问在Arduino错误上将4个字节转换为long

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Here is another way to create 4 bytes to Long value and the reverse. Includes a simple test for these functions.

byte dataj[4];  //4 byte array output
unsigned long testint;
unsigned long testnum, temp;
unsigned long prev_time, cur_time = 0;

void setup() {
  Serial.begin(115200);

  Serial.println(F("********** Initalized +++++++"));
  //   -----4294967295  Max value
  testnum = 4294967295L;  //Start at maximum value

  for (int i = 0; i < 999; i++)
  {
    Serial.print(F("Test #"));
    Serial.print( i + 1);

    Serial.print(F("  Initial value = "));
    Serial.println(testnum);

    prev_time = micros();
    Long_2_Four_Bytes(testnum);


    testint = Four_Bytes_2_Long(dataj[3], dataj[2], dataj[1], dataj[0]);
    cur_time = micros();

    Serial.print(F("         final value   = "));
    Serial.print(testint);
    Serial.print("  time (microsec) = ");  Serial.print(prev_time - cur_time);

    if (testint == testnum)
      Serial.println();
    else
      Serial.println(F("  ERROR  <-----"));

    testnum--;

    delay(50);
  }
}

void loop() {}

//---- Long_2_Four_Bytes ---------------------------
// Fills an array 'dataj[]' with 4 bytes representing
// the 'unsigned long val'.
// Input : unsigned long number - range 0 - 4294967295
// Output : dataj[] where dataj[0] = LSB  & dataj[3] = MSB
//---------------------------------------------------
void Long_2_Four_Bytes(unsigned long val )
{
  unsigned long temp;
  byte data1[] = { 0, 0, 0, 0}; //4 byte array

  temp = val;

  for (byte bytegroup = 0; bytegroup  < 4; bytegroup ++)
  {
    int offset = bytegroup * 8;

    for (byte bit_pntr = 0; bit_pntr < 8; bit_pntr++)
    {
      if ( bitRead(temp, (7 - bit_pntr) + offset) == 1)
        bitSet(data1[bytegroup], (7 - bit_pntr));
    }
  }

  for (byte i = 0; i < 4; i++)
    dataj[i] = data1[i];

}


//-- Four_Bytes_2_Long -------------------------------------
// Creates an unsigned long from  4 bytes where A = MSB and
// D = LSB.  Based upon code by Mehrdad Nazmdar.
// Called by :
// Calls : N/A
// Returns :  unsigned long number - range 0 - 4294967295
//------------------------------------------------------------
unsigned long Four_Bytes_2_Long(byte A, byte B, byte C, byte D)
{
  uint8_t data[4];
  unsigned long testBigint;

  data[0] = D;  //LSB
  data[1] = C;
  data[2] = B;
  data[3] = A; //MSB

  testBigint = *(unsigned long*)(&data);

  return testBigint;
}