When would I need to use the stackalloc keyword in C#?

Question

What functionality does the stackalloc keyword provide? When and Why would I want to use it?

Answer 1

Stackalloc will allocate data on the stack, which can be used to avoid the garbage that would be generated by repeatedly creating and destroying arrays of value types within a method.

public unsafe void DoSomeStuff()
{
    byte* unmanaged = stackalloc byte[100];
    byte[] managed = new byte[100];

    //Do stuff with the arrays

    //When this method exits, the unmanaged array gets immediately destroyed.
    //The managed array no longer has any handles to it, so it will get 
    //cleaned up the next time the garbage collector runs.
    //In the mean-time, it is still consuming memory and adding to the list of crap
    //the garbage collector needs to keep track of. If you're doing XNA dev on the
    //Xbox 360, this can be especially bad.
}