11.6 Patterns for Extractors and Inserters of User-Defined Types

Here is the pattern for an extractor:

template<class charT, class Traits>
basic_istream<charT, Traits>& operator >> 
  (basic_istream<charT, Traits >& is, UserDefinedType& x)
{
 ios_base::iostate err = 0;
 
 try {
 
  typename basic_istream<charT, Traits>::sentry ipfx(is);
 
  if(ipfx)
  {
   // Do whatever has to be done!
   // Typically you will access the stream's locale or buffer.
   // Don't call stream member functions here in MT environments!

   // Add state bits to the err variable if necessary, e.g.
   // if () err |= ios_base::failbit;
  }
 } // try
 catch(...)                                                   //1
 {
    bool flag = FALSE;
    try { is.setstate(ios_base::failbit); }                   //2
    catch( ios_base::failure ) { flag= TRUE; }                //3
    if ( flag ) throw;                                        //4
 }
 
 if ( err ) is.setstate(err);                                 //5
 
 return is;
}

Similarly, the pattern for the inserter looks like this:

template<class charT, class Traits>
basic_ostream<charT, Traits>& operator << 
 (basic_ostream<charT, Traits >& os, const UserDefinedType& x)
{
 ios_base::iostate err = 0;
 
 try {
  typename basic_ostream<charT, Traits>::sentry opfx(os);
 
  if(opfx)
  {
   // Do whatever has to be done!
   // Typically you will access the stream's locale or buffer.
   // Don't call stream member functions here in MT environments!

   // Add state bits to the err variable if necessary, e.g.
   // if () err |= ios_base::failbit;

   // Reset the field width after usage, i.e.
   // os.width(0);
  }
 } //try
 catch(...)
 {
    bool flag = FALSE;
    try { os.setstate(ios_base::failbit); }
    catch( ios_base::failure ) { flag= TRUE; }
    if ( flag ) throw;
 }
 
 if ( err ) os.setstate(err);
 
 return os;
}

©Copyright 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.