Comparing Strings with serialEvent

Hello, I must be doing something stupid with my Mega2560 (Arduino 1.0.1) when trying to test a String that's input using the serialEvent example with my own strings. In the example below, checkMystring() always returns 'String not found'. I've tried all sorts of variations. Perhaps I can't get my head round the object/variable/constant uncertainty that seems to surround the Arduino String object, at least in the minds of newbies.

/* Serial Event example

When new serial data arrives, this sketch adds it to a String. When a newline is received, the loop prints the string and clears it.

A good test for this is to try it with a GPS receiver that sends out NMEA 0183 sentences.

Created 9 May 2011 by Tom Igoe

This example code is in the public domain.

http://www.arduino.cc/en/Tutorial/SerialEvent

*/

String inputString = ""; // a string to hold incoming data boolean stringComplete = false; // whether the string is complete // Can't get these commented-out ones to work: //String myString = String("chris"); //String myString = "chris"; String myString1;

void setup() { // initialize serial: Serial.begin(9600); // reserve 200 bytes for the inputString: inputString.reserve(200); myString1 = String("chris"); }

void loop() { // print the string when a newline arrives: if (stringComplete) { checkMystring(); Serial.println(inputString); // clear the string: inputString = ""; stringComplete = false; } }

void checkMystring() { // if (inputString == myString1) .. doesn't work either if (inputString.equalsIgnoreCase(myString1)) {Serial.println("Matches"); } else {Serial.println("Match not found"); } }

/* SerialEvent occurs whenever a new data comes in the hardware serial RX. This routine is run between each time loop() runs, so using delay inside loop can delay response. Multiple bytes of data may be available. / void serialEvent() { while (Serial.available()) { // get the new byte: char inChar = (char)Serial*.read(); // add it to the inputString: inputString += inChar; // if the incoming character is a newline, set a flag // so the main loop can do something about it: if (inChar == '\n') { stringComplete = true; } } }

Notice that you append the carriage return onto the String, but the to be compared to String does not have a carriage return.

Also, notice that you do not return when the carriage return arrives. So, you append the line feed, too, if you are appending both in the Serial Monitor.

About String initialization, I've just tried this:

String str1("first string");
String str2("second string");

void setup() {
    Serial.begin(115200);    
}


void loop() {
    Serial.print("str1=");
    Serial.println(str1);
    Serial.print("str2=");
    Serial.println(str2);
    
    delay(2000);
}

About String initialization, I've just tried this

And? It worked? It fell flat on its face? It laughed at you? It went up in smoke?

It was just an answer to these comments:

// Can't get these commented-out ones to work:
//String myString = String("chris");
//String myString = "chris";

And? It worked? It fell flat on its face? It laughed at you? It went up in smoke?

You're certainly able to compile and run it, and see for yourself what happens.

Many thanks PaulS. I suppose you could change the order of commands in void serialEvent() so the newline doesn't get appended to inputString, but presume the author had reasons for not doing that. A bit of browsing turns up method trim() which does the job nicely. Here's my corrected and tested version, with "chris" declared as though it were a constant:

/*
  Serial Event example, with addition by crlMIDI

 When new serial data arrives, this sketch adds it to a String.
 When a newline is received, the loop prints the string and 
 clears it.

 A good test for this is to try it with a GPS receiver 
 that sends out NMEA 0183 sentences. 

 Created 9 May 2011
 by Tom Igoe

 This example code is in the public domain.

 http://www.arduino.cc/en/Tutorial/SerialEvent

 */

String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;  // whether the string is complete
// the string we are going to compare inputString with
String myString1 = "chris";

void  setup() {
  // initialize serial:
  Serial.begin(9600);
  // reserve 200 bytes for the inputString:
  inputString.reserve(200);
}

void loop() {
  // print the string when a newline arrives:
  if (stringComplete) {
    checkMystring();
    Serial.println(inputString);
    // clear the string:
    inputString = "";
    stringComplete = false;
  } 
}
  
  void checkMystring() {
    // trim is a method of the String class that removes whitespace
    // including Newline and Carrriage return
    inputString.trim(); 
    // either of the following 2 commands is OK:
     if (inputString == myString1) 
    // if (inputString.equalsIgnoreCase(myString1))
      {Serial.println("Matches"); }
    else {Serial.println("Match not found"); }  
}

/*
  SerialEvent occurs whenever a new data comes in the
 hardware serial RX.  This routine is run between each
 time loop() runs, so using delay inside loop can delay
 response.  Multiple bytes of data may be available.
 */
void serialEvent() {
  while (Serial.available()) {
    // get the new byte:
    char inChar = (char)Serial.read(); 
    // add it to the inputString:
    inputString += inChar;
    // if the incoming character is a newline, set a flag
    // so the main loop can do something about it:
    if (inChar == '\n') {
      stringComplete = true;
    } 
  }
}