Strange Errors when using define on an array

Projects Programming
1

I've been trying to set up a program to read UIDs from an RFID card/key chain and I get errors that aren't present in some of the examples.

My code:
#include <MFRC522.h>
#include <SPI.h>

#define RST_PIN 5
#define SS_PIN 53
#define LED_PIN 47

MFRC522 mfrc522(SS_PIN, RST_PIN);

#define CARD_UID {0xFF, 0xFF, 0xFF, 0xFF}
#define FOB_UID {0xFF, 0xFF, 0xFF, 0xFF}

MFRC522::MIFARE_Key key;

void setup()
{
pinMode(LED_PIN, OUTPUT);
Serial.begin(9600);
while(!Serial);
SPI.begin();
mfrc522.PCD_Init();
delay(4);
mfrc522.PCD_DumpVersionToSerial();
Serial.println(F("Scan RFID card"));
}

void loop()
{
if (! mfrc522.PICC_IsNewCardPresent())
{
return;
}
if (! mfrc522.PICC_ReadCardSerial())
{
return;
}
if (mfrc522.uid == CARD_UID)
{
Serial.println("RFID Card detected");
delay(3000);
}
if (mfrc522.uid == FOB_UID)
{
Serial.println("RFID fob detected");
delay(3000);
}
}

Example code:
/*

  • Example to change UID of changeable MIFARE card.
  • This is a MFRC522 library example; for further details and other examples see: GitHub - miguelbalboa/rfid: Arduino RFID Library for MFRC522
  • This sample shows how to set the UID on a UID changeable MIFARE card.
  • @author Tom Clement
  • @license Released into the public domain.
  • Typical pin layout used:
  •         MFRC522      Arduino       Arduino   Arduino    Arduino          Arduino

  •         Reader/PCD   Uno/101       Mega      Nano v3    Leonardo/Micro   Pro Micro
  • Signal Pin Pin Pin Pin Pin Pin
  • RST/Reset RST 9 5 D9 RESET/ICSP-5 RST
  • SPI SS SDA(SS) 10 53 D10 10 10
  • SPI MOSI MOSI 11 / ICSP-4 51 D11 ICSP-4 16
  • SPI MISO MISO 12 / ICSP-1 50 D12 ICSP-1 14
  • SPI SCK SCK 13 / ICSP-3 52 D13 ICSP-3 15
  • More pin layouts for other boards can be found here: GitHub - miguelbalboa/rfid: Arduino RFID Library for MFRC522
    */

#include <SPI.h>
#include <MFRC522.h>

#define RST_PIN 9 // Configurable, see typical pin layout above
#define SS_PIN 10 // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN); // Create MFRC522 instance

/* Set your new UID here! */
#define NEW_UID {0xFF, 0xFF, 0xFF, 0xFF}

MFRC522::MIFARE_Key key;

void setup() {
Serial.begin(9600); // Initialize serial communications with the PC
while (!Serial); // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
SPI.begin(); // Init SPI bus
mfrc522.PCD_Init(); // Init MFRC522 card
Serial.println(F("Warning: this example overwrites the UID of your UID changeable card, use with care!"));

// Prepare key - all keys are set to FFFFFFFFFFFFh at chip delivery from the factory.
for (byte i = 0; i < 6; i++) {
key.keyByte[i] = 0xFF;
}
}

// Setting the UID can be as simple as this:
//void loop() {
// byte newUid[] = NEW_UID;
// if ( mfrc522.MIFARE_SetUid(newUid, (byte)4, true) ) {
// Serial.println("Wrote new UID to card.");
// }
// delay(1000);
//}

// But of course this is a more proper approach
void loop() {

// Reset the loop if no new card present on the sensor/reader. This saves the entire process when idle. And if present, select one.
if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ) {
delay(50);
return;
}

// Now a card is selected. The UID and SAK is in mfrc522.uid.

