Unable to call String::indexOf with char* for a needle

[paulocsanz]

Hey I'm trying to avoid allocating+copying to search for a needle in a haystack. So it would be great if String provided a indexOf method that receives a char*.

Ideally it would provide a method for __FlashStringHelper, but since it uses asm/intrinsics to search I don't know if there is a way to do the search without ignoring that it's from PROGMEM. Is it possible?

Anyway I'm happy with just char*.

[paulocsanz]

I've went ahead and provided a String::indexOf for __FlashStringHelper pointers. And am calling strstr_P instead, as @earlephilhower showed me how.

[paulocsanz]

@earlephilhower @d-a-v

https://arduino-esp8266.readthedocs.io/en/latest/PROGMEM.html#functions-to-read-back-from-progmem

In the documentation (second paragraph of this section) it says it's UB to call strstr_P with a needle that's not from PROGMEM. So is the documentation wrong or is my code UB?

Should I restore the code to have the strstr_P path only for __FlashStringHelper and keep using strstr for the rest?

[earlephilhower]

If the documentation says that, it's wrong and we should fix it. Anything using PROGMEM is also safe to use RAM (but not vice-versa, of course!). The ESP8266 isn't like the AVRs where reads from PROGMEM require a special instruction. On the 8266 they just need to be 4-byte aligned and only 32-bits in size. The _P calls handle this behind the scenes.