GetEnvironmentVariableA

// KERNEL32.dll  (ANSI / -A)
#include <windows.h>

DWORD GetEnvironmentVariableA(
    LPCSTR lpName,   // optional
    LPSTR lpBuffer,   // optional
    DWORD nSize
);

<DllImport("KERNEL32.dll", CharSet:=CharSet.Ansi, SetLastError:=True, ExactSpelling:=True)>
Public Shared Function GetEnvironmentVariableA(
    <MarshalAs(UnmanagedType.LPStr)> lpName As String,   ' LPCSTR optional
    <MarshalAs(UnmanagedType.LPStr)> lpBuffer As System.Text.StringBuilder,   ' LPSTR optional, out
    nSize As UInteger   ' DWORD
) As UInteger
End Function

' lpName : LPCSTR optional
' lpBuffer : LPSTR optional, out
' nSize : DWORD
Declare PtrSafe Function GetEnvironmentVariableA Lib "kernel32" ( _
    ByVal lpName As String, _
    ByVal lpBuffer As String, _
    ByVal nSize 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

GetEnvironmentVariableA = ctypes.windll.kernel32.GetEnvironmentVariableA
GetEnvironmentVariableA.restype = wintypes.DWORD
GetEnvironmentVariableA.argtypes = [
    wintypes.LPCSTR,  # lpName : LPCSTR optional
    wintypes.LPSTR,  # lpBuffer : LPSTR optional, out
    wintypes.DWORD,  # nSize : DWORD
]
# GetLastError: use ctypes.GetLastError() (or ctypes.WinDLL(use_last_error=True))

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('KERNEL32.dll')
GetEnvironmentVariableA = Fiddle::Function.new(
  lib['GetEnvironmentVariableA'],
  [
    Fiddle::TYPE_VOIDP,  # lpName : LPCSTR optional
    Fiddle::TYPE_VOIDP,  # lpBuffer : LPSTR optional, out
    -Fiddle::TYPE_INT,  # nSize : DWORD
  ],
  -Fiddle::TYPE_INT)

#[link(name = "kernel32")]
extern "system" {
    fn GetEnvironmentVariableA(
        lpName: *const u8,  // LPCSTR optional
        lpBuffer: *mut u8,  // LPSTR optional, out
        nSize: u32  // DWORD
    ) -> u32;
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[DllImport("KERNEL32.dll", CharSet = CharSet.Ansi, SetLastError = true)]
public static extern uint GetEnvironmentVariableA([MarshalAs(UnmanagedType.LPStr)] string lpName, [MarshalAs(UnmanagedType.LPStr)] System.Text.StringBuilder lpBuffer, uint nSize);
"@
$api = Add-Type -MemberDefinition $sig -Name 'KERNEL32_GetEnvironmentVariableA' -Namespace Win32 -PassThru
# $api::GetEnvironmentVariableA(lpName, lpBuffer, nSize)

#uselib "KERNEL32.dll"
#func global GetEnvironmentVariableA "GetEnvironmentVariableA" sptr, sptr, sptr
; GetEnvironmentVariableA lpName, varptr(lpBuffer), nSize   ; 戻り値は stat
; lpName : LPCSTR optional -> "sptr"
; lpBuffer : LPSTR optional, out -> "sptr"
; nSize : 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 "KERNEL32.dll"
#cfunc global GetEnvironmentVariableA "GetEnvironmentVariableA" str, var, int
; res = GetEnvironmentVariableA(lpName, lpBuffer, nSize)
; lpName : LPCSTR optional -> "str"
; lpBuffer : LPSTR optional, out -> "var"
; nSize : 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。

; DWORD GetEnvironmentVariableA(LPCSTR lpName, LPSTR lpBuffer, DWORD nSize)
#uselib "KERNEL32.dll"
#cfunc global GetEnvironmentVariableA "GetEnvironmentVariableA" str, var, int
; res = GetEnvironmentVariableA(lpName, lpBuffer, nSize)
; lpName : LPCSTR optional -> "str"
; lpBuffer : LPSTR optional, out -> "var"
; nSize : 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 (
	kernel32 = windows.NewLazySystemDLL("KERNEL32.dll")
	procGetEnvironmentVariableA = kernel32.NewProc("GetEnvironmentVariableA")
)

// lpName (LPCSTR optional), lpBuffer (LPSTR optional, out), nSize (DWORD)
r1, _, err := procGetEnvironmentVariableA.Call(
	uintptr(unsafe.Pointer(windows.BytePtrFromString(lpName))),
	uintptr(lpBuffer),
	uintptr(nSize),
)
_ = err  // syscall.Errno (valid when the call sets last-error)
_ = r1   // DWORD

function GetEnvironmentVariableA(
  lpName: PAnsiChar;   // LPCSTR optional
  lpBuffer: PAnsiChar;   // LPSTR optional, out
  nSize: DWORD   // DWORD
): DWORD; stdcall;
  external 'KERNEL32.dll' name 'GetEnvironmentVariableA';

result := DllCall("KERNEL32\GetEnvironmentVariableA"
    , "AStr", lpName   ; LPCSTR optional
    , "Ptr", lpBuffer   ; LPSTR optional, out
    , "UInt", nSize   ; DWORD
    , "UInt")   ; return: DWORD

●GetEnvironmentVariableA(lpName, lpBuffer, nSize) = DLL("KERNEL32.dll", "dword GetEnvironmentVariableA(char*, char*, dword)")
# 呼び出し: GetEnvironmentVariableA(lpName, lpBuffer, nSize)
# lpName : LPCSTR optional -> "char*"
# lpBuffer : LPSTR optional, out -> "char*"
# nSize : 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)。