[SOLVED] Trouble with serial writing

Projects Programming
1

Hello,

I'm having trouble with serial writing. Here is my code:

char buffer[10];

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

void loop() {
        if (Serial.available() > 0) {
                Serial.readBytesUntil('a',buffer,5);

                Serial.println(buffer);
        }
}

When I read, for example, "123a4" with the function readBytesUntil, I receive two messages: "123" and "423", ie, the Arduino is reading after the terminator and, for worse, it is keeping the buffer after reading until the terminator. What I want is something to read until the terminator and stop (and ensure that the buffer will be clean for the next reading)! I already tried to use the following statements, but it didn't work:

while (Serial.available ())
  Serial.read ();

Could someone help, please?

2

Perhaps you need to add code to clear the buffer between reads

if (Serial.available() > 0) {
                Serial.readBytesUntil('a',buffer,5);

                Serial.println(buffer);
                for (byte n = 0; n < 10; n++) {
                    buffer[n] = 0;
                 }
        }

...R

3

Robin2:
Perhaps you need to add code to clear the buffer between reads

if (Serial.available() > 0) {

Serial.readBytesUntil('a',buffer,5);

Serial.println(buffer);
                for (byte n = 0; n < 10; n++) {
                    buffer[n] = 0;
                 }
        }




...R

It did work for the buffer problem (thanks for that!), but I still have the problem with the reading after the terminator (now I have the messages "123" and "4" if I read "123a4").

4

The Serial method does read to the specified character, so you code is doing as it should, but not as you want. Try this mod:

   int bytesRead;
   char buffer[6];      // I misspelled this first time...

    if (Serial.available() > 0) {
      bytesRead = Serial.readBytesUntil('\n',buffer,5);
      buffer[bytesRead] = '\0';      // Make it a string
      Serial.println(buffer);
   }

Note that the code reads up to the newline character ('\n'), which is sent when the user clicks Enter or presses the Enter key. If you want to treat a char array as a string, you need to append a null termination character ('\0') to the end of the data. If you need to break out substrings, you can use indexof() and look for 'a'.

5

print and println expect null terminated c strings.

From the documentation.

Serial.readBytesUntil() returns the number of characters read into the buffer. A 0 means no valid data was found.

So a better fix is

void loop() {
        int len;
        if (Serial.available() > 0) {
                len=Serial.readBytesUntil('a',buffer,5);
                buffer[len]='\0'; // 0 is "null" in the context, bet i use the wrong  slash.
                Serial.println(buffer);
        }
}

Mark

6

You all helped me a lot. I used all you said and it works!

I just did this:

int bytesRead;
char buffer[10];
String strg;

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

void loop() {

  if (Serial.available() > 0) {
    bytesRead = Serial.readBytes(buffer,5);
    buffer[bytesRead] = '\0';
    strg = buffer;

    Serial.println(strg.substring(0,strg.indexOf('a')));
  }
}

Thanks a lot!