#include <SD.h>

File file;

void setup() {
  Serial.begin(9600);
  if (!SD.begin()) {
    Serial.println("SD init fail");
    return;
  }

  file = SD.open("file.txt", FILE_WRITE);
  if (!file) {
    Serial.println("Failed to open file");
    return;
  }

  // lets say DLC is 3, so the data array is only 3 bytes
  int dlc = 8;
  int data[] = {0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0};

  char *ptr = (char *) malloc(dlc * 8);
  for (int i = 0; i < dlc; i++) {
    *(ptr + i) = data[i];
  }

  free(ptr);
}

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

}