// Purpose: Read words and write in reverse order. A word contains only alphabetic characters.
//
// Command syntax:
//    $ ./a.out [ input-file [ output-file ] ]
// all parameters are optional. Defaults: input-file => cin, output-file => cout
//
// Examples:
//    $ ./a.out
//    $ ./a.out inputfile
//    $ ./a.out inputfile outputfile

#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <string>
#include <list>
#include <cstdlib>					// exit
using namespace std;					// direct access to std

bool convert( int &val, char *buffer ) {		// convert C string to integer
    std::stringstream ss( buffer );			// connect stream and buffer
    string temp;
    ss >> dec >> val;					// convert integer from buffer
    return ! ss.fail() &&				// conversion successful ?
	! ( ss >> temp );				// characters after conversion all blank ?
} // convert

int main( int argc, char *argv[] ) {
    istream *infile = &cin;				// default value
    ostream *outfile = &cout;				// default value

    infile->exceptions( ios_base::failbit );		// set cin/cout to use exceptions
    outfile->exceptions( ios_base::failbit );
    try {
	switch ( argc ) {
	  case 3:
	    try {
		outfile = new ofstream( argv[2] );	// open output file
		outfile->exceptions( ios_base::failbit ); // set exceptions
	    } catch( ios_base::failure ) {
		throw ios_base::failure( "could not open output file" );
	    } // try
	    // FALL THROUGH
	  case 2:
	    try {
		infile = new ifstream( argv[1] );	// open input file
		infile->exceptions( ios_base::failbit ); // set exceptions
	    } catch( ios_base::failure ) {
		throw ios_base::failure( "could not open input file" );
	    } // try
	    // FALL THROUGH
	  case 1:					// all defaults
	    break;
	  default:					// wrong number of options
	    throw ios_base::failure( "wrong number of arguments" );
	} // switch
    } catch( ios_base::failure err ) {
	cerr << err.what() << endl;
	cerr << "Usage: " << argv[0] << " [ input-file [ output-file ] ]" << endl;
	exit( EXIT_FAILURE );				// TERMINATE
    } // try

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

    *infile >> noskipws;				// turn off white space skipping during input

    try {
	for ( ;; ) {					// process lines from input
	    getline( *infile, line );			// read entire line, but not newline
	    line += "\n";				// add newline as sentinel
	    for ( ;; ) {				// scan words in line
		string::size_type posn = line.find_first_of(alpha); // find position of 1st alphabetic character
	      if ( posn == string::npos ) 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
    } catch( ios_base::failure ) {}			// end of file

    *outfile << "Words in reverse order:" << endl;

    // traverse list in reverse
    for ( list<string>::reverse_iterator iter = words.rbegin(); iter != words.rend(); iter++ ) {
        cout << *iter << endl;				// print word
    } // for

    if ( infile != &cin ) delete infile;		// close file, do not delete cin!
    if ( outfile != &cout ) delete outfile;		// close file, do not delete cout!
} // main