I need some help to extract a string from a string

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1

Im tearing my hair over this code and hope you can shine some light on it :slight_smile:
I have a String containing some http code; payload. Now I want to extract some specific data in that string but no matter how I try I cant wrap my head around the functions of String.
The data I want to extract is the temperature found in this specific code:
<span id="tempC1">24.75</span>
Now this is what I have made so far but Its problematic.

  String payload = "{}";  //String that contain HTLM
  String searchThis = "tempC1"; // what to search for to find the data
  String cutout = ""; //string that I want to contain the temperature

  if (httpResponseCode>0) {
    Serial.print("HTTP Response code: ");
    Serial.println(httpResponseCode);

    payload = http.getString();    
    cutout = payload.substring(payload.indexOf(searchThis), payload.indexOf(searchThis)+5);payload.indexOf(payload));
      
    Serial.println(cutout);
  }

I really hope you want to help me :slight_smile:

2

Start from less difficult example.
Remove all HTML related parts from the code, work with Strins only:

String payload = "<span id=\"tempC1\">24.75</span>"; 
String searchThis = "tempC1"; // what to search for to find the data
String cutout; //string that I want to contain the temperature

cutout = payload.substring(payload.indexOf(searchThis),payload.indexOf(searchThis)+5);

payload.indexOf(payload);     // <<<< what is purpose of this string?

Serial.println(cutout);

Run this code and show< what you see in the Serial

By the way - what is purpose of the last line of the code before Serial.print statement?

3

The last line was some code I forgot to remove :slight_smile:

Thanks for fast answer, here is the printout of the code above:

we are connected

HTTP Response code: 200

tempC

here comes the data:

tempC

4

This printout is not consistent neither with your code, nor with mine.

5

Sorry, I tried to simplify the code for the post.

String httpGETRequest(const char* serverName) {
  WiFiClient client;
  HTTPClient http;
    
  // Your IP address with path or Domain name with URL path 
  http.begin(client, serverName);
 
  // If you need Node-RED/server authentication, insert user and password below
  //http.setAuthorization("REPLACE_WITH_SERVER_USERNAME", "REPLACE_WITH_SERVER_PASSWORD");
  
  // Send HTTP POST request
  int httpResponseCode = http.GET();
  
  String payload = "{}";  //String that contain HTLM
  String searchThis = "tempC1"; // what to search for to find the data
  String cutout = ""; //string that I want to contain the temperature
  String index = "";

  if (httpResponseCode>0) {
    Serial.print("HTTP Response code: ");
    Serial.println(httpResponseCode);

    //payload = http.getString();    
    String payload = "<span id=\"tempC1\">24.75</span>"; 
    cutout = payload.substring(payload.indexOf(searchThis),payload.indexOf(searchThis)+5);
    index = payload.indexOf(searchThis);
    Serial.println(cutout);
    Serial.println(payload);
    Serial.println(index);
   }
  else {
    Serial.print("Error code: ");
    Serial.println(httpResponseCode);
  }
  // Free resources
  http.end();
  return cutout;
}
6

And what is problem with it?
It seems to be a correct output of your code.

To output the temperature value instead of field name you need to add an offset to the substring() parameters to shift the substring window to the part of the responce where the value is situated

7

Thanks for your patience :slight_smile:
This is the current output:

we are connected
HTTP Response code: 200
tempC
<span id="tempC1">24.75</span>
10
here comes the data:
tempC

I want to know how to extract the "24.75" into another string.

8

please read the last paragraph of the post #6

9

Yes I read that, but how do I do that please?

edit
I figured it out!

cutout = payload.substring(payload.indexOf(searchThis)+8, payload.indexOf(searchThis)+13);
10

good shot :slight_smile: