JD wrote:

I tried without the new_file_size, I tried with a mapped_file... Is there something I don't get? Why are we not able to open a file that already exist?

I assume you have mapped_file.cpp in your project already (otherwise I don't think you could link). Upon quick inspection, your example seems to mimic some of the test code almost identically (i.e. in mapped_file_test.cpp), so I think it should work... What happens when you try to run the unit tests in the boost_1_34_1\libs\iostreams\test subdirectory of the source tarball? Do they pass?