Work with PCZZWSTR

[sensslen]

I'm currently struggling on how to interact with PCZZWSTR. PCZZWSTR has a constructor that takes a char*. How can I convert one or more strings to this structure?

[AArnott]

The simplest way to demonstrate is this:

unsafe
{
    string message = "message1\0message2\0\0";
    fixed (char* pMessage = message)
    {
        PCZZWSTR wstr = new(pMessage);
    }
}

Note that this doesn't copy the memory, it merely points to it. So the wstr I initialize here is only valid while you're inside the fixed block.

If you want to use it longer term, you can allocate native memory:

using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using Windows.Win32.Foundation;

string[] strings = ["message1", "message2"];
PCZZWSTR list = CreateStringList(strings);
try
{
    // use it here.
}
finally
{
    FreeStringList(ref list);
}

// Allocates native memory and copies an array of strings into it.
static unsafe PCZZWSTR CreateStringList(string[] values)
{
    // The length of the buffer is the sum of the individual string lengths, plus their null terminators, plus one more null terminator.
    int charLength = values.Sum(v => v.Length + 1) + 1;
    int byteLength = charLength * sizeof(char);

    char* p = (char*)Marshal.AllocHGlobal(byteLength);
    Span<char> remainingSpan = new(p, charLength);

    foreach (string value in values)
    {
        value.AsSpan().CopyTo(remainingSpan);
        remainingSpan[value.Length] = '\0';
        remainingSpan = remainingSpan.Slice(value.Length + 1);
    }

    remainingSpan[0] = '\0';
    Debug.Assert(remainingSpan.Length == 1);
    return new PCZZWSTR(p);
}

static unsafe void FreeStringList(ref PCZZWSTR list)
{
    Marshal.FreeHGlobal((IntPtr)list.Value);
    list = default;
}

[sensslen]

Thanks a lot for the in detail explanation here.

Now I'm wondering if it may make sense to provide an additional layer of abstraction for methods that use PCZZWSTR to make it easier for c# devs not too familiar with marshalling to use these methods.