EngUnicodeToMultiByteN

// GDI32.dll
#include <windows.h>

void EngUnicodeToMultiByteN(
    LPSTR MultiByteString,
    DWORD MaxBytesInMultiByteString,
    DWORD* BytesInMultiByteString,   // optional
    LPWSTR UnicodeString,
    DWORD BytesInUnicodeString
);

<DllImport("GDI32.dll", ExactSpelling:=True)>
Public Shared Sub EngUnicodeToMultiByteN(
    <MarshalAs(UnmanagedType.LPStr)> MultiByteString As System.Text.StringBuilder,   ' LPSTR out
    MaxBytesInMultiByteString As UInteger,   ' DWORD
    BytesInMultiByteString As IntPtr,   ' DWORD* optional, out
    <MarshalAs(UnmanagedType.LPWStr)> UnicodeString As String,   ' LPWSTR
    BytesInUnicodeString As UInteger   ' DWORD
)
End Sub

' MultiByteString : LPSTR out
' MaxBytesInMultiByteString : DWORD
' BytesInMultiByteString : DWORD* optional, out
' UnicodeString : LPWSTR
' BytesInUnicodeString : DWORD
Declare PtrSafe Sub EngUnicodeToMultiByteN Lib "gdi32" ( _
    ByVal MultiByteString As String, _
    ByVal MaxBytesInMultiByteString As Long, _
    ByVal BytesInMultiByteString As LongPtr, _
    ByVal UnicodeString As LongPtr, _
    ByVal BytesInUnicodeString As Long)
' VBA7前提(PtrSafe)。32bit Office では LongPtr→Long。Integer=16bit / Long=32bit / LongLong=64bit。

import ctypes
from ctypes import wintypes

EngUnicodeToMultiByteN = ctypes.windll.gdi32.EngUnicodeToMultiByteN
EngUnicodeToMultiByteN.restype = None
EngUnicodeToMultiByteN.argtypes = [
    wintypes.LPSTR,  # MultiByteString : LPSTR out
    wintypes.DWORD,  # MaxBytesInMultiByteString : DWORD
    ctypes.POINTER(wintypes.DWORD),  # BytesInMultiByteString : DWORD* optional, out
    wintypes.LPCWSTR,  # UnicodeString : LPWSTR
    wintypes.DWORD,  # BytesInUnicodeString : DWORD
]

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('GDI32.dll')
EngUnicodeToMultiByteN = Fiddle::Function.new(
  lib['EngUnicodeToMultiByteN'],
  [
    Fiddle::TYPE_VOIDP,  # MultiByteString : LPSTR out
    -Fiddle::TYPE_INT,  # MaxBytesInMultiByteString : DWORD
    Fiddle::TYPE_VOIDP,  # BytesInMultiByteString : DWORD* optional, out
    Fiddle::TYPE_VOIDP,  # UnicodeString : LPWSTR
    -Fiddle::TYPE_INT,  # BytesInUnicodeString : DWORD
  ],
  Fiddle::TYPE_VOID)

#[link(name = "gdi32")]
extern "system" {
    fn EngUnicodeToMultiByteN(
        MultiByteString: *mut u8,  // LPSTR out
        MaxBytesInMultiByteString: u32,  // DWORD
        BytesInMultiByteString: *mut u32,  // DWORD* optional, out
        UnicodeString: *mut u16,  // LPWSTR
        BytesInUnicodeString: u32  // DWORD
    );
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[DllImport("GDI32.dll")]
public static extern void EngUnicodeToMultiByteN([MarshalAs(UnmanagedType.LPStr)] System.Text.StringBuilder MultiByteString, uint MaxBytesInMultiByteString, IntPtr BytesInMultiByteString, [MarshalAs(UnmanagedType.LPWStr)] string UnicodeString, uint BytesInUnicodeString);
"@
$api = Add-Type -MemberDefinition $sig -Name 'GDI32_EngUnicodeToMultiByteN' -Namespace Win32 -PassThru
# $api::EngUnicodeToMultiByteN(MultiByteString, MaxBytesInMultiByteString, BytesInMultiByteString, UnicodeString, BytesInUnicodeString)

