Reading multiple lines from serial - arduino

Question

I'm trying to get up to 64 lines of max 16 characters to display on an LCD screen via serial. These lines have to be given during startup. I've got the following, which works in most cases:
unsigned char textMatrix[64][17];
unsigned char lineCount = 0;
void readLines(){
Serial.println("Send up to 64 lines of up to 16 characters. Send an empty line to stop sending lines. Make sure to use \\n (newline) as line terminator!");
Serial.setTimeout(10000);
bool receiving = true;
while (receiving){
if(Serial.available() > 0) {
textMatrix[lineCount][0] = '\0';
char res = Serial.readBytesUntil('\n',textMatrix[lineCount],16);
if (res == 0){
if (textMatrix[lineCount][0] != '\0'){
continue;
}
Serial.println("Received empty line");
receiving = false;
break;
}
textMatrix[lineCount][16] = '\0';
Serial.print("Received line: ");
Serial.println((const char*)textMatrix[lineCount]);
lineCount++;
if (lineCount >= 63){
receiving = false;
}
}
}
}
The problem occurs when I send the following line:
Okay, that's one
This line is exactly 16 characters long. I'm assuming that this causes readBytesUntil to trigger twice, causing it to be the same as pressing enter twice. I don't seem to be able to find a difference between seriously sending an empty line or sending a line of exactly 16 characters. What would be the best way to resolve this?

Answer 1

When you send the line
Okay, that's one
That's not 16 character but 17, because there is \n character in the end. What Serial.readBytesUntil('\n',textMatrix[lineCount],16); does in this case is it takes out first 16 characters out of the buffer. After that operation, the only thing left there, is the new line \n, which in the next iteration of the loop is read as an empty line.
To counter that, you can check res variable, and if you see that it equals 16, discard the next read. Or do some more checks in case there is a string longer than 16 + new line.

Answer 2

Here's one way... just read the chars yourself:
unsigned char textMatrix[64][17];
const uint8_t MAX_WIDTH = sizeof( textMatrix[0] );
const uint8_t MAX_LINES = sizeof( textMatrix ) / MAX_WIDTH;
unsigned char lineCount = 0;
void readLines(){
uint32_t startTime = millis();
uint8_t column = 0;
do {
if (Serial.available()) {
char c = Serial.read();
if (c == '\n') {
if ((lineCount >= MAX_LINES) || (column == 0))
break; // too many lines or empty line
textMatrix[ lineCount ] [ column ] = '\0'; // NUL-terminate
lineCount++; // start accumulating a new line
column = 0;
} else if (column < MAX_WIDTH-1) {
// room for another char on this line
textMatrix[ lineCount ] [ column ] = c;
column++;
} // else
// ignore rest of line
}
} while (millis() - startTime < 10000UL); // TIMEOUT == 10s
} // readLines