custom linear memory allocator

alloc.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace Allocators
{
    class Program
    {
        static unsafe void Main(string[] args)
        {
            LinearAllocator alloc = new LinearAllocator();
            Test* ptr = (Test*)alloc.Allocate(sizeof(Test));
            (*ptr).id = 0;
            (*ptr).age = 33;
            var name = "test".ToArray();
            for (int i = 0; i < name.Length; i++)
            {
                (*ptr).name[i] = name[i];
            }

            alloc.DeallocateAll();
            Test* ptr2 = (Test*)alloc.Allocate(sizeof(Test));
            
            for (int i = 0; i < 4; i++)
            {
                Console.Write((*ptr2).name[i]);    
            }

            alloc.DeallocateAll();
            alloc.Clear();
            Test* ptr3 = (Test*)alloc.Allocate(sizeof(Test));

            for (int i = 0; i < 4; i++)
            {
                Console.Write((*ptr3).name[i]);
            }
            Console.ReadKey();
        }
    }

    unsafe struct Test
    {
        public int id;
        public fixed char name[20];
        public int age;
    }

    unsafe struct LinearAllocator
    {
        const int max_size = 1000000;
        fixed byte buffer[max_size];
        long _offset;
        
        public byte* Allocate(long size)
        {
            var newOffset = _offset + size;
            if (newOffset < max_size)
            {
                fixed (byte* ptr = buffer)
                {
                    byte* res = ptr + _offset;
                    _offset = newOffset;
                    return res;
                }
            }
            return null; 
        }

        public void DeallocateAll()
        {
            _offset = 0;
        }

        public void Clear()
        {
            fixed (byte* ptr = buffer)
            {
                for (int i = 0; i < max_size; i++)
                {
                    ptr[i] = 0;
                }
            }
        }

    }
}