#uselib "GDI32.dll"
#func global EngUnicodeToMultiByteN "EngUnicodeToMultiByteN" sptr, sptr, sptr, sptr, sptr
; EngUnicodeToMultiByteN varptr(MultiByteString), MaxBytesInMultiByteString, varptr(BytesInMultiByteString), UnicodeString, BytesInUnicodeString
; MultiByteString : LPSTR out -> "sptr"
; MaxBytesInMultiByteString : DWORD -> "sptr"
; BytesInMultiByteString : DWORD* optional, out -> "sptr"
; UnicodeString : LPWSTR -> "sptr"
; BytesInUnicodeString : DWORD -> "sptr"

#uselib "GDI32.dll"
#func global EngUnicodeToMultiByteN "EngUnicodeToMultiByteN" var, int, var, wstr, int
; EngUnicodeToMultiByteN MultiByteString, MaxBytesInMultiByteString, BytesInMultiByteString, UnicodeString, BytesInUnicodeString
; MultiByteString : LPSTR out -> "var"
; MaxBytesInMultiByteString : DWORD -> "int"
; BytesInMultiByteString : DWORD* optional, 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。

; void EngUnicodeToMultiByteN(LPSTR MultiByteString, DWORD MaxBytesInMultiByteString, DWORD* BytesInMultiByteString, LPWSTR UnicodeString, DWORD BytesInUnicodeString)
#uselib "GDI32.dll"
#func global EngUnicodeToMultiByteN "EngUnicodeToMultiByteN" var, int, var, wstr, int
; EngUnicodeToMultiByteN MultiByteString, MaxBytesInMultiByteString, BytesInMultiByteString, UnicodeString, BytesInUnicodeString
; MultiByteString : LPSTR out -> "var"
; MaxBytesInMultiByteString : DWORD -> "int"
; BytesInMultiByteString : DWORD* optional, 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 (
	gdi32 = windows.NewLazySystemDLL("GDI32.dll")
	procEngUnicodeToMultiByteN = gdi32.NewProc("EngUnicodeToMultiByteN")
)

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

procedure EngUnicodeToMultiByteN(
  MultiByteString: PAnsiChar;   // LPSTR out
  MaxBytesInMultiByteString: DWORD;   // DWORD
  BytesInMultiByteString: Pointer;   // DWORD* optional, out
  UnicodeString: PWideChar;   // LPWSTR
  BytesInUnicodeString: DWORD   // DWORD
); stdcall;
  external 'GDI32.dll' name 'EngUnicodeToMultiByteN';

result := DllCall("GDI32\EngUnicodeToMultiByteN"
    , "Ptr", MultiByteString   ; LPSTR out
    , "UInt", MaxBytesInMultiByteString   ; DWORD
    , "Ptr", BytesInMultiByteString   ; DWORD* optional, out
    , "WStr", UnicodeString   ; LPWSTR
    , "UInt", BytesInUnicodeString   ; DWORD
    , "Int")   ; return: void

●EngUnicodeToMultiByteN(MultiByteString, MaxBytesInMultiByteString, BytesInMultiByteString, UnicodeString, BytesInUnicodeString) = DLL("GDI32.dll", "int EngUnicodeToMultiByteN(char*, dword, void*, char*, dword)")
# 呼び出し: EngUnicodeToMultiByteN(MultiByteString, MaxBytesInMultiByteString, BytesInMultiByteString, UnicodeString, BytesInUnicodeString)
# MultiByteString : LPSTR out -> "char*"
# MaxBytesInMultiByteString : DWORD -> "dword"
# BytesInMultiByteString : DWORD* optional, 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)。