split.h see Note 6 grammar.txt
<noun> cat <noun> dog <noun> table <noun-phrase> <noun> <noun-phrase> <adjective> <noun-phrase> <adjective> large <adjective> brown <adjective> absurd <verb> jumps <verb> sits <location> on the stairs <location> under the sky <location> wherever it wants <sentence> the <noun-phrase> <verb> <location>main.cpp
#include <iostream> #include <map> #include <string> #include <vector> #include <stdlib.h> #include <stdexcept> #include <fstream> #include "split.h" using std::cout; using std::endl; using std::domain_error; using std::string; using std::vector; using std::istream; using std::map; using std::ifstream; using std::logic_error; using std::cerr; typedef vector<string> Rule; typedef vector<Rule> Rule_collection; typedef map<string, Rule_collection> Grammar; Grammar read_grammar(ifstream& infile) { Grammar ret; string line; while(getline(infile, line)) { vector<string> entry = split(line); if(!entry.empty()) { Rule rules(entry.begin() + 1, entry.end()); ret[entry[0]].push_back(rules); } } return ret; } int nrand(int n) { if (n < 0 || n > RAND_MAX) throw domain_error("Argument to nrand is out of range"); const int bucket_size = RAND_MAX / n; int r; do r = rand() / bucket_size; while (r > n); return r; } bool bracketed(const string& s) { return s[0] == '<' && s[s.size() - 1] == '>'; } void gen_aux(const Grammar& g, const string& s, vector<string>& v) { if (bracketed(s)){ Grammar::const_iterator it = g.find(s); if (it == g.end()) throw logic_error("empty error"); const Rule_collection& rc = it->second; const Rule r = rc[nrand(rc.size())]; for (Rule::size_type i = 0; i != r.size(); ++i) gen_aux(g, r[i], v); } else v.push_back(s); } vector<string> gen_sentence(const Grammar& g) { vector<string> ret; gen_aux(g, "<sentence>", ret); return ret; } int main() { string ifile = "grammar.txt"; ifstream infile(ifile.c_str()); // check that the open succeede if (!infile) { cerr << "error: unable to open input file: " << ifile << endl; return -1; } // generate the sentence Grammar g = read_grammar(infile); vector<string> sentence = gen_sentence(g); // write the first word, if any vector<string>::const_iterator it = sentence.begin(); if(!sentence.empty()) { cout << *it; ++it; } // write the rest of the word, each preceded by a space while (it != sentence.end()) { cout << " " << *it; ++it; } cout << endl; return 0; }