Pinning an updateble struct before passing to unmanaged code?

Question

I using some old API and need to pass the a pointer of a struct to unmanaged code that runs asynchronous.

In other words, after i passing the struct pointer to the unman

Answer 1

Is unsafe code an option?

// allocate unmanaged memory
Foo* foo = (Foo*)Marshal.AllocHGlobal(sizeof(Foo));

// initialize struct
foo->bar = 0;

// invoke unmanaged function which remembers foo
UnsafeNativeMethods.Bar(foo);
Console.WriteLine(foo->bar);

// update struct
foo->bar = 10;

// invoke unmanaged function which uses remembered foo
UnsafeNativeMethods.Qux();
Console.WriteLine(foo->bar);

// free unmanaged memory
Marshal.FreeHGlobal((IntPtr)foo);

This compiles and doesn't throw an exception, but I don't have an unmanaged function at hand to test if it works.

From MSDN:

When AllocHGlobal calls LocalAlloc, it passes a LMEM_FIXED flag, which causes the allocated memory to be locked in place. Also, the allocated memory is not zero-filled.