DhcpV4GetFreeIPAddress

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

DWORD DhcpV4GetFreeIPAddress(
    LPWSTR ServerIpAddress,   // optional
    DWORD ScopeId,
    DWORD StartIP,
    DWORD EndIP,
    DWORD NumFreeAddrReq,
    DHCP_IP_ARRAY** IPAddrList
);

<DllImport("DHCPSAPI.dll", ExactSpelling:=True)>
Public Shared Function DhcpV4GetFreeIPAddress(
    <MarshalAs(UnmanagedType.LPWStr)> ServerIpAddress As String,   ' LPWSTR optional
    ScopeId As UInteger,   ' DWORD
    StartIP As UInteger,   ' DWORD
    EndIP As UInteger,   ' DWORD
    NumFreeAddrReq As UInteger,   ' DWORD
    IPAddrList As IntPtr   ' DHCP_IP_ARRAY** out
) As UInteger
End Function

' ServerIpAddress : LPWSTR optional
' ScopeId : DWORD
' StartIP : DWORD
' EndIP : DWORD
' NumFreeAddrReq : DWORD
' IPAddrList : DHCP_IP_ARRAY** out
Declare PtrSafe Function DhcpV4GetFreeIPAddress Lib "dhcpsapi" ( _
    ByVal ServerIpAddress As LongPtr, _
    ByVal ScopeId As Long, _
    ByVal StartIP As Long, _
    ByVal EndIP As Long, _
    ByVal NumFreeAddrReq As Long, _
    ByVal IPAddrList As LongPtr) As Long
' VBA7前提(PtrSafe)。32bit Office では LongPtr→Long。Integer=16bit / Long=32bit / LongLong=64bit。

import ctypes
from ctypes import wintypes

DhcpV4GetFreeIPAddress = ctypes.windll.dhcpsapi.DhcpV4GetFreeIPAddress
DhcpV4GetFreeIPAddress.restype = wintypes.DWORD
DhcpV4GetFreeIPAddress.argtypes = [
    wintypes.LPCWSTR,  # ServerIpAddress : LPWSTR optional
    wintypes.DWORD,  # ScopeId : DWORD
    wintypes.DWORD,  # StartIP : DWORD
    wintypes.DWORD,  # EndIP : DWORD
    wintypes.DWORD,  # NumFreeAddrReq : DWORD
    ctypes.c_void_p,  # IPAddrList : DHCP_IP_ARRAY** out
]

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('DHCPSAPI.dll')
DhcpV4GetFreeIPAddress = Fiddle::Function.new(
  lib['DhcpV4GetFreeIPAddress'],
  [
    Fiddle::TYPE_VOIDP,  # ServerIpAddress : LPWSTR optional
    -Fiddle::TYPE_INT,  # ScopeId : DWORD
    -Fiddle::TYPE_INT,  # StartIP : DWORD
    -Fiddle::TYPE_INT,  # EndIP : DWORD
    -Fiddle::TYPE_INT,  # NumFreeAddrReq : DWORD
    Fiddle::TYPE_VOIDP,  # IPAddrList : DHCP_IP_ARRAY** out
  ],
  -Fiddle::TYPE_INT)

#[link(name = "dhcpsapi")]
extern "system" {
    fn DhcpV4GetFreeIPAddress(
        ServerIpAddress: *mut u16,  // LPWSTR optional
        ScopeId: u32,  // DWORD
        StartIP: u32,  // DWORD
        EndIP: u32,  // DWORD
        NumFreeAddrReq: u32,  // DWORD
        IPAddrList: *mut *mut DHCP_IP_ARRAY  // DHCP_IP_ARRAY** out
    ) -> u32;
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[DllImport("DHCPSAPI.dll")]
public static extern uint DhcpV4GetFreeIPAddress([MarshalAs(UnmanagedType.LPWStr)] string ServerIpAddress, uint ScopeId, uint StartIP, uint EndIP, uint NumFreeAddrReq, IntPtr IPAddrList);
"@
$api = Add-Type -MemberDefinition $sig -Name 'DHCPSAPI_DhcpV4GetFreeIPAddress' -Namespace Win32 -PassThru
# $api::DhcpV4GetFreeIPAddress(ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, IPAddrList)

