RtlUnicodeToMultiByteSize

// ntdll.dll
#include <windows.h>

NTSTATUS RtlUnicodeToMultiByteSize(
    DWORD* BytesInMultiByteString,
    LPWSTR UnicodeString,
    DWORD BytesInUnicodeString
);

<DllImport("ntdll.dll", ExactSpelling:=True)>
Public Shared Function RtlUnicodeToMultiByteSize(
    <Out> ByRef BytesInMultiByteString As UInteger,   ' DWORD* out
    <MarshalAs(UnmanagedType.LPWStr)> UnicodeString As String,   ' LPWSTR
    BytesInUnicodeString As UInteger   ' DWORD
) As Integer
End Function

' BytesInMultiByteString : DWORD* out
' UnicodeString : LPWSTR
' BytesInUnicodeString : DWORD
Declare PtrSafe Function RtlUnicodeToMultiByteSize Lib "ntdll" ( _
    ByRef BytesInMultiByteString As Long, _
    ByVal UnicodeString As LongPtr, _
    ByVal BytesInUnicodeString As Long) As Long
' VBA7前提(PtrSafe)。32bit Office では LongPtr→Long。Integer=16bit / Long=32bit / LongLong=64bit。

import ctypes
from ctypes import wintypes

RtlUnicodeToMultiByteSize = ctypes.windll.ntdll.RtlUnicodeToMultiByteSize
RtlUnicodeToMultiByteSize.restype = ctypes.c_int
RtlUnicodeToMultiByteSize.argtypes = [
    ctypes.POINTER(wintypes.DWORD),  # BytesInMultiByteString : DWORD* out
    wintypes.LPCWSTR,  # UnicodeString : LPWSTR
    wintypes.DWORD,  # BytesInUnicodeString : DWORD
]

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('ntdll.dll')
RtlUnicodeToMultiByteSize = Fiddle::Function.new(
  lib['RtlUnicodeToMultiByteSize'],
  [
    Fiddle::TYPE_VOIDP,  # BytesInMultiByteString : DWORD* out
    Fiddle::TYPE_VOIDP,  # UnicodeString : LPWSTR
    -Fiddle::TYPE_INT,  # BytesInUnicodeString : DWORD
  ],
  Fiddle::TYPE_INT)

#[link(name = "ntdll")]
extern "system" {
    fn RtlUnicodeToMultiByteSize(
        BytesInMultiByteString: *mut u32,  // DWORD* out
        UnicodeString: *mut u16,  // LPWSTR
        BytesInUnicodeString: u32  // DWORD
    ) -> i32;
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[DllImport("ntdll.dll")]
public static extern int RtlUnicodeToMultiByteSize(out uint BytesInMultiByteString, [MarshalAs(UnmanagedType.LPWStr)] string UnicodeString, uint BytesInUnicodeString);
"@
$api = Add-Type -MemberDefinition $sig -Name 'ntdll_RtlUnicodeToMultiByteSize' -Namespace Win32 -PassThru
# $api::RtlUnicodeToMultiByteSize(BytesInMultiByteString, UnicodeString, BytesInUnicodeString)

#uselib "ntdll.dll"
#func global RtlUnicodeToMultiByteSize "RtlUnicodeToMultiByteSize" sptr, sptr, sptr
; RtlUnicodeToMultiByteSize varptr(BytesInMultiByteString), UnicodeString, BytesInUnicodeString   ; 戻り値は stat
; BytesInMultiByteString : DWORD* out -> "sptr"
; UnicodeString : LPWSTR -> "sptr"
; BytesInUnicodeString : DWORD -> "sptr"
; ※HSP3.7は #func のため戻り値はシステム変数 stat に格納されます。

#uselib "ntdll.dll"
#cfunc global RtlUnicodeToMultiByteSize "RtlUnicodeToMultiByteSize" var, wstr, int
; res = RtlUnicodeToMultiByteSize(BytesInMultiByteString, UnicodeString, BytesInUnicodeString)
; BytesInMultiByteString : DWORD* out -> "var"
; UnicodeString : LPWSTR -> "wstr"
; BytesInUnicodeString : DWORD -> "int"
; ※出力/バッファ引数は var 方式(変数を直接渡す)。varptr 方式にも切替可。

; NTSTATUS RtlUnicodeToMultiByteSize(DWORD* BytesInMultiByteString, LPWSTR UnicodeString, DWORD BytesInUnicodeString)
#uselib "ntdll.dll"
#cfunc global RtlUnicodeToMultiByteSize "RtlUnicodeToMultiByteSize" var, wstr, int
; res = RtlUnicodeToMultiByteSize(BytesInMultiByteString, UnicodeString, BytesInUnicodeString)
; BytesInMultiByteString : DWORD* out -> "var"
; UnicodeString : LPWSTR -> "wstr"
; BytesInUnicodeString : DWORD -> "int"
; ※出力/バッファ引数は var 方式(変数を直接渡す)。varptr 方式にも切替可。

import (
	"golang.org/x/sys/windows"
	"unsafe"
)

var (
	ntdll = windows.NewLazySystemDLL("ntdll.dll")
	procRtlUnicodeToMultiByteSize = ntdll.NewProc("RtlUnicodeToMultiByteSize")
)

// BytesInMultiByteString (DWORD* out), UnicodeString (LPWSTR), BytesInUnicodeString (DWORD)
r1, _, err := procRtlUnicodeToMultiByteSize.Call(
	uintptr(BytesInMultiByteString),
	uintptr(unsafe.Pointer(windows.StringToUTF16Ptr(UnicodeString))),
	uintptr(BytesInUnicodeString),
)
_ = err  // syscall.Errno (valid when the call sets last-error)
_ = r1   // NTSTATUS

function RtlUnicodeToMultiByteSize(
  BytesInMultiByteString: Pointer;   // DWORD* out
  UnicodeString: PWideChar;   // LPWSTR
  BytesInUnicodeString: DWORD   // DWORD
): Integer; stdcall;
  external 'ntdll.dll' name 'RtlUnicodeToMultiByteSize';

result := DllCall("ntdll\RtlUnicodeToMultiByteSize"
    , "Ptr", BytesInMultiByteString   ; DWORD* out
    , "WStr", UnicodeString   ; LPWSTR
    , "UInt", BytesInUnicodeString   ; DWORD
    , "Int")   ; return: NTSTATUS

●RtlUnicodeToMultiByteSize(BytesInMultiByteString, UnicodeString, BytesInUnicodeString) = DLL("ntdll.dll", "int RtlUnicodeToMultiByteSize(void*, char*, dword)")
# 呼び出し: RtlUnicodeToMultiByteSize(BytesInMultiByteString, UnicodeString, BytesInUnicodeString)
# BytesInMultiByteString : DWORD* out -> "void*"
# UnicodeString : LPWSTR -> "char*"
# BytesInUnicodeString : DWORD -> "dword"
# なでしこ1は32bit・ANSI(Shift_JIS)。文字列=char*(ANSI)、ポインタ/ハンドル=void*(4byte)。