How to get a string from an inline array in a struct?

[Lightczx]

How can I get the MODULEENTRY32.szModule 's string representation ?
It's currently defined as __winmdroot_Foundation_CHAR_256 struct type.

[AArnott]

If this were using a UTF-16 character array, there would be a ToString() method on the struct that would produce what you want.
But as this is a CHAR inline array, you have to do it yourself. I filed #636 to improve this.

This is how you can do it. It produces the string "abc":

using System.Text;
using Windows.Win32;
using Windows.Win32.Foundation;
using Windows.Win32.System.Diagnostics.ToolHelp;

MODULEENTRY32 m = default;
m.szModule._0 = (CHAR)(byte)'a';
m.szModule._1 = (CHAR)(byte)'b';
m.szModule._2 = (CHAR)(byte)'c';

unsafe
{
    byte* pszModule = (byte*)&m.szModule;
    string szModule = Encoding.UTF8.GetString(pszModule, GetLength(pszModule));
}

static unsafe int GetLength(byte* pszStr)
{
    int len = 0;
    while (*pszStr++ != 0)
    {
        len += 1;
    }

    return len;
}

[Lightczx]

Thanks, It works properly!

[Lightczx]

C# 11 introduced a new feature called UTF-8 string literals.
As it now we can use utf8 string easily, I just wrote a method to get the "string"

public static unsafe ReadOnlySpan<byte> AsNullTerminatedReadOnlySpan(this in __CHAR_256 char256)
{
    fixed (CHAR* pszChar = &char256._0)
    {
        return MemoryMarshal.CreateReadOnlySpanFromNullTerminated((byte*)pszChar);
    }
}

[AArnott]

Why not use AsReadOnlySpan then? That method being in the struct (and defining certain attributes or the new modifier) allows C# to help the caller stay safe, but it looks like your extension method will circumvent C#'s protections.

[AArnott]

If it's just that you want the span sized given null-termination, I imagine we could add that for CHAR-based inline array structs.

[jnm2]

I think it would be possible to create a span to the actual ref instead of to a pointer, where there would be no GC hole, but I don't remember how. I do know that the Span API has new ref constructors for a single item but no count IIRC.

[AArnott]

Yes, it should be possible. And we already do. That's why I wonder why this extension method need exist at all. If it's just so the span length is set till the null terminator instead of the full fixed array's length, that's something we can make easy for CHAR inline array structs just as we do for char ones.

[Lightczx]

It‘s a semantical issue:
I don't want lead to unnecessary memory allocation then:
If I use AsReadOnlySpan, it's a bit hard to compare with certain ReadOnlySpan<byte> like "modulePath.dll"u8
I have to cast the ReadOnlySpan<CHAR> to ReadonlySpan<byte> using MemoryMarshal.AsBytes then use MemoryMarshal.IndexOf to compare between them.
If there is API return null terminated readonly span of byte, I can just directly use MemoryMarshal.SequenceEqual and the code reads more smooth though.

After all, it's just something semantical.