10 years, 3 months ago.

The problem is exactly what the error is telling you is wrong, rfid.read() is an integer. socket.send() expects a char * or char[]. You either need to convert the number to a string if you want to send it as text or cast it to a char* if you want to send it as binary data.

Also you do 3 rfid reads, they could give you different values or lock things up while waiting for a new read. It's far safer to read once and store the result.

If you want to send it as binary then it should be

if (rfid.readable()) {
  // only read once so that we can't display one value and then send a different one over the network if two cards are close
  int value = rfid.read(); 
  lcd.printf("RFID tag number: %d\n",value);
  socket.send_all( (char *)&value, sizeof(value));
}

To send text you would do

if (rfid.readable()) {
  // only read once so that we can't display one value and then send a different one over the network if two cards are close
  int value = rfid.read(); 
  char valueString[10];  // a single 16 or 32 bit number should never go over 9 characters so this size should always be big enough.
  int stringLen = snprintf(valueString, 10, "%d", value); // convert number to string
  lcd.printf("RFID tag number: %s\n",valueString);  // use the string version for the lcd, saves converting it twice.
  socket.send_all( valueString, stringLen);
}

If you are using scanf() or something similar to read the data at the other end of the network link then it may make sense to include a \n at the end of the network data by adding it to line 5 above and then removing it from line 6.

In the future rather than using a screen shot to include code put <<code>> on a new line before the code and <</code>> after it.