arduino 之 json 再测试（key是否存在）

1.使用containsKey（）：

String do_back(String json) {
StaticJsonDocument<200> sjdoc;
deserializeJson(sjdoc, json);
String val=sjdoc["hlf"].as<String>();
Serial.print("val:"); Serial.println(val);
Serial.print("sjdoc.containsKey(”hlf“):"); Serial.println(sjdoc.containsKey("hlf"));
Serial.print("sjdoc.containsKey（”hlf_set“）:"); Serial.println(sjdoc.containsKey("hlf_set"));
Serial.print("sjdoc[”hlf_set“].containsKey（”ctl“）:"); Serial.println(sjdoc["hlf_set"].containsKey("ctl"));

if(val=="?"){
Serial.println("val=?:y");

}
return "";
}

串口输出结果：

09:37:08.785 -> Message:{"hlf":"?"}
09:37:08.785 -> -----------------------
09:37:08.785 -> val:?
09:37:08.785 -> sjdoc.containsKey(”hlf“):1
09:37:08.785 -> sjdoc.containsKey（”hlf_set“）:0
09:37:08.785 -> sjdoc[”hlf_set“].containsKey（”ctl“）:0
09:37:08.785 -> val=?:y
 

09:37:26.268 -> Message:{"hlf_set":"?"}
09:37:26.268 -> -----------------------
09:37:26.268 -> val:null
09:37:26.268 -> sjdoc.containsKey(”hlf“):0
09:37:26.268 -> sjdoc.containsKey（”hlf_set“）:1
09:37:26.268 -> sjdoc[”hlf_set“].containsKey（”ctl“）:0
 

09:38:35.055 -> Message:{"hlf_set":{"ctl":"0","max":"25.2"}}
09:38:35.055 -> -----------------------
09:38:35.055 -> val:null
09:38:35.055 -> sjdoc.containsKey(”hlf“):0
09:38:35.055 -> sjdoc.containsKey（”hlf_set“）:1
09:38:35.055 -> sjdoc[”hlf_set“].containsKey（”ctl“）:1

09:39:07.613 -> Message:{"hlf_set":{"ct":"0","max":"25.2"}}
09:39:07.613 -> -----------------------
09:39:07.613 -> val:null
09:39:07.613 -> sjdoc.containsKey(”hlf“):0
09:39:07.613 -> sjdoc.containsKey（”hlf_set“）:1
09:39:07.613 -> sjdoc[”hlf_set“].containsKey（”ctl“）:0

2.利用null值

String do_back(String json) {
  StaticJsonDocument<200> sjdoc;
  deserializeJson(sjdoc, json);
  String val=sjdoc["hlf"].as<String>();
  Serial.print("val:");  Serial.println(val);
const char* hlf_set =  sjdoc[”hlf_set“];
const char* hlf_set_ctl =  sjdoc[”hlf_set“]["ctl"];
const char* hlf_set_max =  sjdoc[”hlf_set“]["max"];

if(hlf_set){
  Serial.print(hlf_set==ture:");  Serial.println(hlf_set);
}else{
  Serial.print(hlf_set==f:");  Serial.println(hlf_set);
}
if(hlf_set_ctl){
  Serial.print(hlf_set_ctl==ture:");  Serial.println(hlf_set_ctl);
}else{
  Serial.print(hlf_se_ctlt==f:");  Serial.println(hlf_set_ctl);
}
if(hlf_set_max){
  Serial.print(hlf_set_max==ture:");  Serial.println(hlf_set_max);
}else{
  Serial.print(hlf_se_max==f:");  Serial.println(hlf_set_max);
}
  if(val=="?"){
      Serial.println("val=?:y");
      
  }
 return "";
}

串口输出结果：

10:09:38.664 -> Message:{"hlf_set":{"ct":"0","max":"25.2"}}
10:09:38.664 -> -----------------------
10:09:38.664 -> val:null
10:09:38.698 -> hlf_set==f:
10:09:38.698 -> hlf_se_ctlt==f:
10:09:38.698 -> hlf_set_max==ture:25.2

10:10:33.065 -> Message:{"hlf_set":{"ctl":"0","min":"25.2"}}
10:10:33.065 -> -----------------------
10:10:33.100 -> val:null
10:10:33.100 -> hlf_set==f:
10:10:33.100 -> hlf_set_ctl==ture:0
10:10:33.100 -> hlf_se_max==f:

10:11:21.062 -> Message:{"hlf_set":"15"}
10:11:21.062 -> -----------------------
10:11:21.062 -> val:null
10:11:21.062 -> hlf_set==ture:15
10:11:21.062 -> hlf_se_ctlt==f:
10:11:21.062 -> hlf_se_max==f:

10:12:24.234 -> Message:{"hlf_set":{"ctl":"0","max":"25.2","min":"15.2"}}
10:12:24.268 -> -----------------------
10:12:24.268 -> val:null
10:12:24.268 -> hlf_set==f:
10:12:24.268 -> hlf_set_ctl==ture:0
10:12:24.268 -> hlf_set_max==ture:25.2