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copied!<p><code>std::string</code> already includes a working overload of <code>operator<</code>, so you can just compare strings directly. Java uses <code>compareTo</code> primarily because the built-in comparison operator produces results that aren't generally useful for strings. Being a lower-level language, Java doesn't support user-defined operator overloads, so it uses <code>compareTo</code> as a band-aid to cover for the inadequacy of the language.</p> <p>From your description, however, you don't need to deal with <em>any</em> of that directly at all. At least as you've described the problem, you really want is something like:</p> <pre><code>std::map<std::string, std::vector<int> > page_map; </code></pre> <p>You'll then read words in from your text file, and insert the page number where each occurs into the page map:</p> <pre><code>page_map[current_word].push_back(current_page); </code></pre> <p>Note that I've used <code>std::map</code> above, on the expectation that you may want ordered results (e.g., be able to quickly find all words from <code>age</code> to <code>ale</code> in alphabetical order). If you don't care about ordering, you may want to use <code>std::unordered_map</code> instead.</p> <p>Edit: here's a simple text cross-reference program that reads a text file (from standard input) and writes out a cross-reference by line number (i.e., each "word", and the numbers of the lines on which that word appeared).</p> <pre><code>#include <map> #include <unordered_map> #include <iostream> #include <string> #include <vector> #include <sstream> #include <iterator> #include "infix_iterator.h" typedef std::map<std::string, std::vector<unsigned> > index; namespace std { ostream &operator<<(ostream &os, index::value_type const &i) { os << i.first << ":\t"; std::copy(i.second.begin(), i.second.end(), infix_ostream_iterator<unsigned>(os, ", ")); return os; } } void add_words(std::string const &line, size_t num, index &i) { std::istringstream is(line); std::string temp; while (is >> temp) i[temp].push_back(num); } int main() { index i; std::string line; size_t line_number = 0; while (std::getline(std::cin, line)) add_words(line, ++line_number, i); std::copy(i.begin(), i.end(), std::ostream_iterator<index::value_type>(std::cout, "\n")); return 0; } </code></pre> <p>If you look at the first <code>typedef</code> (of <code>index</code>), you can change it from <code>map</code> to <code>unordered_map</code> if you want to test a hash table vs. a red-black tree. Note that this interprets "word" pretty loosely -- basically any sequence of non-whitespace characters, so for example, it'll treat <code>example,</code> as a "word" (and it'll be separate from <code>example</code>).</p> <p>Note that this uses the <code>infix_iterator</code> I've posted <a href="https://codereview.stackexchange.com/q/13176/489">elsewhere</a>.</p>

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