compile error

[sslupsky]

Encountered the following error when attempting to compile a sketch using CmdMessenger:

Arduino-CmdMessenger/CmdMessenger.cpp:492:9: error: invalid conversion from 'char' to 'char*' [-fpermissive]
  return '\0';

The function is defined to return a pointer as follows;

Arduino-CmdMessenger/CmdMessenger.cpp

Line 484 in 8c3c444

char* CmdMessenger::readStringArg()

Since the function is returning a char instead of a pointer, this is causing a compiler error.

Should the correct return value be NULL? ie:

return NULL;

[sslupsky]

I am using the arduino CLI to compile.

arduino-cli Version: 0.3.7-alpha.preview

[sslupsky]

The target is a MKRWAN1300 that uses the SAMD21 mcu.

[ganjoe]

same with stm32duino

[adamj537]

This library appears to have been written for the AVR compiler, which does not return any errors on this line. Atmel SAM compilers return an error.

I was able to compile for an Adafruit Feather M0 by changing the offending line to include a cast, as follows:
return (char)'\0';

[CombiesGit]

original:

return '\0';

hmmm...:

return NULL;

better:

return nullptr;

[Erhannis]

original:

return '\0';

hmmm...:

return NULL;

better:

return nullptr;

Actually...that's a good point. Looking at the code, I think the author maybe intended to return an empty string - but instead effectively returned NULL. I'm not sure; I feel like it could go either way.

[ccrawford]

Using this code on an ESP32, I'm consistently getting crashes when readStringArg encounters the null value condition.

Actually, the crash happens on a call to CmdMessenger::unescape() that uses the (NULL) result of readStringArg(). Certainly we can write defensive code to check the value of readStringArg and not call unescape if the value is NULL, but I think either readStringArg should return a pointer to an empty string or unescape needs if(fromChar == NULL) return; before trying to dereference the null pointer.

If I add either or both of these simple changes, the crashes stop.

[coldfusioncoder]

Hitting this issue on MKR Zero, Arduino IDE 2.3.4.