json文件解析

对json文本的解析有两种方法：

第一种：利用 child指针进行访问

• 利用child指针进行访问，需要不断的进行child，以进入深层循环中。
• 访问面文本的slots数组中的成员

• {
      "semantic":{
          "slots":[
              {
                  "name":"ZhangSan",
                  "ip":"ZhangSan"
              },
              {
                  "name":"LiSi",
                  "ip":"ZhangSan"
              },
              {
                  "name":"WangWu",
                  "ip":"ZhangSan"
              }
          ]
      },
      "rc":0,
      "operation":"CALL",
      "service":"telephone",
      "text":"Call ZhangSan"
  }

  解析方法：

• char * jsonStr = "{"semantic":{"slots":[{"name":"ZhangSan","ip":"ZhangSan"},{"name":"LiSi","ip":"ZhangSan"},{"name":"WangWu","ip":"ZhangSan"}]}, "rc":0, "operation":"CALL", "service":"telephone", "text":"Call ZhangSan"}";
      cJSON * root = NULL;
      cJSON * item = NULL;//cjson对象
  
      root = cJSON_Parse(jsonStr);     //解析JSON数据包，并按照cJSON结构体的结构序列化整个数据包。使用该函数会通过malloc()函数在内存中开辟一个空间，使用完成需要手动释放。
      if (!root) 
      {
          printf("Error before: [%s]
  ",cJSON_GetErrorPtr());
      }
      else
      {
          cJSON *slots_arr = cJSON_GetObjectItem(root->child, "slots");
          if( NULL != slots_arr ){
              cJSON *next ;
              int i;
              for(next= slots_arr->child; NULL!=next;)
              {
                  char * ip   = cJSON_GetObjectItem( next , "name")->valuestring ;
                  char * mask = cJSON_GetObjectItem( next , "ip")->valuestring ;
                  printf("ip: %s  mask: %s
  ",ip,mask);    
                  next = next->next    ;
  
              }
          }
      }

  运行输出：

• ip: ZhangSan  mask: ZhangSan
  ip: LiSi  mask: ZhangSan
  ip: WangWu  mask: ZhangSan

第二种：定义cJSON结构体指针进行访问

• 利用cJSON结构体指针访问，一层一个指针，下一层的cJSON指针等于对上一层的cJSON结构体进行访问，从而获得其成员；
• 对下面的json文件进行访问

• {
      "port":[{
          "com3":{
              "bound": 2400,
              "device_type":    "master",
              "device_addr":    ["404887000027", "404887000028"]
              }
          },{
          "com4":{
              "bound": 2400,
              "device_type":    "master",
              "ammeter_addr":    []
              }
          },{
          "com5":{
              "bound": 2400,
              "device_type":    "master",
              "ammeter_addr":    ["404887000027"]
              }
          },{
          "com6":{
              "bound": 2400,
              "device_type":    "master",
              "device_addr":    ["404887000027", "404887000028","404887000027", "404887000028"]
              }
          }
      ]
  }

• 从上面文件可以看出，一共有四层嵌套，分别是：port、com、bound、addr数组；
• 解析方法:

• int port_count, addr_count;
      int i,j;
      char *str;
      cJSON *js_root, *js_one, *js_two, *js_three, *js_four, *it, *member;
  
      str = (char *)malloc(4);
      js_root = load_json_file("device.json");
      
      if(!js_root){
          return -1;
      }
  
      js_one = cJSON_GetObjectItem(js_root, "port");
      if(!js_one){
          printf("no port
  ");
          return -1;
      }
      
      port_count = cJSON_GetArraySize(js_one);   //获取数组中成员个数
      printf("
  port count = %d
  ", port_count);
  
      for(i = 0; i < port_count; i++) {
          js_two = cJSON_GetArrayItem(js_one, i);
          printf("
  ----------------------------------------cJSON_GetArrayItem js_one, %d ----------------------------------------
  ", i);
          printf("%s", cJSON_Print(js_two));
  
          switch(i){
              case 0: strcpy(str, "com3");break;
              case 1: strcpy(str, "com4");break;
              case 2: strcpy(str, "com5");break;
              case 3: strcpy(str, "com6");break;
          }
          js_three = cJSON_GetObjectItem(js_two, str);
          printf("%s
  ", cJSON_Print(js_three));
  
          it = cJSON_GetObjectItem(js_three, "bound");
          printf("name type is %s
  ",it->string);
          printf("name is %d
  ",it->valueint);
  
          it = cJSON_GetObjectItem(js_three, "device_type");
          printf("name type is %s
  ",it->string);
          printf("name is %s
  ",it->valuestring);
  
          js_four = cJSON_GetObjectItem(js_three, "device_addr");
          printf("%s
  ", cJSON_Print(js_four));
          addr_count = cJSON_GetArraySize(js_four);
          printf("%d
  ", addr_count);
  
          if(addr_count == 0)
              continue;
          else{
  
              for(j = 0; j < addr_count; j++) {
                  member = cJSON_GetArrayItem(js_four, j);
                  printf("name is %s
  ",member->valuestring);
              }       
          }    
      }

• 运行结果：

• port count = 4
  
  ----------------------------------------cJSON_GetArrayItem js_one, 0 ----------------------------------------
  {
      "com3":    {
          "bound":    2400,
          "device_type":    "master",
          "device_addr":    ["404887000027", "404887000028"]
      }
  }{
      "bound":    2400,
      "device_type":    "master",
      "device_addr":    ["404887000027", "404887000028"]
  }
  name type is bound
  name is 2400
  name type is device_type
  name is master
  ["404887000027", "404887000028"]
  2
  name is 404887000027
  name is 404887000028
  
  ----------------------------------------cJSON_GetArrayItem js_one, 1 ----------------------------------------
  {
      "com4":    {
          "bound":    2400,
          "device_type":    "master",
          "device_addr":    []
      }
  }{
      "bound":    2400,
      "device_type":    "master",
      "device_addr":    []
  }
  name type is bound
  name is 2400
  name type is device_type
  name is DLT645_2007
  []
  0
  
  ----------------------------------------cJSON_GetArrayItem js_one, 2 ----------------------------------------
  {
      "com5":    {
          "bound":    2400,
          "device_type":    "master",
          "device_addr":    ["404887000027"]
      }
  }{
      "bound":    2400,
      "device_type":    "master",
      "device_addr":    ["404887000027"]
  }
  name type is bound
  name is 2400
  name type is device_type
  name is master
  ["404887000027"]
  1
  name is 404887000027
  
  ----------------------------------------cJSON_GetArrayItem js_one, 3 ----------------------------------------
  {
      "com6":    {
          "bound":    2400,
          "device_type":    "master",
          "device_addr":    ["404887000027", "404887000028", "404887000027", "404887000028"]
      }
  }{
      "bound":    2400,
      "device_type":    "master",
      "device_addr":    ["404887000027", "404887000028", "404887000027", "404887000028"]
  }
  name type is bound
  name is 2400
  name type is device_type
  name is master
  ["404887000027", "404887000028", "404887000027", "404887000028"]
  4
  name is 404887000027
  name is 404887000028
  name is 404887000027
  name is 404887000028