Question

What are the limitations of unsafe code, in C#? For example, can I do virtually arbitrary pointer casts and arithmetic as if I were using C or C++?

Answer 1

Yes. All bets are off when unsafe is in play.

This is the idea behind “unsafe” – that the “safety” of verifiable types is removed, and you can cast from a pointer of one type to a pointer of another type without the runtime keeping you from shooting yourself in the foot, if you so desire – much like C or C++.

Here’s an example of using different pointer types in C#:

fixed (Byte* dstBytes = &currentImage[0])
{
    var dstBuffer = (Int64*)dstBytes;
    const int blockCount = ImageSizeInBytes / sizeof(Int64);

    for (var j = 0; j < blockCount; j++)
    {
        dstBuffer[j] = srcBuffer[j];
    }
}

Note the type of the array is Byte[], but after I get a Byte* I can cast it to Int64* and work with 8 bytes at a time.