Does Serial.find Clears Buffer If It Can't Find Anything - c++

Question

I'm trying to look for keywords in serial buffer in Arduino.
if (Serial.find("SOMETHING"))
{
// do something
}
else if (Serial.find("SOMETHING ELSE"))
{
// do another thing
}
But only the first if works. Even if I send "SOMETHINGELSE" it doesn't check at all. Does find function clear buffer completely even if it can't find anything ? If yes, what can i do in this situation?

Answer 1

Serial.find(); reads Serial buffer and removes every single byte from it, up to the point where it can find specified by you String or Character.
If you use it in an conditional statement like in your example, it will always find "SOMETHING" even if "SOMETHING ELSE" exist because everything up to the point of "SOMETHING" is removed from buffer ( if "SOMETHING" actually arrived before "SOMETHING ELSE" ).
If we assume that your data arrives in order SOMETHING and then SOMETHING ELSE, your Serial buffer will look like this: SOMETHING ELSESOMETHING
in which case:
It will find "SOMETHING" and stop in there as first condition to meet is to search for this word exactly.
I assumed that you don't actually mean to send "SOMETHING" so lets say that first String to look for is StringA and then StringB. Your buffer then will look like this: StringBStringA however based on your conditional statement it will still only find StringA. This will happen because StringA still exist in buffer and now when first condition is checked you basically ask to search for StringA and by doing this you are removing StringB using Serial.find(StringA) - it simply skips StringB because its not aware that you are going to ask about it in your else if later on.
Solution to your problem depends on data that you expect to receive. You can tag beginning of data that you are awaiting for with some specific character or sequence of characters:
For example lets assume that you await for String type of data. Before you send it to your Serial put each message in a specific format like $START$SOMETHING$
You can then use this to find first command that starts with your tag and load content of the message to String so you can compare it with expected results using conditional statement.
Note!!! Code below will stop on first message with $START$ tag so if you want to look into your Serial buffer for other messages you don't want to break while(Serial.available > 0) and use arrays to store each result.
char myCharacter;
String myIncomingData;
if(Serial.find("$START$"))
{
while (Serial.available() > 0) {
// Reads byte of Serial at the time
myCharacter = Serial.read();
// Stops at the end of data
if (myCharacter == "$") {
break;
}
// Adds each character to String with your data
myIncomingData += myCharacter;
}
if (myIncomingData == "SOMETHING") {
// Do whatever you like to with your data
} else if (myIncomingData == "SOMETHING ELSE") {
// Do whatever you like to with your data
}
I would use this solution only if you want to use Serial.find(), Im sure that you can get your results in many different ways as well, at the end you can always go through entire 64 bytes of you buffer byte by byte using your own code :D.