integer to byte array

Forum 2005-2010 (read only) Software Syntax & Programs
1

I'm trying to convert an integer into a byte array and back again.
The maximum value of my integer need only be 255,255 (2 bytes).

I really appreciate the help.

2

If you're just going to use the bytes in an int I would do:

byte low = e;
byte high = e >> 8;

But I think a

typedef struct twobytes {
  byte low;
  byte high;
} uint2x8;

uint82x8 myTwoBytes = { 10 , 255 };

myTwoBytes.low = 60;
myTwoBytes.high = 24;

or

byte myTwoBytes[2] = { 10 , 255 };

myTwoBytes[0] = 60;
myTwoBytes[1] = 24;

solution will be more intuitive to program.

3

Ah, I wasn't clear. I'm not trying to send two different integers each as a separate byte, but one big integer as separate bytes.

If i was sending a number from 0 to 255 it would be easy, I would just send 0x00 - 0xFF, but what if I want to send a number longer than one byte, say 23,582?

How would I convert 23,582 into bytes that I could send one at a time.

On the receiving end how could I turn these bytes back into an integer?

I hope I'm making sense.

Thanks

4

Arduino now has functions to do that for you.

word(high, low);
returns the integer value of the high and low bytes

highByte(int);
lowByte(int);
return the high and low bytes from an integer

The following is an example of how these are used:

byte myTwoBytes[2] = { 10 , 255 };

  int val = word( myTwoBytes[0], myTwoBytes[1]);
  Serial.println(val);
  Serial.print( highByte(val));
  Serial.print( ",");
  Serial.println(lowByte(val));

How best to send the data depends on what is receiving it, you may want to say what that is.

5

I'm really trying to understand. Here is a simplified version of what I'm trying to do.

int myDelay = 23000  // this is for milliseconds

/* this is a packet sent over the UART (Zigbee)
see the 0x??, 0x?? .. those are the bytes i have reserved in the packet to send my integer.*/
int packet[]={0x7E,0x00,0x06,0x00,0x00,0xFF,0x00,0x??,0x??,0x4D};

I'm still at a loss of how to turn 23000 into two bytes (Hex).
My apologies if I'm n00bing it up, I'm pretty new to this stuff.

6

I'm still at a loss of how to turn 23000 into two bytes (Hex).

does the following do what you want?

Serial.print( highByte(23000),HEX);
Serial.print(lowByte(23000),HEX);

Not sure what you want to do with the packet array, perhaps you can clarify.

7

I'm trying to convert a human friendly value into series of bytes to be sent as a serial command packet.

will this work? ..where i have high and low in my byte array? ...

int myDelay = 23000  // this is for milliseconds
byte high = highByte(myDelay);
byte low = lowByte(myDelay);

int packet[]={0x7E,0x00,0x06,0x00,0x00,0xFF,0x00,high,low,0x4D};

Do I have to format the high and low bytes into Hex values .. like the rest of the data in the packet?

8

You don't need to convert them into hex, that should work.

packet is an array of bytes so you save some ram if you do the following:

byte packet[]={0x7E,0x00,0x06,0x00,0x00,0xFF,0x00,high,low,0x4D};

9

Thanks! Its clear now & my code is working :).