Re: Questions with Accelerated C++ exercises of chapter 7

On Apr 23, 12:15 pm, Lambda <stephenh...@gmail.com> wrote:


7-4 The output produce by the cross-reference program will be ungainly
if the input file is large. Rewrite the program to break up the output
if the lines get too long.

Original code:

#include <map>
#include <iostream>
#include <string>
#include <vector>

#include "split.h"

using std::cin; using std::cout;
using std::endl; using std::getline;
using std::istream; using std::string;
using std::vector; using std::map;

// find all the lines that refer to each word in the input
map<string, vector<int> >
    xref(istream& in,
         vector<string> find_words(const string&) = split)
{
    string line;
    int line_number = 0;
    map<string, vector<int> > ret;

    // read the next line
    while (getline(in, line)) {
        ++line_number;

        // break the input line into words
        vector<string> words = find_words(line);

        // remember that each word occurs on the current line
        for (vector<string>::const_iterator it = words.begin();
             it != words.end(); ++it)
            ret[*it].push_back(line_number);
    }
    return ret;
}

int main()
{
    // call `xref' using `split' by default
    map<string, vector<int> > ret = xref(cin);

    // write the results
    for (map<string, vector<int> >::const_iterator it = ret.begin();
         it != ret.end(); ++it) {
        // write the word
        cout << it->first << " occurs on line(s): ";

        // followed by one or more line numbers
        vector<int>::const_iterator line_it = it->second.begin();
        cout << *line_it; // write the first line number

        ++line_it;
        // write the rest of the line numbers, if any
        while (line_it != it->second.end()) {
            cout << ", " << *line_it;
            ++line_it;
        }
        // write a new line to separate each word from the next
        cout << endl;
    }

    return 0;
}