Arduinization of code

[safocl]

C_ESR_METER/C_ESR_METER.ino

Lines 868 to 876 in 657c600

	String flag = String(ESR_METER_FLAG);
	String flag_read = String("");
	char c = '\0';
	// Try to read ESR_METER_FLAG from EEPROM
	for (uint16_t i = 0; i < flag.length(); i++) {
	c = EEPROM.read(ESR_METER_FLAG_EEPROM_OFFSET + i);
	flag_read += c;
	}

and

C_ESR_METER/C_ESR_METER.ino

Lines 895 to 897 in 657c600

	for (uint16_t i = 0; i < flag.length(); i++) {
	EEPROM.write(ESR_METER_FLAG_EEPROM_OFFSET + i, flag[i]);
	}

maybe replace with:

const char flag[] = ESR_METER_FLAG;
char flag_read[sizeof(flag)] = {0};

EEPROM.get(ESR_METER_FLAG_EEPROM_OFFSET, flag_read);

and respectively

EEPROM.put(ESR_METER_FLAG_EEPROM_OFFSET, flag);

links:
https://docs.arduino.cc/learn/built-in-libraries/eeprom/#get
https://docs.arduino.cc/learn/built-in-libraries/eeprom/#put

[latchdevel]

This looks great!

I'm going to test it on actual hardware just to be fully confident about its correct behavior, and then I'll go ahead and merge the changes.

Thanks a lot!

[latchdevel]

Uppss....

The Arduino String class provides both the == operator and the equals() method, which behave identically.

https://docs.arduino.cc/built-in-examples/strings/StringComparisonOperators/

But, comparison between char[] arrays cannot be done using the == operator. Instead, specific functions like strcmp() or strncmp(), or even memcmp(), must be used to compare their contents.

https://github.com/safocl/C_ESR_METER/blob/ae1b7c7580a5f3094c7e325d0ac9ba931861b351/C_ESR_METER.ino#L874

The best option is to use strncmp() since the size of the array is known.

There's an additional issue to consider:

Previously, using flag.length() meant that 8 characters were read, written, and compared. However, in the updated version, sizeof(flag) returns 9 because char flag[] = ESR_METER_FLAG; includes the null terminator (\0) at the end.

This change breaks compatibility for users upgrading from older firmware versions, since their EEPROM data contains only the original 8 characters and lacks the null terminator at the ninth byte.

Fortunately, the fix is simple: subtract one byte from the comparison length to ensure only the original 8 characters are checked.

if (strncmp(flag, flag_read, sizeof(flag)-1) == 0)

Would you mind updating this part of the code?

Let me know if you need help with the change.
Thanks!

[safocl]

Uppss....

Yes... in normal C++ code, I would use std::ranges::equal and, accordingly, normal containers for such events -- but the Arduino API is quite sad, in my opinion. And doesn't deserve anyone's attention at all. Sadly, they reject the very idea of ​​using standard C++ library entities.

upd.
https://godbolt.org/z/h6MW3z4G3 -- example

[latchdevel]

Hi,

The compiler used by Arduino is avr-gcc which is based on C++11 and comes with a limited and reduced version of the C++ Standard Library. Neither std::ranges nor std::equal are available in the Arduino AVR toolchain.

There are also independent projects that aim to bring a more complete and modern subset of the C++ Standard Library to the AVR toolchain, like as:

• https://github.com/modm-io/avr-libstdcpp
• https://github.com/amanuellperez/mcu
• https://github.com/ETLCPP/etl

But, for this small use case, there's no need to overcomplicate things —strncmp() is more than enough.

Regards.