/*******************
  Words are read in and written out in reverse order. A word contains only alphabetic characters.
  Command line syntax is:

  ./a.out [input-file [output-file]]

  input-file is the optional name of the input file (defaults to cin).  If output-file is specified,
  the input file must also be specified. The output file defaults to cout if not specified.

  Examples:
	./a.out
	./a.out inputfile
	./a.out inputfile outputfile
*******************/

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <list>
using namespace std;

int main( int argc, char *argv[] ) {
	istream	*infile = &cin;								// pointer to input stream; default to cin
	ostream	*outfile = &cout;							// pointer to output stream; default to cout

	switch ( argc ) {
	  case 3:
		outfile = new ofstream( argv[2] );				// open the outfile file
		if ( outfile->bad() ) {
			cerr << "Error! Could not open output file \"" << argv[2] << "\"" << endl;
			exit( -1 );									// TERMINATE!
		} // if
		// fall through to handle input file
	  case 2:
		infile = new ifstream( argv[1] );				// open the first input file
		if ( infile->bad() ) {
			cerr << "Error! Could not open input file \"" << argv[1] << "\"" << endl;
			exit( -1 );									// TERMINATE!
		} // if
		break;
	  case 1:
		// use cin and cout
		break;
	  default:											// too many arguments
		cerr << "Usage: " << argv[0] << " [input-file [output-file]]" << endl;
		exit( -1 );										// TERMINATE!
	}

	string line, alpha = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
	list<string> words;									// list of words in document

	for ( ;; ) {										// scan lines from a file
		getline( *infile, line );						// read entire line, but not newline
	  if ( infile->eof() ) break;						// end-of-file ?
		line += "\n";									// add newline character as sentinel character
		for ( ;; ) {									// scan words off line
			int posn = line.find_first_of(alpha);		// find position of 1st alphabetic character
		  if ( posn == -1 ) break;						// any characters left ?
			line = line.substr( posn );					// remove leading whitespace
			posn = line.find_first_not_of(alpha);		// find position of 1st non-alphabetic character
			string word = line.substr( 0, posn );		// extract word from start of line
			words.push_back( word );					// add word to end of list
			line = line.substr( posn );					// delete word from line
		} // for
	} // for

	*outfile << "The words in reverse order:" << endl;

	while ( 0 < words.size() ) {						// traverse list in reverse order
		*outfile << *(--words.end()) << endl;			// print last node
		words.erase( --words.end() );					// remove last node
	} // whille
	
	if ( infile != &cin ) delete infile;				// do not delete cin
	if ( outfile != &cout ) delete outfile;				// do not delete cout
} // main

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