Changing size of memory-mapped file on Windows

[nobody]

My email address is barrywhart@yahoo.com.

There is a bug in
mapped_file_source::open_impl(mapped_file_params p)

This function does not correctly check for errors from
SetFilePointer, as documented in the MSDN page below.
(See "Case Two: calling the function with
lpDistanceToMoveHigh != NULL")

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/setfilepointer.asp

Current code:

        ::SetFilePointer(pimpl_->handle_, sizelow,
&sizehigh, FILE_BEGIN);
        if (::GetLastError() != NO_ERROR ||
!::SetEndOfFile(pimpl_->handle_))
            detail::cleanup_and_throw(*pimpl_, "failed
setting file size");

Should be:

        DWORD dwResult =
::SetFilePointer(pimpl_->handle_, sizelow, &sizehigh,
FILE_BEGIN);
        if (dwResult == INVALID_SET_FILE_POINTER
::GetLastError() != NO_ERROR ||
!::SetEndOfFile(pimpl_->handle_))
            detail::cleanup_and_throw(*pimpl_, "failed
setting file size");

--

Even after this fix, the ability to resize an existing
file is not really useful because the file is
apparently recreated rather than resized. I am working
around this by resizing the file using system calls,
but I wonder if this is how the function is supposed to
work?!

[anonymous]

Is this a duplicate of Ticket #856

[Jonathan Turkanis]

this is not a duplicate of #699; #699 deals with file_descriptor, not mapped_file

[Jonathan Turkanis]

Fixed use of SetFilePointer in [42353] in branches/iostreams_dev, to be merged with trunk shortly.

Regarding the ability to resize an existing file, this is anot a supported feature. The new_file_size property of mapped_file_param is just a way to create a new file of a specified size.

I realize that this is an old ticket, so you may not be interested in the issue anymore; however, if you would like to submit a feature request, I will consider it for 1.36. My initial feeling is that it should be a general file-resizing function, not limited to memory-mapped files; in that case, it would probably be best o put it in Boost.Filesystem.