How to convert byte array into a single variable

Question

In this code i am taking the TID data(20bytes of 160bits) in the form of array according documentation and and its working correctly and getting the output of RFID tags.

Now I just need your guidance that how can i convert the array of 20 Bytes into a single variable or into a double long datatype? or another. Because I have to push it on to my MySQL database server for further processing.

I had tried the following code which works fine

byte x[10] = "450210921";
long result = atol(x);
Serial.print("long value of the byte is: ");
Serial.println(result);

but when i put the above code into my main code, getting not any error and I am not getting the required output.!

void setup()
{
 Serial.begin(115200);
}
void loop()
{
 byte response;
 byte myTID[20]; //TIDs are 20 bytes
 byte tidLength = sizeof(myTID);
 //Read unique ID of tag
 response = nano.readTID(myTID, tidLength);
 if (response == RESPONSE_SUCCESS)
 {
 for(byte x = 0 ; x < tidLength ; x++)
 {
 if(myTID[x] < 0x10) Serial.print("0");
 /*temp[x]=(myTID[x], HEX);*/
 //Swapping values into temp variable
 temp[x]=myTID[x]; 
 Serial.print(temp[x]);
 }
 /*byte x[10] = "450210921";*/
 //Convert a whole array into a single long variable
 long result = atol(temp);
 Serial.print("long value of the byte is: ");
 Serial.println(result);
 }
 else
 Serial.println("Failed read");
}

• Majenko: There is no such thing as a single variable that is 160 bits in size. I think you want to format the bytes as a string (and there are plenty of questions about that on here).
• Eza: Ok @Majenko but is there any way to push complete an array to MySQL into a single table cell using nodemcu?
• Majenko: I have no idea about the MySQL side of things, but you can take each byte in the array, turn it into a text representation of a hexadecimal pair, concatenate them all in a string, and use that string.
• Majenko: arduino.stackexchange.com/questions/53258/…
• Mikael Patel: There are several simple errors: 1) "atol(x)" should be "atol(tmp)", 2) but then "tmp" should be null-terminated, 3) which then implies that it is too short. And so on.

Answer 1

You can't convert 20 bytes to long. Send it as string of hex values. A byte takes two characters in hex, so you will send a 40 characters string, which can be simply decoded back to bytes.

char str[sizeof(myTID) * 2 + 1];
const char* hex = "0123456789ABCDEF";
for (int i = 0; i < sizeof(myTID); i++) {
 str[i * 2] = hex[(myTID[i] >> 4)];
 str[i * 2 + 1] = hex[(myTID[i] & 0x0F)];
}
str[sizeof(str)] = 0;
Serial.println(str);

• Eza: It works! Thank, what about for this for(byte x = 0 ; x < sizeof(myTID) ; x++) { content.concat(String(myTID[x] < 0x10 ? " 0" : " ")); content.concat(String(myTID[x], HEX)); } content.toUpperCase(); softSerial.print(content)
• Juraj: String is not good
• Eza: Could you explain it that how the string is not good!!
• Juraj: hackingmajenkoblog.wordpress.com/2016/02/04/…