C# - Convert unsafe byte* to byte[]

Question

I have an unsafe byte* pointing to a native byte array of known length. How can I convert it to byte[]?

An unsafe sbyte* pointing to a zero-terminated native string can be converted to a C# string easily, because there is a conversion constructor for this purpose, but I can't find a simple way to convert byte* to byte[].

shouldn'y byte[] be const byte* by default? so try indexing the pointer as *(myByte+index); But i guess it if were that easy you wouldn't be asking.... — Shark
– Shark, Commented Jul 10, 2013 at 11:27
You should be able to write *(myByte+index) as myByte[index]. No conversion necessary. — Henk Holterman
– Henk Holterman, Commented Jul 10, 2013 at 11:29
@HenkHolterman I must convert it to byte[] because I have to pass it to the constructor of IPAddress. — kol
– kol, Commented Jul 10, 2013 at 11:33
@HenkHolterman The IPAddress ctor needs a safe/managed byte[]: msdn.microsoft.com/en-us/library/t4k07yby.aspx — kol
– kol, Commented Jul 10, 2013 at 11:37

David Heffernan · Accepted Answer · 2013-07-10 11:31:46Z

25

If ptr is your unsafe pointer, and the array has length len, you can use Marshal.Copy like this:

byte[] arr = new byte[len];
Marshal.Copy((IntPtr)ptr, arr, 0, len);

But I do wonder how you came by an unsafe pointer to native memory. Do you really need unsafe here, or can you solve the problem by using IntPtr instead of an unsafe pointer? And if so then there's probably no need for unsafe code at all.

answered Jul 10, 2013 at 11:31

David Heffernan

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10 Comments

Shark Over a year ago

This looks good, I was gonna suggest traversing the pointed-to array and filling by hand, or memcpy, but this seems like a C# way of doing it. (y)

kol Over a year ago

This question is a follow-up to this one: stackoverflow.com/questions/17549123/…

David Heffernan Over a year ago

I'd err towards IntPtr and Marshal.Copy if I were you.

kol Over a year ago

Thank you, David, I didn't know that an unsafe pointer can be casted to IntPtr.

kol Over a year ago

"I'd err towards IntPtr and Marshal.Copy if I were you." - Why? I would also like to know your opinion on my other question (pls. check out the link if you have time). I haven't got any answers to that one, just some comments.

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dotixx · Accepted Answer · 2013-07-10 11:32:33Z

1

The Marshal class could help you.

byte[] bytes = new byte[length];
for(int i = 0; i < length; ++i)
  bytes[i] = Marshal.ReadByte(yourPtr, i);

I think you might use Marshal.Copy too.

answered Jul 10, 2013 at 11:32

dotixx

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1 Comment

David Heffernan Over a year ago

Since this has to happen in an unsafe block, you don't need Marshal.ReadByte and you can just use good old fashioned pointer de-reference and pointer increment. That is if you wish to perform the copy in a loop rather than using Marshal.Copy.

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