Passing pointer to a pointer to a struct as a function parameter in C#

Question

How do I pass a pointer to a pointer to a struct as a function parameter in C#?

I am trying to use a function from a DLL which has one of its arguments as a double pointer. For e.g.,

struct mystruct
{
   int a;
   char b;
};

[DllImport("mydll.dll")]
private static extern int func_name(int a, char b, mystruct** c);

I guess the correct way to use a pointer like int *a is ref int a. Is there anything similar for int **a?

Cody Gray · Accepted Answer · 2010-11-23 11:20:57Z

2

The CLR equivalent for a pointer to a pointer is ref IntPtr.

An IntPtr is a pointer to an integer, and when you pass it by ref, it's transferred by reference, making it a pointer to a pointer.

You may also need to use the Marshal.PtrToStructure method to convert the pointer to your structure object.

See the section entitled "Manual marshalling" near the bottom of this article for more information.

answered Nov 23, 2010 at 11:20

Cody Gray♦

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Comments

weismat · Accepted Answer · 2010-11-23 11:19:31Z

0

I would work differently.
Any pointer should be used as

System.IntPtr

and I would then use

Marshal.PtrToStructure

for the actual conversion of the pointer to actual structure. Otherwise I would also consider to copy field by field with offsets, which is sometimes easier to debug.

answered Nov 23, 2010 at 11:19

weismat

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