// C# pointer

unsafe void PointerUse(){

  int i=0;

  var pi=&i;  // 这是ok的

  Console.WriteLine("i={0}",i);

  pi[0] += 1;

  Console.WriteLine("i={0}",i);

  var x1=new object();

  var px1=&x1; // warn:CS8500

  Span<int> x2=[1,2,3];

  var px2=&x2;

  Span<int> x3=*px2;

  Console.WriteLine("px2[0]={0}",(*px2)[0]);

  (*px2)[0]+=100;

  Console.WriteLine("px2[0]={0}",(*px2)[0]);

  fixed(int* p=x2){

    p[0]+=100;

    p[2]+=5;

    // var p2=p+1;//指针+ - 数字还是指针

    // var p2=p+sizeof(int);

    var p2=p+1;

    // Console.WriteLine("p2:{0}",p2);

    *p2+=3;

    nint p3=(nint)p+sizeof(int);

    *(int*)p3-=1;

    ((int*)p3)[0]-=1;

    Console.WriteLine("p2:{0},x2:{1}",*p2,string.Join(",",x2.ToArray()));

  }

  Console.WriteLine("px2 convert to nint value:{0}",(nint)px2);

  Console.WriteLine("px2 convert to nuint value:{0}",(nuint)px2);

  //

  var x4=new int[]{1,2,3};

  int[]* px4=&x4;

  Console.WriteLine("px4[0][0]:{0}",px4[0][0]+=3);

  Console.WriteLine("px4[0][0]:{0}",px4[0][1]+=3);

  Console.WriteLine("px4[0][0]:{0}",px4[0][2]+=3);

  fixed( int* px4_1=&x4[0]){

  Console.WriteLine("px4_1[0]:{0}",px4_1[0]);

  Console.WriteLine("px4_1[1]:{0}",px4_1[1]);

  Console.WriteLine("px4_1[2]:{0}",px4_1[2]);

  }

  Console.WriteLine("*px4[0]:{0}",(*px4)[0]);

  Console.WriteLine("*px4[1]:{0}",(*px4)[1]);

  Console.WriteLine("*px4[2]:{0}",(*px4)[2]);

  Console.WriteLine("x4:{0}",string.Join(",",x4.ToArray()));

  (*px4)[0]+=1;

  Console.WriteLine("x4:{0}",string.Join(",",x4.ToArray()));

}