "signs": [
              {
                "text": "120",
                "extraText": "",
                "direction": 0,
                "type": 545,
                "url": "http://icons.mqcdn.com/icons/rs545.png?n=120"
              }
            ],
            "index": 6,
            "maneuverNotes": [],
            "direction": 5,
            "narrative": "Turn slight left onto S Glebe Rd/VA-120.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/rs_slight_left_sm.gif",
            "distance": 0.593,
            "time": 84,
            "linkIds": [],
            "streets": [
              "S Glebe Rd",
              "VA-120"
            ],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:01:24",
            "directionName": "Southeast",
            "mapUrl": "http://www.mapquestapi.com/staticmap/v4/getmap?key=KEY&type=map&size=225,160&pois=purple-7,38.855185999999996,-77.088584,0,0|purple-8,38.848926,-77.08122999999999,0,0|&center=38.852056,-77.08490699999999&zoom=10&rand=-1646228270&session=55e60cd9-00b6-001a-02b7-20ac-00163e7dd551",
            "startPoint": {
              "lng": -77.088584,
              "lat": 38.855186
            },
            "turnType": 7
          },
          {
            "signs": [],
            "index": 7,
            "maneuverNotes": [],
            "direction": 0,
            "narrative": "2400 S GLEBE RD is on the right.",
            "iconUrl": "http://content.mapquest.com/mqsite/turnsigns/icon-dirs-end_sm.gif",
            "distance": 0,
            "time": 0,
            "linkIds": [],
            "streets": [],
            "attributes": 0,
            "transportMode": "AUTO",
            "formattedTime": "00:00:00",
            "directionName": "",
            "startPoint": {
              "lng": -77.08123,
              "lat": 38.848926
            },
            "turnType": -1
          }
        ]
}

我正在使用json-c 库。我尝试使用循环并获取数组中的索引号，但由于出现错误而无法正确执行。

我将如何访问演习中的叙述部分？

编辑：我得到的错误是当我使用 json_object_array_length(maneuvers) 时，它说机动不是有效的 json 对象。请注意，mauevers 已经是我从父 json-object 解析的数组

【问题讨论】：

    标签： arrays c json json-c


    【解决方案1】：

    如果您向我们展示一些代码以及您遇到的错误，将会很有帮助。

    您应该使用json_object_from_file 读取JSON 文件，然后使用json_object_object_get 获取某个键下的元素。

    真正的基本代码（省略了错误检查以及类型检查 - 例如，我从不检查 maneuvers 是否确实是一个数组）：

    json_object *root = json_object_from_file("path/to/file.json");
json_object *maneuvers = json_object_object_get(root, "maneuvers");
int maneuvers_count = json_object_array_length(maneuvers);
for (int i = 0; i < maneuvers_count; i++)
{
    json_object *element = json_object_array_get_idx(maneuvers, i);
    json_object *narratives = json_object_object_get(element, "narratives");
    char *narratives_str = json_object_get_string(narratives);
}

    有关一些教程，请参阅https://github.com/rbtylee/tutorial-jsonc/blob/master/tutorial/index.md。

    【讨论】：

    • 我正在将 JSON 写入一个字符串，因此我正在从那里读取它。我使用了我在这个post 中找到的方法。我一直在控制台中收到数组不是有效的 JSON 对象的错误
    • 您应该能够使用相同的 json-c API 来解析 JSON。您帖子中的 JSON 看起来有效（例如 cat test.json | jq '.maneuvers[0].narrative' 输出 "Start out going east on Clarendon Blvd toward N Queen St."）。同样，您为这个问题编写的一些代码会有所帮助。
    • 我编写了与您评论完全相同的代码并收到以下错误（在控制台中，以及调试错误）：“断言失败：json_object_get_type(jso) == json_type_array, file C:\vcpkg \builtrees\json-c\src\51ecf1a4a4-799e3998b0.clean\json_object.c，第 1231 行
    • 请发布一个重现问题的最小示例，请参阅stackoverflow.com/help/minimal-reproducible-example
    猜你喜欢
    • 1970-01-01
    • 2014-06-15
    • 1970-01-01
    • 1970-01-01
    • 1970-01-01
    • 1970-01-01
    • 1970-01-01
    • 1970-01-01
    • 2018-08-03
    相关资源
    最近更新 更多
    热门标签
    Java Python linux javascript Mysql C# Docker 算法 前端 SpringBoot Redis Vue spring 设计模式 .net core .net kubernetes c++ 数据库 数据结构 大数据 js 机器学习 微服务 Android Go 程序员 面试 JVM ASP.net core 云原生 人工智能 后端 PHP git CSS golang k8s Nginx Django mybatis 深度学习 多线程 React 架构 devops 爬虫 云计算 Spring Boot LeetCode