Get modification time of locked folder with boost::filesystem::last_write_time

Question

When I'm using

time_t t = last_write_time("C:\\System Volume Information");

I get the following exception:

boost::filesystem::last_write_time: Access denied: "C:\System Volume Information"

Nevertheless, Windows Explorer is able to get access to that information. It looks like Boost requires extra access to the folder, and that's the reason the code doesn't work.

Is it possible to make a workaround somehow?

Edit. Here's a citation from libs\filesystem\src\operations.cpp:1312:

handle_wrapper hw(
  create_file_handle(p.c_str(), 0,
    FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE, 0,
    OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0));

I don't see what's wrong with it yet.

Answer 1

That folder is off limits even to users with an Admin account, it contains restore points. Not that you couldn't change the ACL with such an account but that is of course not the correct solution. Trying to open a handle on the directory is too heavy-handed, use FindFirstFile() instead. Like this:

WIN32_FIND_DATA info;
auto hdl = FindFirstFile(L"C:\\System Volume Information", &info);
if (hdl == INVALID_HANDLE_VALUE) throw win32_error(GetLastError());
SYSTEMTIME time;
FileTimeToSystemTime(&info.ftLastWriteTime, &time);
// etc..
//...
FindClose(hdl);