C# Convert object to unsafe void*

Question

I'm trying to convert an object to an unsafe void*. Here's an example :

public static void glBufferData(uint target, ulong size, object data, uint usage)
{
    _glBufferData(target, size, data, usage);
}

Here are the parameters of _glBufferData :

uint target, ulong size, void* data, uint usage

I'm passing this object :

float[] positions =
{
    -0.5f, -0.5f,
    0.0f, 0.5f,
    0.5f, -0.5f
};

I tried this but it didn't work.

fixed (void* ptr = &data)
{
}

My class is unsafe by the way.
How can I do that ?

I don't know if it's a dupe necessarily, but maybe [this question](https://stackoverflow.com/questions/15527985/what-is-void-in-c) will help? — Broots Waymb, Apr 27 '21 at 17:20

Michael Liu · Accepted Answer · 2021-04-27T17:36:34.970

0

You cannot take the address of a variable of type object.

Change the type of the data parameter from object to float[] and use fixed to obtain the address of the first array element:

private static extern void _glBufferData(uint target, ulong size, void* data, uint usage);

public static void glBufferData(uint target, ulong size, float[] data, uint usage)
{
    fixed (float* ptr = &data[0])
    {
        _glBufferData(target, size, ptr, usage);
    }
}

You can also try changing void* to float[] in the signature of the _glBufferData method, which would eliminate the need to use fixed:

private static extern void _glBufferData(uint target, ulong size, float[] data, uint usage);

public static void glBufferData(uint target, ulong size, float[] data, uint usage)
{
    _glBufferData(target, size, ptr, usage);
}

edited Apr 27 '21 at 17:36

answered Apr 27 '21 at 17:31

Michael Liu

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It's working, thank you. The downside is that I have to precise the type of the variable. Is there no other way do to that ? – droyer Apr 27 '21 at 19:20
With the first solution I posted, you can create additional overloads of `glBufferData` for each data type you need. All of them can call `_glBufferData`. – Michael Liu Apr 27 '21 at 19:26
This is what I'm gonna do. Thank you. – droyer Apr 27 '21 at 19:29

score 0 · Answer 2 · answered Apr 27 '21 at 18:17

Create a GCHandle for your object

IntPtr handle = (IntPtr) GCHandle.Alloc(this)

Parse your handle as void*

glBufferData(target, size, (void*)handle, usage)

Restore your object from the InPtr GCHandle

public static void glBufferData(uint target, ulong size, void* data, uint usage)
{
            GCHandle myObjectHandle = (GCHandle)((IntPtr)data);
            MyObject obj = (MyObject)myObjectHandle.Target;
}

C# Convert object to unsafe void*

2 Answers2