WinAPI: GetSystemDirectory - 返回 System 文件夹路径

//声明:
GetSystemDirectory(
  lpBuffer: PChar; {缓冲区}
  uSize: UINT      {缓冲区大小}
): UINT;           {返回实际长度}


//举例:
var
  arr: array[0..MAX_PATH] of Char;
  num: UINT;
begin
  num := GetSystemDirectory(arr, MAX_PATH);
  ShowMessage(arr);           {C:\WINDOWS\system32}
  ShowMessage(IntToStr(num)); {19}
end;