Print.h add printf API

[iZhangHui]

Describe the request

Please add a printf function to the Print class.

ArduinoCore-API version

0f4e57e

Additional context

Additional requests

• Add support for printf, stdio, etc. [imported] #41
• Add printf patch to print?  #53
• https://groups.google.com/a/arduino.cc/g/developers/c/E0pUPWeDE2Y/m/fGBK_49bBgAJ
• please enhance Serial by a printf() method like ANSI C printf! Arduino#3586
• Add function "printf" to AVR core class "print" Arduino#5938
• Printf.... Why after 5 year of people asking for it, we can't find a way to add it!!! Arduino#7386
• ESP core printf implementation in AVR core. ArduinoCore-avr#482
• Feature request - Implement Serial.printf()  ArduinoCore-mbed#941
• Added printf to Print class to have Serial.printf() functionality ArduinoCore-samd#458
• core: serial: implement Serial.printf() ArduinoCore-zephyr#305

Related

• Enabling printf style output method with variadic arguments #29
• Improved print formatting #34
• https://groups.google.com/a/arduino.cc/d/msg/developers/E0pUPWeDE2Y/GPWl9Nw1BwAJ
• Add printf to print class SpenceKonde/megaTinyCore#112

[cousteaulecommandant]

See #28

[matthijskooijman]

Adding printf seems obvious, but in the past, adding printf support has been discussed (on the mailinglist, I think, I don't have a link at hand), and the main (and so far, I think, decisive) argument against adding printf is that it is convenient, but not a very transparent API for the novice programmer audience. Also, lack of type safety makes it very easy to get hard-to-debug problems using printf. Of course, you could argue that this API is available for more advanced programmers that need it, but if it is offered by default, it will likely going to end up in examples that novice programmers use too and end up causing problems anyway. If an expert user really wants to use printf, there are some libraries that offer a similar thing as well.

Also see the discussion in #28 for some links to previous discussions.

Ideally, some more type-safe and convenient way of printing multiple values would be available (and I've been working on something a long time ago based on a variadic print function), but nothing definitive has come out of that so far. The issue for implementing something better is #34.

I'm not sure if the stance on this has changed, but personally I would very much prefer something that is better to use than plain printf (and with new C++ features, implementing something that is convenient and type-safe is probably more feasible than when printf was conceived).

There currently seem to be two PRs implementing this: #29, which prints byte-by-byte, and #28 which keeps a fixed-size buffer on the stack (which IMHO is needlessly limiting, so I closed it).