Writing a value to a byte array without using C# unsafe nor fixed keyword

Question

In C or C++, we can write the value of a variable directly onto a byte array.

int value = 3;
unsigned char array[100];
*(int*)(&array[10]) = value;

In C#, we also can do this by using unsafe and fixed keyword.

int value = 3;
byte[] array = new byte[100];
fixed(...) { ... }

However, Unity3D does not allow using unsafe nor fixed. In this case, what is the runtime cost-efficient way of doing it? I roughly guess it can be done with using a binary reader or writer class in .Net Core or .Net Framework, but I am not sure of it.

char array is not a byte array. Waht do you want to get? — Backs
– Backs, Commented Mar 23, 2018 at 5:57
You mean specifically how to write int in char array, or in general? — Evk
– Evk, Commented Mar 23, 2018 at 5:58
@Evk Yes. I want to write int in the middle of char or byte array. — Hyunjik Bae
– Hyunjik Bae, Commented Mar 23, 2018 at 6:04
Unity supports unsafe and fixed keywords. See Djeurissen's answer — PassetCronUs
– PassetCronUs, Commented Mar 23, 2018 at 21:20

Evk · Accepted Answer · 2018-03-23 06:16:46Z

2

Since you can't use unsafe - you can just pack that int value yourself:

int value = 3;
var array = new char[100];
array[10] = (char)value; // right half
array[11] = (char)(value >> 16); // left half

Because char is basically ushort in C# (16-bit number). This should do the same as you would in C++ with

*(int*)(&array[10]) = value;

Another approach is using `BitConverter:

var bytes = BitConverter.GetBytes(value);
array[10] = (char)BitConverter.ToInt16(bytes, 0);
array[11] = (char)BitConverter.ToInt16(bytes, 2);

But pay attention to endianess.

answered Mar 23, 2018 at 6:16

Evk

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Djeurissen · Accepted Answer · 2018-03-23 08:01:57Z

2

You could also try to activate the unsafe keyword in Unity: How to use unsafe code Unity

That would spare you the effor to use any "hacks".

answered Mar 23, 2018 at 8:01

Djeurissen

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