Update ostream

[pischky]

allow use of F() macro for strings:
cout << F("Hello") << endl;

[mike-matera]

Thank you so much! I just have a question about a couple of lines.

[matthijskooijman]

Looks like an interesting change. I left some suggestions inline.

[matthijskooijman]

I would consider leaving out these include guards, since pretty much every (non-AVR) Arduino core provides dummy version of the F() macro and pgm_read_byte and friends, so adding this code unconditionally makes user code that uses F() and ArduinoSTL more portable.

[pischky]

Ok, but this code will not run on other than AVR. avr/pgmspace.h is required to read from flash.

[matthijskooijman]

Ok, but this code will not run on other than AVR. avr/pgmspace.h is required to read from flash.

Most cores actually provide a dummy avr/pgmspace.h, so portable sketches can still use F() (etc.) and compile on non-AVR too. E.g. see https://github.com/arduino/ArduinoCore-sam/tree/master/cores/arduino/avr and https://github.com/stm32duino/Arduino_Core_STM32/tree/main/cores/arduino/avr (better to just include Arduino.h instead, though, since that should also include pgmspace or its dummy).

[pischky]

I understand. Code for SAM and STM should compile without complaning about missing F() macro

[matthijskooijman]

Probably better to just #include <Arduino.h>, which should include both of these in a more portable way (at the expense of incuding more than maybe needed).

[matthijskooijman]

Is this specialization really needed? It looks like the implementation is identical to the generate charT version above, so it can probably be omitted?

[pischky]

Hmm....
I thing I do not understand what's your question. This is the trick for strings in flash memory.
AFAIK there must be different code for strings from RAM and strings from FLASH. For flash pgm_read_byte() hast to be used.
I have tested this on ATmega328P. May be we have to thing again for newer chips like ATmega4809. They are "Von Neumann" and do not need the pgm_read_byte().

[matthijskooijman]

I mean that the implementation of this specialization:

ArduinoSTL/src/ostream

Lines 442 to 458 in f426344

	#ifdef ARDUINO_ARCH_AVR
	//support strings from flash memory [PI]
	//stolen from Arduino Print.cpp
	//sample use: cout << F("Hello") << endl;
	template<class traits> _UCXXEXPORT basic_ostream<char,traits>&
	operator<<(basic_ostream<char,traits>& out, const __FlashStringHelper* c) //[PI: New] stolen from Arduino Print.cpp
	{
	typename basic_ostream<char,traits>::sentry s(out);
	PGM_P p = reinterpret_cast<PGM_P>(c);
	while (true) {
	char x = pgm_read_byte(p++);
	if (x == 0) break;
	out.put(x);
	}
	return out;
	}
	#endif

Is identical to this specialization:

ArduinoSTL/src/ostream

Lines 415 to 431 in f426344

	#ifdef ARDUINO_ARCH_AVR
	//support strings from flash memory [PI]
	//stolen from Arduino Print.cpp
	//sample use: cout << F("Hello") << endl;
	template<class charT, class traits> _UCXXEXPORT basic_ostream<charT,traits>&
	operator<<(basic_ostream<charT,traits>& out, const __FlashStringHelper* c)
	{
	typename basic_ostream<charT,traits>::sentry s(out);
	PGM_P p = reinterpret_cast<PGM_P>(c);
	while (true) {
	charT x = pgm_read_byte(p++);
	if (x == 0) break;
	out.put(x);
	}
	return out;
	}
	#endif

So I think the first one is redundant and should be caught by the second one (with charT = char)?

[pischky]

May be Mike just copied some of my code...
Should test again if Mikes code is working in my case.