How to use unsafe context in Unity

Question

I want to use c++ code in c# for Unity using CLR.

The program works properly outside of unity, but inside of engine it gives me an error:
"cs0227: unsafe code requires the 'unsafe' command line option to be specified"

I am really confused, because the project builds successfully in visual studio (without any errors or warnings). I have "allow unsafe" button activated.

using UnityEngine;
using System.Collections;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

public class newspawn_real : MonoBehaviour {
    void Start () {
        unsafe
        {
            fixed (int * p = &bam[0, 0, 0])
            {
                CppWrapper.CppWrapperClass controlCpp = new CppWrapper.CppWrapperClass();
                controlCpp.allocate_both();
                controlCpp.fill_both();
                controlCpp.fill_wrapper();
            }
        }
    }
    // ...
}

Answer 1

update: on unity 2019 and forward, we don't have the 2.0 subset. use 2.0 Standard.

and although mcs.rsp works, there is a warning noting that mcs is obsolete, and we should use csc.rsp instead.

but it actually works !

Answer 2

You have to explicitly enable unsafe code in Unity. You can follow the steps below:

1. First step, Change Api Compatibility Level to .NET 2.0 Subset.

2. Create a file in your <Project Path>/Assets directory and name it smcs.rsp then put -unsafe inside that file. Save and close that file.

• Close and reopen Visual Studio and Unity Editor.
• You must restart both of them.

It's worth noting that even after doing this and restarting both Unity and Visual Studio, if the problem is still there,

• Rename the smcs.rsp file to csc.rsp, gmcs.rsp or mcs.rsp

Restart Unity Editor and Visual Studio each time until you get one that works. For more details about the file name to use, refer to Platform Dependent Compilation documentation.

Simple C# unsafe code that compiles after this.

public class newspawn_real : MonoBehaviour
{
    unsafe static void SquarePtrParam(int* p)
    {
        *p *= *p;
    }

    void Start()
    {
        unsafe
        {
            int i = 5;
            // Unsafe method: uses address-of operator (&):
            SquarePtrParam(&i);
            Debug.Log(i);
        }
    }
}