Unable to clear the string

Using Arduino Programming Questions
#1

Hello to everyone :slight_smile:
I am writing a code that is very simple but I have some problems with strings. Here is the code:

boolean stringComplete = false;
String inputString = "";

void setup() {
  Serial.begin(9600);
  inputString.reserve(20);
}

void loop() {

  if(stringComplete){
    
    Serial.println(inputString);
    Serial.println(inputString.length());
    
    Serial.println(inputString[0]);
    Serial.println(inputString[1]);
    Serial.println(inputString[2]);
    Serial.println(inputString[3]);
    Serial.println(inputString[4]);    
    
    inputString = "";
    
    stringComplete = false;
  }
}


void serialEvent() {
  while (Serial.available()) {

    char inChar = (char)Serial.read(); 

    inputString += inChar;
   
    if(inChar == '>') {
      stringComplete = true;
    } 
  }
}

From another Arduino Uno I am sending 5 bytes like this for example: . Only when first string is completed I get correct string which length is 5. But all the others strings are length of 7, somehow I get additional two chars in the begining of the received string.
Lines:

    Serial.println(inputString[0]);
    Serial.println(inputString[1]);
    Serial.println(inputString[2]);
    Serial.println(inputString[3]);
    Serial.println(inputString[4]);

are giving me the next result:

<
A
2

Can you see the solution to this problem? Thanks in advance!

#2

First, your post title is wrong. Second, the body of your post contains many errors. You are not having problems with strings. You are having problems due to misusing Strings.

A String is an object that wraps a NULL terminated array of chars. The wrapper offers little benefit, but causes many problems.

So NULL terminated array means that the NULL is a stop sign. Stop processing the data in the array when you get here, You failed to stop at the stop sign.

#3

Thank you for your answer, I see it more clearly now. I am sorry for mistakes that I have made, next time I will be more carefull :slight_smile:

#4

next time I will be more careful

Especially stopping at stop signs. Blowing a stop sign could get you killed.

#5

PaulS:
A String is an object that wraps a NULL terminated array of chars.

O.M.G!!! The light is coming on for PaulS! 8)

#6

Not sure what your end product is going to be, but below is a method of capturing a string of characters sent from the serial monitor using a comma to indicate the end of the characters being sent.

//zoomkat 3-5-12 simple delimited ',' string  
//from serial port input (via serial monitor)
//and print result out serial port

String readString;

void setup() {
  Serial.begin(9600);
  Serial.println("serial delimit test 1.0"); // so I can keep track of what is loaded
}

void loop() {

  //expect a string like wer,qwe rty,123 456,hyre kjhg,
  //or like hello world,who are you?,bye!,
  
  if (Serial.available())  {
    char c = Serial.read();  //gets one byte from serial buffer
    if (c == ',') {
      //do stuff
      Serial.println(readString); //prints string to serial port out
      readString=""; //clears variable for new input      
     }  
    else {     
      readString += c; //makes the string readString
    }
  }
}
#7
#8

O.M.G!!! The light is coming on for PaulS!

Oh geez. You leave out "uselessly" once and some people think that means you accepts crutches as valid.

#9

zoomkat:
O.M.G!!! The light is coming on for PaulS! 8)

Better read this, zoomkat:

Method      Time   Memory   Sketch
              µS    Used     Size
            
C-string      44     517      1782
STL string   468     554      2994
String      2480     526      3746

So, String is fine, if you don't mind it taking 2480/44 times as long (56 times as long). And risk memory fragmentation.

#10