Compilation error when enabling debug in Adafruit_PN532 lib

[jsiobj]

• Arduino board: Adafruit M0 Proto

• Arduino IDE version (found in Arduino -> About Arduino menu): Using VSCode + PlatformIO

• List the steps to reproduce the problem below (if possible attach a sketch or
  copy the sketch code in too):

When enabling debugging in Adafruit_PN532 lib uncommenting line 71/72

Adafruit-PN532/Adafruit_PN532.cpp

Lines 71 to 72 in 0bf3483

	// #define PN532DEBUG
	// #define MIFAREDEBUG

I get 2 compilation errors :
.pio\libdeps\adafruit_feather_m0\Adafruit PN532\Adafruit_PN532.cpp:957:28: error: invalid conversion from 'int8_t*' {aka 'signed char*'} to 'const byte*' {aka 'const unsigned char*'} [-fpermissive]

For compilation to succeed, I forced conversion to (const uint8_t*) for _uid and _key when calling PrintHex here :

Adafruit-PN532/Adafruit_PN532.cpp

Lines 881 to 888 in 0bf3483

	#ifdef MIFAREDEBUG
	PN532DEBUGPRINT.print(F("Trying to authenticate card "));
	Adafruit_PN532::PrintHex(_uid, _uidLen);
	PN532DEBUGPRINT.print(F("Using authentication KEY "));
	PN532DEBUGPRINT.print(keyNumber ? 'B' : 'A');
	PN532DEBUGPRINT.print(F(": "));
	Adafruit_PN532::PrintHex(_key, 6);
	#endif

With the change :

#ifdef MIFAREDEBUG
  PN532DEBUGPRINT.print(F("Trying to authenticate card "));
  Adafruit_PN532::PrintHex((const uint8_t*)_uid, _uidLen);
  PN532DEBUGPRINT.print(F("Using authentication KEY "));
  PN532DEBUGPRINT.print(keyNumber ? 'B' : 'A');
  PN532DEBUGPRINT.print(F(": "));
  Adafruit_PN532::PrintHex((const uint8_t*)_key, 6);
#endif

Not sure how to contribute / make a PR (code of conduct link in readme is broken)
and not even sure this is the proper way to solve this issue anyway.

Regards
Jean-Sébastien

[caternuson]

Also able to recreate this using Arduino IDE. Compiling the readMifareClassic library example for a target board of Feather M0:

Arduino/libraries/Adafruit-PN532/Adafruit_PN532.cpp:883:28: error: invalid conversion from 'int8_t*' {aka 'signed char*'} to 'const byte*' {aka 'const unsigned char*'} [-fpermissive]
  883 |   Adafruit_PN532::PrintHex(_uid, _uidLen);
      |                            ^~~~
      |                            |
      |                            int8_t* {aka signed char*}

[caternuson]

Not sure int8_t is a good choice for these in the first place. Not seeing any reasons for them being signed.

@jsiobj Try removing the casts. Then change the declarations in Adafruit_PN532.h to:

  uint8_t _uid[7];      // ISO14443A uid
  uint8_t _uidLen;      // uid len
  uint8_t _key[6];      // Mifare Classic key

That will most likely get past the compilation issue. But do other issue then arise? Like run time issues, etc?

[jsiobj]

Hello @caternuson,

Indeed, it passes compilation successfully. I'll do some tests, hopefully next week and give the results.

I did not want to change variables types in the first place as just debugging code was not working and I was not sure of the implications. But I agree that changing the type should be the way to go.