结构内部的c＃2D数组

Question

I need to return a struct from a method. One of the members of the struct needs to be a 2D array. I am aware of using fixed size buffers to declare the size of the array in the struct and of using

[StructLayout(LayoutKind.Explicit)]
public struct struct1
{
    [FieldOffset(0)]
       ....
}

but here is the issue. I cannot do this as I do not know the length of the array ahead of time. The size of the array depends on parameters chosen by the user at runtime.

struct foo {
    int x;
    double[,]  A = new double[N, M];
};

I do not know N or M ahead of time. They are selected by the user at runtime.

Is this possible? If yes, how would one do it? Thank you in advance for any suggestions or advice you may be able to provide.

Answer 1

It is not possible to inline a variable sized array because structs must have fixed size known at compile time. You can of course have a reference to an array of a size only known at runtime.

internal struct Foo
{
   internal Double[,] bar;

   internal Foo(Int32 sizeX, Int32 sizeY)
   {
     this.bar = new Double[sizeX, sizeY];
   }
}

You can use this struct like this

private function Foo InitializeFoo(Int32 sizeX, Int32 sizeY)
{
   var foo = new Foo(sizeX, sizeY);

   for (var y = 0; y < sizeY; y++)
   {
      for (var x = 0; x < sizeX; x++)
      {
         foo.bar[x, y] = x * y;
      }
   }

   return foo;
}

and calling this method like

var foo = InitializeFoo(12, 34);

will give you an instance of Foo with the field bar referencing a Double array of dimension 12 x 34.