Support printing constant strings containing nulls

[eric-wieser]

What's changed

1. Serial.print("Hello""\0""World")
   • Before: prints Hello
   • After: prints Hello\0World
2. Serial.print("Hello")
   • Before: invokes strlen
   • After: does not, is faster. Code size should be unchanged
3. Serial.println("Hello")
   • Before: invokes strlen
   • After: does not, is faster. Slightly increased code size, due to inlining

Thoughts?

[matthijskooijman]

I'm not so sure if this is really a good idea, since now:

write("foo\0bar");

and

char *ptr = "foo\0bar";
write(ptr);

Will have different results and I'm not sure that's really a good idea.

Also, I think that:

char buf[10];
buf[0] = 'X';
buf[1] = '\0';
write(buf);

will now print 10 bytes, even though only 2 is intended. Since this sort of thing is likely to occur in sketches, this breaks compatibility.

Regarding handling of strings with embedded zeroes, you might be interested in #1936 which improves the String class to better handle them.

[PaulStoffregen]

Thoughts?

Isn't this what write(buf, length) is supposed to do?

Ideally, both write() functions ought to take (const void *) type, but whether even that can be considered changeable at this late stage in Arduino's development is a good question?

[eric-wieser]

I think that [...] will now print 10 bytes, even though only 2 is intended. Since this sort of thing is likely to occur in sketches, this breaks compatibility.

Yep, you're right - this is not an acceptable change