// Dump UID
Serial.print(F("Card UID:"));
for (byte i = 0; i < mfrc522.uid.size; i++) {
Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
Serial.print(mfrc522.uid.uidByte[i], HEX);
}
Serial.println();

// Dump PICC type
// MFRC522::PICC_Type piccType = mfrc522.PICC_GetType(mfrc522.uid.sak);
// Serial.print(F("PICC type: "));
// Serial.print(mfrc522.PICC_GetTypeName(piccType));
// Serial.print(F(" (SAK "));
// Serial.print(mfrc522.uid.sak);
// Serial.print(")\r\n");
// if ( piccType != MFRC522::PICC_TYPE_MIFARE_MINI
// && piccType != MFRC522::PICC_TYPE_MIFARE_1K
// && piccType != MFRC522::PICC_TYPE_MIFARE_4K) {
// Serial.println(F("This sample only works with MIFARE Classic cards."));
// return;
// }

// Set new UID
byte newUid[] = NEW_UID;
if ( mfrc522.MIFARE_SetUid(newUid, (byte)4, true) ) {
Serial.println(F("Wrote new UID to card."));
}

// Halt PICC and re-select it so DumpToSerial doesn't get confused
mfrc522.PICC_HaltA();
if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ) {
return;
}

// Dump the new memory contents
Serial.println(F("New UID and contents:"));
mfrc522.PICC_DumpToSerial(&(mfrc522.uid));

delay(2000);
}

Output:
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino: In function 'void loop()':
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:10:18: error: expected primary-expression before '{' token
#define CARD_UID {0xD3, 0x37, 0xED, 0x2E}
^
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:37:22: note: in expansion of macro 'CARD_UID'
if (mfrc522.uid == CARD_UID)
^~~~~~~~
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:10:18: error: expected ')' before '{' token
#define CARD_UID {0xD3, 0x37, 0xED, 0x2E}
^
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:37:22: note: in expansion of macro 'CARD_UID'
if (mfrc522.uid == CARD_UID)
^~~~~~~~
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:11:17: error: expected primary-expression before '{' token
#define FOB_UID {0x13, 0x54, 0x0C, 0xB7}
^
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:42:22: note: in expansion of macro 'FOB_UID'
if (mfrc522.uid == FOB_UID)
^~~~~~~
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:11:17: error: expected ')' before '{' token
#define FOB_UID {0x13, 0x54, 0x0C, 0xB7}
^
C:\Users\Richardson Family\Documents\Arduino\RFID_test\RFID_test.ino:42:22: note: in expansion of macro 'FOB_UID'
if (mfrc522.uid == FOB_UID)
^~~~~~~

exit status 1

Compilation error: expected primary-expression before '{' token

2

Where is this line in the code you posted? I don't see it.

3

#define is a macro definition. It maps an identifier to a text value. The macro preprocessor does a simple text substitution. An array definition is invalid for a value so you get an error.

1 Like
4

The definition is valid, it's the use that isn't. Because you can't use assignment with an array.

5

Missed that, the error was on the compare attempt after the macro substitution.

1 Like
6

LOL my turn, compare as well as assignment.

7

that's just the UID on one of the RFID cards I have but for some reason, it's whats causing the error and I forgot to change the logs so they wouldn't have the UID

8

I can see that it's the UID. Two different people have just told you what is causing the error.

What "logs" are you referring to?

9

the "logs" I'm referring to are the error output. I'm not quite sure by what you mean that the use is invalid. are you saying that I can't compare an array with another array?

10

You can compare them algorithmically, but not with the '==' or other comparison operators. Similarly, you can't assign them with '=', except during initialization with constant values.

11

Quite simply as was explained

if (mfrc522.uid == CARD_UID)

is converted into

if (mfrc522.uid == {0xD3, 0x37, 0xED, 0x2E})

by the pre-processor, and that is not a valid statement.
Only if you assign it to a variable while declaring that variable, can you use that macro like that.
but even assigning it while declaring it, you still can not be comparing it with '==' since then you would be comparing the pointers to the 'arrays' and not the array itself. Hence the existance of functions like strcmp() memcmp() etc.

12

this is a valid statement

byte newUid[] = NEW_UID;

and you can use memcmp to compare newUid to mfrc522.uid (comparing 4 bytes from both starting addresses.)

13

I'm getting newUid was not declared in this scope

14

because some parts of that are commented out. I am not going to correct every line of the code (which btw you should post within </> code-tags) just explain to you why something is not a valid statement. for the rest you can contact the author of the code.

15

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