"ordered comparison of pointer with integer zero" error ArduinoIDE / ESP32

[CnczubehoerEu]

Step 1: Describe your environment

• OS version: Windows 11
• Arduino IDE version: 2.3.2
• MFRC522 Library version: 1.4.11
• Arduino device: DOIT ESP32 DEVKIT V1
• MFRC522 device: MFRC522 (??)

Step 2: Describe the problem

My ESP32 with MFRC522 worked well for a very long time. I put my work on hold for a few months and wanted to get back to it today. I pressed "verify" on the since the last work few month ago code and now the following error appears:

XYZ\Arduino\libraries\MFRC522\src\MFRC522Extended.cpp: In member function 'MFRC522::StatusCode MFRC522Extended::TCL_Transceive(TagInfo*, byte*, byte, byte*, byte*)':
XYZ\Arduino\libraries\MFRC522\src\MFRC522Extended.cpp:824:34: error: ordered comparison of pointer with integer zero ('byte*' {aka 'unsigned char*'} and 'int')
824 | if (backData && (backLen > 0)) {
| ~~~~~~~~^~~
XYZ\Arduino\libraries\MFRC522\src\MFRC522Extended.cpp:847:42: error: ordered comparison of pointer with integer zero ('byte*' {aka 'unsigned char*'} and 'int')
847 | if (backData && (backLen > 0)) {
| ~~~~~~~~^~~

exit status 1

Compilation error: exit status 1

I did not yet connect the board to the USB port. If I do so, the same error comes. I de- and reinstalled the MFRC522 library but without success.

Affected file(s) or example(s):

• Filename 1
• Filename 2

Steps to reproduce:

1. ---

2. ---

3. ---

Observed Results:

• What happened? This could be a description, log output, screenshot, etc.

Expected Results:

• What did you expect to happen?

Relevant Code:

I reduced my code to a minium:

#include <MFRC522.h>

const int PIN_RFID_SDA =     21;
const int PIN_RFID_RST =     22;

MFRC522 mfrc522(PIN_RFID_SDA, PIN_RFID_RST);

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

Any idea, what could I try further? Thank you very much in advanced for your support!

[Gustavo-daCosta]

Same problem here.

OS version: Windows 11
Arduino IDE version: 2.3.2
MFRC522 Library version: 1.4.11
Arduino device: ESP32-WROOM-32
MFRC522 device: RFID-RC522

[CnczubehoerEu]

Ich changes the following manually in MFRC522Extended.cpp:

Line 824: if (backData && backLen && (*backLen > 0)) {
Line 847: if (backData && backLen && (*backLen > 0)) {

Now it works for me.

However, still I do not understand, what's changed in the last few month...

[Gustavo-daCosta]

Yeah, changed manually the code and now it passes, but my RFID module still doesnt recognize any RFID cards.

Probably an hardware problem

Anyway, thank you.

[CnczubehoerEu]

In my case, I can read everything I want. I guess, in your case it is indeed an second problem somewhere else.

[Jan21021]

Same problem here. Problem is with a NodeMCU Esp 32s. When i use the ESP32 Boardmanager 2.0.17 the problem does not exist. The Problem only exists with the newer ESP32 board packs like 3.0 or 3.0.1.

Hope that helps a little bit to narrow down the problem.. =)

[joveaaron]

I think this is happening because of the new IDF release

[Jeff86]

Hey, I had the same issue, I fixed it modifying with if (backData && (backLen != nullptr)) instead of if (backData && (backLen > 0)) for both occurrences. It works great on ESP32 now and I also tested on ESP8266.

Edit: on "MFRC522Extended.cpp" line 824 and 847

[Gustavo-daCosta]

The pull request #625 solves this issue

But it seems that the repository stoped his development, so no pull request are being approved and merged.

So the alternatives are creating a fork with the updates, or use an existing fork