Down casting an array of Int[] into an array of Byte[]

Question

Is there a simple way to downcast an array of integers into an array of bytes?
Essentially, I would like to do the following thing (which does not work as is):

int[] myIntArray = new int[20];
byte[] byteArray = (byte[])myInArray;

The reason for doing this is that in my application myIntArray is actually a byte[], but was declared as an int[]. Meaning that only the least significant byte in myIntArray is of interest.

You know that the int array contains values that will fit in a byte, but the compiler doesn't. You'll have to cast each array element to a byte. — CodeCaster
– CodeCaster, Commented Aug 19, 2019 at 12:26
myIntArray is actually a byte[], but was declared as an int[] - How did you get that to happen? P/Invoke? If so, correct the P/Invoke signature. — Matthew Watson
– Matthew Watson, Commented Aug 19, 2019 at 12:28
I wish I could, but I have to use this crappy 3rd party dll. Interestingly, their Python equivalent does not have this problem. Yes, the array of int[] only contains values between 0 and 255, which is the output from a first method. A second method however requires this output, but as a byte[] instead of the int[], lol — stackMeUp
– stackMeUp, Commented Aug 19, 2019 at 12:29
Can't you correct the P/Invoke signature in your C# code? But wait, if the int array contains values like 0x00000001, 0x00000002, 0x00000003 then it is NOT an array of bytes at all; it really is an array of ints. — Matthew Watson
– Matthew Watson, Commented Aug 19, 2019 at 12:32
Assuming this 3rd party DLL is unmanaged, you must somewhere have a P/Invoke DllImport declaration. What does that look like? However, I'm thinking that what you have really is an array of int values (occupying 4 bytes each, but with only the lsb being non-zero), so you really can't cast it or fix it by changing the DLLImport declaration. — Matthew Watson
– Matthew Watson, Commented Aug 19, 2019 at 12:35

Jamiec · Accepted Answer · 2019-08-19 12:30:58Z

5

You might think this would work:

byte[] myByteArray = myIntArray.Cast<byte>().ToArray();

But it doesnt - see Why Enumerable.Cast raises an InvalidCastException?

You can use Select though to project to a new array.

byte[] myByteArray = myIntArray.Select(i => (byte)i).ToArray();

Live demo: https://rextester.com/KVR50332

answered Aug 19, 2019 at 12:30

Jamiec

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stackMeUp Over a year ago

Thanks, I guess I will have to do just that :-)

Antoine V · Accepted Answer · 2019-08-19 12:28:17Z

3

Try using Linq Select

byte[] byteArray = myIntArray.Select(i=> (byte)i).ToArray();

answered Aug 19, 2019 at 12:28

Antoine V

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