[Boost-bugs] [Boost C++ Libraries] #3323: file_descriptor_sink sink("abc", BOOST_IOS::trunc) not trunc

Subject: [Boost-bugs] [Boost C++ Libraries] #3323: file_descriptor_sink sink("abc", BOOST_IOS::trunc) not trunc
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-08-07 02:11:59

#3323: file_descriptor_sink sink("abc", BOOST_IOS::trunc) not trunc
--------------------------------------------+-------------------------------
 Reporter:  qiaozhiqiang@…                  |       Owner:  turkanis 
     Type:  Bugs                            |      Status:  new      
Milestone:  Boost 1.40.0                    |   Component:  iostreams
  Version:  Boost 1.39.0                    |    Severity:  Problem  
 Keywords:  file_descriptor_sink not trunc  |  
--------------------------------------------+-------------------------------
 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;

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

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3323>
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