Document F() macro for placing constant strings in program (flash) memory.

[damellis]

You can use the F() macro to place constants in flash memory, not RAM, e.g. Serial.println(F("foo")) but I didn't find this documented anywhere in the Arduino reference.

[matthijskooijman]

The use of the __FlashStringHelper* type for storing such constants should probably also be documented.

On a related note, the http://arduino.cc/en/Reference/PROGMEM should also be updated. Since the gcc and libc upgrade in 1.5.7 (IIRC), there is no need to use the prog_* types anymore.

[q2dg]

It is documented in http://playground.arduino.cc/Learning/Memory... but it's not an official documentation, I infer. This fact is very inconsistent because while in http://arduino.cc/en/Reference/PROGMEM (official resource) the issue with new PROGMEM way of doing things is updated (see #2647), in http://playground.arduino.cc/Main/PROGMEM is not...so...mmm...

See also #2122

[agdl]

@q2dg @damellis documentation added for Serial.print(F()) added https://www.arduino.cc/en/Reference/PROGMEM

@matthijskooijman how do you suggest to modify the current documentation?

[q2dg]

• There's some typo ("istruction" , the comma between "to be printed" and "is normally"...)
• Maybe behind "PROGMEM is part of the pgmspace.h library" sentence I would specify "which is only available in AVR architecture"
• The paragraph talking about F() is placed in a nonsense way. It should be better written (with a proper title, like 'The F() macro' or similar) at the end of all text.

[agdl]

@q2dg modified in the way you suggested

[q2dg]

Ok, thanks. For me it's already right

[agdl]

ok, @matthijskooijman can this be closed?

[agdl]

I'm closing this, reopen it if necessary