PathAddExtensionA

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

BOOL PathAddExtensionA(
    LPSTR pszPath,
    LPCSTR pszExt   // optional
);

<DllImport("SHLWAPI.dll", CharSet:=CharSet.Ansi, ExactSpelling:=True)>
Public Shared Function PathAddExtensionA(
    <MarshalAs(UnmanagedType.LPStr)> pszPath As System.Text.StringBuilder,   ' LPSTR in/out
    <MarshalAs(UnmanagedType.LPStr)> pszExt As String   ' LPCSTR optional
) As Boolean
End Function

' pszPath : LPSTR in/out
' pszExt : LPCSTR optional
Declare PtrSafe Function PathAddExtensionA Lib "shlwapi" ( _
    ByVal pszPath As String, _
    ByVal pszExt As String) As Long
' VBA7前提(PtrSafe)。32bit Office では LongPtr→Long。Integer=16bit / Long=32bit / LongLong=64bit。

import ctypes
from ctypes import wintypes

PathAddExtensionA = ctypes.windll.shlwapi.PathAddExtensionA
PathAddExtensionA.restype = wintypes.BOOL
PathAddExtensionA.argtypes = [
    wintypes.LPSTR,  # pszPath : LPSTR in/out
    wintypes.LPCSTR,  # pszExt : LPCSTR optional
]

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('SHLWAPI.dll')
PathAddExtensionA = Fiddle::Function.new(
  lib['PathAddExtensionA'],
  [
    Fiddle::TYPE_VOIDP,  # pszPath : LPSTR in/out
    Fiddle::TYPE_VOIDP,  # pszExt : LPCSTR optional
  ],
  Fiddle::TYPE_INT)

#[link(name = "shlwapi")]
extern "system" {
    fn PathAddExtensionA(
        pszPath: *mut u8,  // LPSTR in/out
        pszExt: *const u8  // LPCSTR optional
    ) -> i32;
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[return: MarshalAs(UnmanagedType.Bool)]
[DllImport("SHLWAPI.dll", CharSet = CharSet.Ansi)]
public static extern bool PathAddExtensionA([MarshalAs(UnmanagedType.LPStr)] System.Text.StringBuilder pszPath, [MarshalAs(UnmanagedType.LPStr)] string pszExt);
"@
$api = Add-Type -MemberDefinition $sig -Name 'SHLWAPI_PathAddExtensionA' -Namespace Win32 -PassThru
# $api::PathAddExtensionA(pszPath, pszExt)

#uselib "SHLWAPI.dll"
#func global PathAddExtensionA "PathAddExtensionA" sptr, sptr
; PathAddExtensionA varptr(pszPath), pszExt   ; 戻り値は stat
; pszPath : LPSTR in/out -> "sptr"
; pszExt : LPCSTR optional -> "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 "SHLWAPI.dll"
#cfunc global PathAddExtensionA "PathAddExtensionA" var, str
; res = PathAddExtensionA(pszPath, pszExt)
; pszPath : LPSTR in/out -> "var"
; pszExt : LPCSTR optional -> "str"
; ※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。

; BOOL PathAddExtensionA(LPSTR pszPath, LPCSTR pszExt)
#uselib "SHLWAPI.dll"
#cfunc global PathAddExtensionA "PathAddExtensionA" var, str
; res = PathAddExtensionA(pszPath, pszExt)
; pszPath : LPSTR in/out -> "var"
; pszExt : LPCSTR optional -> "str"
; ※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 (
	shlwapi = windows.NewLazySystemDLL("SHLWAPI.dll")
	procPathAddExtensionA = shlwapi.NewProc("PathAddExtensionA")
)

// pszPath (LPSTR in/out), pszExt (LPCSTR optional)
r1, _, err := procPathAddExtensionA.Call(
	uintptr(pszPath),
	uintptr(unsafe.Pointer(windows.BytePtrFromString(pszExt))),
)
_ = err  // syscall.Errno (valid when the call sets last-error)
_ = r1   // BOOL

function PathAddExtensionA(
  pszPath: PAnsiChar;   // LPSTR in/out
  pszExt: PAnsiChar   // LPCSTR optional
): BOOL; stdcall;
  external 'SHLWAPI.dll' name 'PathAddExtensionA';

result := DllCall("SHLWAPI\PathAddExtensionA"
    , "Ptr", pszPath   ; LPSTR in/out
    , "AStr", pszExt   ; LPCSTR optional
    , "Int")   ; return: BOOL

●PathAddExtensionA(pszPath, pszExt) = DLL("SHLWAPI.dll", "bool PathAddExtensionA(char*, char*)")
# 呼び出し: PathAddExtensionA(pszPath, pszExt)
# pszPath : LPSTR in/out -> "char*"
# pszExt : LPCSTR optional -> "char*"
# 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)。