[boost] [iostreams] mapped_file_source fails for zero sized file

Subject: [boost] [iostreams] mapped_file_source fails for zero sized file
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2013-02-11 04:00:58

While testing out iostreams memory mapped file source I ran into an 
issue where it throws when opening a zero sized file (testing on windows 
7 vc11 x64).

for example something like:

namespace io = boost::iostreams;
namespace fs = boost::filesystem;
fs::path path("C:\\boost\\boost_1_53_0\\libs\\context\\src\\dummy.cpp");
io::stream<io::mapped_file_source> file( path );

Will throw:

failed create mapping: The volume for a file has been externally altered 
so that the opened file is no longer valid.

From:

http://tinyurl.com/cx2b9ru

"When you do not want the size of the file to change (for example, when 
mapping read-only files), call CreateFileMapping and specify zero for 
both dwMaximumSizeHigh and dwMaximumSizeLow. Doing this creates a file 
mapping object that is exactly the same size as the file. Otherwise, you 
must calculate or estimate the size of the finished file because file 
mapping objects are static in size; once created, their size cannot be 
increased or decreased. An attempt to map a file with a length of zero 
in this manner fails with an error code of ERROR_FILE_INVALID. Programs 
should test for files with a length of zero and reject such files."

I don't see anything in the docs that would lead me to believe this 
should throw. Rather I would expect:

std::istream_iterator<char>(file) == std::istream_iterator<char>()