Weirdness using altSerial on Uno

Using Arduino Programming Questions
1

I am using the altSerial library on an Uno and I get an error when I try to write a zero.

altSerial.write (0)

or

altSerial.write (0x00)

Assigning a zero to a variable and then writing the variable works.

Writing any value other than zero also works.

Is this a bug in the altSerial library or am I missing something?

Sorry if this is a noob question but I am a noob :confused:

edit: ya, I guess the error message would be nice DOH!

Arduino: 1.6.5 (Linux), Board: "Arduino Uno"

IO_Expander_2.ino: In function 'void loop()':
IO_Expander_2:1479: error: call of overloaded 'write(int)' is ambiguous
IO_Expander_2.ino:1479:35: note: candidates are:
In file included from IO_Expander_2.ino:2:0:
/home/jim/Arduino/libraries/AltSoftSerial/AltSoftSerial.h:53:9: note: virtual size_t AltSoftSerial::write(uint8_t)
size_t write(uint8_t byte) { writeByte(byte); return 1; }
^
In file included from /home/jim/Arduino/hardware/arduino/avr/cores/arduino/Stream.h:26:0,
from /home/jim/Arduino/hardware/arduino/avr/cores/arduino/HardwareSerial.h:29,
from /home/jim/Arduino/hardware/arduino/avr/cores/arduino/Arduino.h:224,
from /home/jim/Arduino/libraries/AltSoftSerial/AltSoftSerial.h:30,
from IO_Expander_2.ino:2:
/home/jim/Arduino/hardware/arduino/avr/cores/arduino/Print.h:49:12: note: size_t Print::write(const char*)
size_t write(const char *str) {
^
call of overloaded 'write(int)' is ambiguous

2

What's the error you get? Dontcha think that might be important? Or shall we just guess at it?

3

It's not just altSerial. All the stream-based classes do it. Here's two ways...

const byte ZERO = 0;
...
  Serial.write(ZERO);  //method 1, not used very often as you don't normally need a name for zero
  Serial.write((byte)0); //method 2. Kinda klunky but it works
4

Thanks for confirming what I suspected. +1 for you :slight_smile:

5

The clue is here:

IO_Expander_2.ino: In function 'void loop()':
IO_Expander_2:1479: error: call of overloaded 'write(int)' is ambiguous

When altSerial.write(...) is called with a variable, the type of the variable determines which overloaded version to call. When altSerial.write(...) is called with a zero, the zero could be a byte, an int, a pointer, etc.

Why this works with other values I don't know. 259 is obviously not a byte, but the poster didn't tell us what other values work.

In any case, to force the behavior, cast the zero to an appropriate type. For example:
altSerial.write((int)0) ;