String to char array one character too short

Projects Programming
1

I'm working with a Bluetooth module (HC-05) connected to the Arduino (Mega 2560). With my android device I'm sending commands to the Arduino. I use this code to receive the data:

String message;

void readDataFromBluetooth() {
	if(btSerial.available()) {
		while(btSerial.available()) {
			message += char(btSerial.read());
		}
		
		char command[message.length()];
		message.toCharArray(command, message.length());

		// debug
		String replyStr = message + " - " + String(receivedMessage.length())+ " - "+ String(command)+ " - "+ String(strlen(command));
		Serial.println(replyStr);

		message = "";
		processCommand(command); // a method where I use strcmp to compare and execute the necessary code
	}
}

As you can see I'm printing the results for debugging, and I've noticed that the char array command is a character short in respect to the string message. For example, if I send "HELLO" from Android, message will be "HELLO", but command will be "HELL". So in the Serial Monitor I'll see something like:
HELLO - 5 - HELL - 4

What am I doing wrong?

3

I've tryed that, nothing changed, same problem :frowning:
I've even trye to give a much bigger size to command, but nothing change. :frowning:

4

I've tryed that, nothing changed, same problem

But different code, which we can't see.

I can't really see the point of using String, if all you want is a string.

5

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data.

The use of while(btSerial.available()) { often fails because the Arduino can empty the buffer faster than characters arrive.

...R

6

Thank you for the link, your method to receive multiple characters worked great! :slight_smile:

Anyway, I've just found what was missing on my original post code: after the while-loop ended, we need to add the termination character to the String.

message += '\0';

Note the '\0'. If you use "\0" it won't work.

After that the method toCharArray works great.

7

Davide_sd:

	if(btSerial.available()) {

	while(btSerial.available()) {
		message += char(btSerial.read());
	}
	
	char command[message.length()];
	message.toCharArray(command, message.length());



What am I doing wrong?

You are using serial.available() to find the end of the command string, rather than parsing the incoming data.

Just because there are not character incoming right now, does not mean that there won't be more coming down the pipe in another millisecond, and does not mean that the message (whatever it is) is definitely finished. Maybe there's nothing on the serial right now because the data is buffered. Maybe there's nothing there because you set the serial to 9600, and that's actually pretty slow (one character per 1.04 milliseconds).

You have to work out a way of figuring out when the command is finished like looking for a space or a newline. You can't rely on Serial.available() to do that job.[/code]

8

Quick questions:

  1. do you have control over the format the command is being sent in?

  2. can you provide an example of the command being sent?

  3. what do you want to do with the data that is received?