id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
3323	"file_descriptor_sink sink(""abc"", BOOST_IOS::trunc) not trunc"	qiaozhiqiang@…	Jonathan Turkanis	"boost 1.39.0 iostreams, on Windows Vista sp2:
file_descriptor_sink sink(""abc"", BOOST_IOS::trunc) not trunc,

and file_descriptor_sink sink(""abc"", BOOST_IOS::app) only need call SetFilePointer(pimpl_->handle_, 0, NULL, FILE_END) once, but now every write() call it once, why? 
if write only, can we call SetFilePointer() in open() only once, and not set the flag impl::append?


void file_descriptor::open
    ( const std::string& path, BOOST_IOS::openmode m,
      BOOST_IOS::openmode base )
{
    using namespace std;
    m |= base;
#ifdef BOOST_IOSTREAMS_WINDOWS //---------------------------------------------//
    DWORD dwDesiredAccess;
    DWORD dwCreationDisposition;
    if ( (m & (BOOST_IOS::in | BOOST_IOS::out))
             ==
         (BOOST_IOS::in | BOOST_IOS::out) )
    {
        if (m & BOOST_IOS::app)
            throw BOOST_IOSTREAMS_FAILURE(""bad open mode"");
        dwDesiredAccess = GENERIC_READ | GENERIC_WRITE;
        dwCreationDisposition =
            (m & BOOST_IOS::trunc) ?
                OPEN_ALWAYS :
                OPEN_EXISTING;
    } else if (m & BOOST_IOS::in) {
        if (m & (BOOST_IOS::app |BOOST_IOS::trunc))
            throw BOOST_IOSTREAMS_FAILURE(""bad open mode"");
        dwDesiredAccess = GENERIC_READ;
        dwCreationDisposition = OPEN_EXISTING;
    } else if (m & BOOST_IOS::out) {
        dwDesiredAccess = GENERIC_WRITE;
        dwCreationDisposition = OPEN_ALWAYS;
        if (m & BOOST_IOS::app)
            pimpl_->flags_ |= impl::append;
    } else {
        throw BOOST_IOSTREAMS_FAILURE(""bad open mode"");
    }

    HANDLE handle =
        ::CreateFileA( path.c_str(),
                       dwDesiredAccess,
                       FILE_SHARE_READ | FILE_SHARE_WRITE,
                       NULL,                   // lpSecurityAttributes
                       dwCreationDisposition,
                       FILE_ATTRIBUTE_NORMAL,
                       NULL );                 // hTemplateFile
    if (handle != INVALID_HANDLE_VALUE) {
        pimpl_->handle_ = handle;
        pimpl_->flags_ |= impl::close_on_exit;
    } else {
        pimpl_->flags_ = 0;
        throw BOOST_IOSTREAMS_FAILURE(""bad open"");
    }

..................

std::streamsize file_descriptor::write(const char_type* s, std::streamsize n)
{
#ifdef BOOST_IOSTREAMS_WINDOWS
    if (pimpl_->flags_ & impl::append) {
        DWORD const dwResult =
            ::SetFilePointer(pimpl_->handle_, 0, NULL, FILE_END);
        if ( dwResult == INVALID_SET_FILE_POINTER &&
             ::GetLastError() != NO_ERROR )
        {
            throw detail::bad_seek();
        }
    }
    DWORD ignore;
    if (!::WriteFile(pimpl_->handle_, s, n, &ignore, NULL))
        throw detail::bad_write();
    return n;

..............."	Bugs	closed	Boost 1.40.0	iostreams	Boost 1.39.0	Problem	fixed	file_descriptor_sink not trunc