Unexpected output on Arduino

Question

I'm using Leonardo and I want to print a message when I type ">" and "<". Something like >my_message<.

I have the following code but it is not working like I was expecting (nothing happens). How can I fix this or is there a better way to do this?

String txtMsg = ""; // a string for incoming text

void setup() {
  Serial.begin(9600);
  while (!Serial); // wait for serial port to connect. Needed for Leonardo only
}

void loop() {
  // add any incoming characters to the String:
  while (Serial.available() > 0) {
    char inChar = Serial.read();
    txtMsg += inChar;

    char StartDelimiter = txtMsg.charAt(0);
    int endDel = txtMsg.length() - 1;
    char EndDelimiter = txtMsg.charAt(endDel);

    if (StartDelimiter == '>' && EndDelimiter == '<') {
      Serial.println(txtMsg);
    }
  }
}

"it is not working like I was expecting." - so what does it actually do? — us2012
– us2012, Commented Sep 8, 2013 at 0:41
Why don't you print what characters you are actually receiving? (As a means of debugging the problem, not a permanent solution) — Mats Petersson
– Mats Petersson, Commented Sep 8, 2013 at 0:51

Macattack · Accepted Answer · 2013-09-08 05:36:53Z

1

The problem was that your code looking for '>' always looked at character 0 and you were appending to your string, so after getting a first non '>' character you could never get to a condition in which you would print.

String txtMsg = ""; // a string for incoming text

void setup() {
    Serial.begin(9600);
    while (!Serial); // wait for serial port to connect. Needed for Leonardo only
}

void loop() {
    // add any incoming characters to the String:
    int got_start = 0;
    while (Serial.available() > 0) {
        char inChar = Serial.read();
        if (inChar == '>' && !got_start) {
            got_start = 1;
        }
        if (got_start) {
            txtMsg += inChar;
        }   
        if (inChar == '<' && got_start) {
            got_start = 0; 
            Serial.println(txtMsg);
            txtMsg = "";    
        }   
    }   
}

answered Sep 8, 2013 at 5:36

Macattack

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3 Comments

mafap Over a year ago

this is useful but is there any way to do that using charAt() function?

Macattack Over a year ago

@mafap Do you understand what was wrong with your existing code? You could use charAt() after you've appended to the string, but I'm not particularly sure why you would.

mafap Over a year ago

Now I understand. I wanted to use this function because I need to get the value of characters at different positions in a String. I just don't know what's the better way to do that.

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