#uselib "DHCPSAPI.dll"
#func global DhcpV4GetFreeIPAddress "DhcpV4GetFreeIPAddress" sptr, sptr, sptr, sptr, sptr, sptr
; DhcpV4GetFreeIPAddress ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, varptr(IPAddrList)   ; 戻り値は stat
; ServerIpAddress : LPWSTR optional -> "sptr"
; ScopeId : DWORD -> "sptr"
; StartIP : DWORD -> "sptr"
; EndIP : DWORD -> "sptr"
; NumFreeAddrReq : DWORD -> "sptr"
; IPAddrList : DHCP_IP_ARRAY** out -> "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 "DHCPSAPI.dll"
#cfunc global DhcpV4GetFreeIPAddress "DhcpV4GetFreeIPAddress" wstr, int, int, int, int, var
; res = DhcpV4GetFreeIPAddress(ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, IPAddrList)
; ServerIpAddress : LPWSTR optional -> "wstr"
; ScopeId : DWORD -> "int"
; StartIP : DWORD -> "int"
; EndIP : DWORD -> "int"
; NumFreeAddrReq : DWORD -> "int"
; IPAddrList : DHCP_IP_ARRAY** out -> "var"
; ※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。

; DWORD DhcpV4GetFreeIPAddress(LPWSTR ServerIpAddress, DWORD ScopeId, DWORD StartIP, DWORD EndIP, DWORD NumFreeAddrReq, DHCP_IP_ARRAY** IPAddrList)
#uselib "DHCPSAPI.dll"
#cfunc global DhcpV4GetFreeIPAddress "DhcpV4GetFreeIPAddress" wstr, int, int, int, int, var
; res = DhcpV4GetFreeIPAddress(ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, IPAddrList)
; ServerIpAddress : LPWSTR optional -> "wstr"
; ScopeId : DWORD -> "int"
; StartIP : DWORD -> "int"
; EndIP : DWORD -> "int"
; NumFreeAddrReq : DWORD -> "int"
; IPAddrList : DHCP_IP_ARRAY** out -> "var"
; ※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 (
	dhcpsapi = windows.NewLazySystemDLL("DHCPSAPI.dll")
	procDhcpV4GetFreeIPAddress = dhcpsapi.NewProc("DhcpV4GetFreeIPAddress")
)

// ServerIpAddress (LPWSTR optional), ScopeId (DWORD), StartIP (DWORD), EndIP (DWORD), NumFreeAddrReq (DWORD), IPAddrList (DHCP_IP_ARRAY** out)
r1, _, err := procDhcpV4GetFreeIPAddress.Call(
	uintptr(unsafe.Pointer(windows.StringToUTF16Ptr(ServerIpAddress))),
	uintptr(ScopeId),
	uintptr(StartIP),
	uintptr(EndIP),
	uintptr(NumFreeAddrReq),
	uintptr(IPAddrList),
)
_ = err  // syscall.Errno (valid when the call sets last-error)
_ = r1   // DWORD

function DhcpV4GetFreeIPAddress(
  ServerIpAddress: PWideChar;   // LPWSTR optional
  ScopeId: DWORD;   // DWORD
  StartIP: DWORD;   // DWORD
  EndIP: DWORD;   // DWORD
  NumFreeAddrReq: DWORD;   // DWORD
  IPAddrList: Pointer   // DHCP_IP_ARRAY** out
): DWORD; stdcall;
  external 'DHCPSAPI.dll' name 'DhcpV4GetFreeIPAddress';

result := DllCall("DHCPSAPI\DhcpV4GetFreeIPAddress"
    , "WStr", ServerIpAddress   ; LPWSTR optional
    , "UInt", ScopeId   ; DWORD
    , "UInt", StartIP   ; DWORD
    , "UInt", EndIP   ; DWORD
    , "UInt", NumFreeAddrReq   ; DWORD
    , "Ptr", IPAddrList   ; DHCP_IP_ARRAY** out
    , "UInt")   ; return: DWORD

●DhcpV4GetFreeIPAddress(ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, IPAddrList) = DLL("DHCPSAPI.dll", "dword DhcpV4GetFreeIPAddress(char*, dword, dword, dword, dword, void*)")
# 呼び出し: DhcpV4GetFreeIPAddress(ServerIpAddress, ScopeId, StartIP, EndIP, NumFreeAddrReq, IPAddrList)
# ServerIpAddress : LPWSTR optional -> "char*"
# ScopeId : DWORD -> "dword"
# StartIP : DWORD -> "dword"
# EndIP : DWORD -> "dword"
# NumFreeAddrReq : DWORD -> "dword"
# IPAddrList : DHCP_IP_ARRAY** out -> "void*"
# 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)。