Convert unsigned char (hex) to long

Using Arduino Programming Questions
1

I finally got my RFID code working. The output of the card ID is: 00A4EA59. When I convert this from HEX to DEC (in calculator) I get 10807897 which is the code of my card.
But how can I do this conversion in the Arduino code ?
I tried strtol but this gave the obvious error that a const char is expected instead of an unsigned char.
Anybody got an idea ?

The complete code:

unsigned char card[12];                    // Contains the value of the RFID card
unsigned char prevcard[12];                // Contains the value of the previously read card
unsigned char i=0;                         // number of read loops
unsigned int different=0;                  // Check if the card has been read already
unsigned long prevmillis=0;                // Contains time of last use card
unsigned long millisdelay=5000;            // Timeout between use of same card

void setup() {
  Serial.begin(9600);                      // Start Serial interface to computer
  Serial1.begin(9600);                     // Start Serial interface for RFID reader
  Serial.println("Start Cardreader");
  Serial.println("----------------------------------");
}

void loop() {
  if (Serial1.available()>0) {            // Check if a card has been read
    card[i]=Serial1.read();               // Fill the array with the value, 10 times needed
    if ((millis()-prevmillis)>millisdelay || millis()<prevmillis) {    // Check if the delay has been crossed or that millis started from 0 again
      memset(prevcard,0,12);              // Clear the prevcard array
    }
    i++;                                  // add 1 to i
    if (i>=11) {                          // Check if loop has passed 11 times
      i=0;                                // Reset i
      if (memcmp(prevcard,card,12)!=0) {  // Check if the previous read card is different from the current
        different=1;              
      }
      if (different) {                    // If previous card is different
        memmove(prevcard,card,12);        // Copy card array contents to prevcard array
        different=0;                      // Reset different check
        prevmillis=millis();              // Set new last read time
        decode();                         // Do something with the RFID keycode
        Serial.println("----------------------------------");
      }      
      delay(10);                          // Delay to avoid double reading
      Serial1.flush();                    // Clear the serial buffer so we can read a new card
    }
  }
}

void decode() {
  Serial.print("Checksum: ");
  for(int p=0;p<4;p++) {                // Write only the checksum, not the card number
    Serial.print(card[p]);
  }
  Serial.print(", Card ID: ");
  for(int p=3;p<11;p++) {                // Write only the card number, not the checksum, outputs 00A4EA59
    Serial.print(card[p]);
  }
  Serial.println("");
}

EDIT: I'm using the Arduino Mega, that's why there's a Serial1

2

What is the format of the 12 char in unsigned char card[12]; ?

3

The code you posted doesn't contain any calls to strtol().

4

But how can I do this conversion in the Arduino code ?

Why do you want to? If it is to compare that string to the value from another card, use strcmp() (stting compare), instead.

I tried strtol but this gave the obvious error that a const char is expected instead of an unsigned char.

You could store your data in a char array, instead of an unsigned char array. If the characters being sent are 0, 1, ..., 9, A, B, ..., F, the ascii values are all in the range that would fit in a char.