Seeking advice to create a string?

Projects General Guidance
1

I have a functioning sketch that I am trying to graft into a Blynk sketch to gain easy networkability. My circuit is a Mega2560 w/Ethernet, a DHT sensor and an RTC. So far, I was able to get the DHT values sent to Blynk which displays the sensor readings in the Blynk app on my smartphone. I am now at the phase where I wish to also have my RTC values sent down stream, but have hit a roadblock. It was advised by the Blynk.cc founder to collect my RTC data into a string, but with my very limited knowledge in coding, I am unaware of how to do this and am seeking guidance, or more information than what is provided in the Arduino reference section. Below is the blocks in my sketch that queries my RTC and displays the hour according to 12 hour format. I created a local variable to capture that value and I wish to put this value, now.minute and now.second with respective colons in between into a string. Once I have the string, it will be much easier to forward the string to be displayed on my smartphone and I will be able to look in on my project and view climate conditions, project time and relay states.

void RTCdisplay()
    { 
//**********************************************************************************//
//****** Setting Time and testing to display 24 hour format as 12 hour format ******//
//**********************************************************************************//
      DateTime now = RTC.now();  // reads time at beginning of loop
  
      byte twelveHour = now.hour() - 12; // Variable used to display 13+ hours in 12 hour format
      byte zeroHour = 12;                // Variable use to convert "0" zero hour to display it as 12:00+
      byte displayHour();
  
      if (now.hour() == 0)  // First we test if the hour reads "0"
    { 
      zeroHour = displayHour();             
      Serial.print(zeroHour);  // if yes, serial print a "12" instead
      Serial.print(':');
      Serial.print(now.minute(), DEC);
      Serial.print(':');
      Serial.print(now.second(), DEC);
      Serial.print(' ');
      Serial.println (F("AM"));
    }
      else if (now.hour() >= 13)  // if no, Second we test if the hour reads "13 or more"
    { 
      twelveHour = displayHour();      
      Serial.print(twelveHour);   // if yes, serial print that current hour minus 12
      Serial.print(':');
      Serial.print(now.minute(), DEC);
      Serial.print(':');
      Serial.print(now.second(), DEC);
      Serial.print(' ');
      Serial.println (F("PM"));
    }
      else 
    {
      Serial.print(now.hour(), DEC);    // if no, Third we conclude that the am hours are being displayed correctly.
      Serial.print(':');
      Serial.print(now.minute(), DEC);
      Serial.print(':');
      Serial.print(now.second(), DEC);
      Serial.print(' ');
      Serial.println (F("AM"));
    }
    { 
      //Blynk.virtualWrite(V3, displayHour(), now.minute(), now.second()); 
      Serial.print(now.month(), DEC);
      Serial.print('/');
      Serial.print(now.day(), DEC);
      Serial.print('/');
      Serial.println(now.year(), DEC);
      Serial.println();
    }

Blynk.virtualWrite() is just my latest best guess how to send my data down, but it failed to compile and I commented it out until I figure out the proper course to take. Can someone please help me fill in some mental blank spots on this? Thank you in advance!

2

Your RTCdisplay() function appears to create variables for each element of the date and time that you want to turn into a string (lowercase s)

If so then look at the sprintf() function which will allow you to build a string consisting of values from variables and string literals such as ":". You can then use the string as you wish. A first stage would be to use sprintf() in a revised RTCdisplay() function to test the process.

3

Thank you for your assistance. In trying to dig up what I can on sprintf, I kept referring back to strings and chars and devised something of a solution by making 2 arrays of chars(?) to gather the variable values along with the traditional characters used (: or /), then referenced those with the Blynk.virtualWrite which then compiled. I never did find any literature on sprintf, but I think I no longer need to locate it as my troubles have been resolved.

void RTCdisplay()
    { 
//**********************************************************************************//
//****** Setting Time and testing to display 24 hour format as 12 hour format ******//
//**********************************************************************************//
      DateTime now = RTC.now();  // reads time at beginning of loop
  
      byte twelveHour = now.hour() - 12; // Variable used to display 13+ hours in 12 hour format
      byte zeroHour = 12;                // Variable use to convert "0" zero hour to display it as 12:00+
      byte displayHour;
      //char AM = "AM"
      //char PM = "PM"
  
      if (now.hour() == 0)  // First we test if the hour reads "0"
    { 
      displayHour = zeroHour;         
      //Serial.print(zeroHour);  // if yes, serial print a "12" instead
    }
      else if (now.hour() >= 13)  // if no, Second we test if the hour reads "13 or more"
    { 
      displayHour = twelveHour;      
      //Serial.print(twelveHour);   // if yes, serial print that current hour minus 12
    }
      else 
    { 
      displayHour = now.hour(); 
      //Serial.print(now.hour(), DEC);    // if no, Third we conclude that the am hours are being displayed correctly.
    }
    { 
      char timeStamp[6] = {displayHour, ':', now.minute(), ':', now.second()};
      char dateStamp[6] = {now.month(), '/', now.day(), '/', now.year()};
      Blynk.virtualWrite(V3, timeStamp);
      Blynk.virtualWrite(V4, dateStamp);
      //Serial.print(displayHour)
      //Serial.print(':');
      //Serial.print(now.minute(), DEC);
      //Serial.print(':');
      //Serial.print(now.second(), DEC);
      //Serial.print(' ');
      //Serial.println (F());
      //Serial.print(now.month(), DEC);
      //Serial.print('/');
      //Serial.print(now.day(), DEC);
      //Serial.print('/');
      //Serial.println(now.year(), DEC);
      //Serial.println();
    }
4

Just for future reference, here's a link to info on sprintf.