cppreference.com > C++ I/O > clear clear Syntax:
      #include <fstream>
      void clear( iostate flags = ios::goodbit );
The function clear() does two things: it clears all io stream state flags associated with the current stream, and sets the flags denoted by flags The flags argument defaults to ios::goodbit, which means that by default, all flags will be cleared and ios::goodbit will be set. Example code: For example, the following code uses the clear() function to reset the flags of an output file stream, after an attempt is made to read from that output stream:
     fstream outputFile( "output.txt", fstream::out );

     // try to read from the output stream; this shouldn't work
     int val;
     outputFile >> val;
     if( outputFile.fail() ) {
       cout << "Error reading from the output stream" << endl;
       // reset the flags associated with the stream
       outputFile.clear();
     }

     for( int i = 0; i < 10; i++ ) {
       outputFile << i << " ";
     }
     outputFile << endl;
Related topics: eof fail good rdstate