What's the most direct way to assign Serial.read() bytes to an array?

Question

I'm trying to send NMEA 0183 sentences through LoRa. Every dinstict NMEA message looks like several char arrays (sentences) followed by '\n'. In the below picture we see one NMEA distinct message:

This message arrives in the Arduino input buffer every 1 second with differentiated values (numbers) and it has to be sent over LoRa as fast as possible. In order to send it over LoRa I need to read all bytes on the input buffer and assign them to an array and send them as an array, not one by one. I know that Serial.read() reads only one byte, and that's the problem. How can I read all bytes and send them as a whole?

This is my code:

  if (Serial.available()) {
     c = Serial.read();
     rf95.send((char *)c, sizeof(c));
     rf95.waitPacketSent();

I use RadioHead library, and the definition of rf.95.send is: RH_RF95::send (const uint8_t * data, uint8_t len)

c is of char type.

Answer 1

@DataFiddler suggested something like readBytesUntil. In fact, you can just use readBytesUntil. It returns either when timeout happens or when you reach the specified terminator. It consumes, but does not include the terminator. The timeout defaults to 1000 milliseconds, and can be modified with the setTimeout() method.

One downside is that you can't differentiate timeout, full buffer, and terminator reached. This shouldn't be a problem except for serial transmission errors. If your data is coming in at the NMEA standard 4800 baud, you could reasonably change the timeout to 5 milliseconds and still work.

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One thing that might bite you, is the line:

     rf95.send((char *)c, sizeof(c));

It is a mistake to cast the first parameter. The error you got indicated you should write:

     rf95.send(&c, sizeof(c));

But the sizeof is also wrong. The return type of Serial::read() is int, in part because there are 257 possible values. If you declared c as an int, its size would be 2, not 1.

In any case, if you are using readBytesUntil, you pass the same buffer you passed it to rf95.send(), and the return value from the first as the second parameter of the second.

Answer 2

All more complex Serial reading methods are based on read().

Luckily there's a terminating character '\n' in your case, so you can implement something similar to readBytesUntil by yourself, if you want to.

Answer 3

I was missing a null termination character. That got me reading garbage from all over the buffer. Adding a '0' at the end of the buffer's length is mandatory. Plus, as David G. noticed, sizeof() function is incorrect. strlen() must be used.