📄 filesort.cpp.html

📁 《Big C++ 》Third Edition电子书和代码全集-Part1
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	<title>filesort.cpp</title>
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<pre>  1  #include &lt;algorithm&gt;
  2  #include &lt;fstream&gt;
  3  #include &lt;iostream&gt;
  4  #include &lt;iterator&gt;
  5  #include &lt;queue&gt;
  6  #include &lt;sstream&gt;
  7  #include &lt;vector&gt;
  8  
  9  using namespace std;
 10  
 <font color="#0000cc">11  /**
 12     Create a temporary file name.
 13  */</font>
 14  string temp_name()
 15  {
 16     static int file_count = 0;
 17     ostringstream name;
 18     name &lt;&lt; "temp" &lt;&lt; file_count;
 19     file_count++;
 20     return name.str();
 21  }
 22  
 <font color="#0000cc">23  /**
 24     A generator for strings from standard input
 25  */</font>
 26  class WordGen 
 27  {
 28  public:
 29     string operator()();
 30  };
 31  
 32  string WordGen::operator()()
 33  {
 34     string in;
 35     if (cin &gt;&gt; in)
 36     {
 37        return in;
 38     }
 39     return "";
 40  }
 41  
 42  void phase1(queue&lt;string&gt;&amp; file_names)
 43  {
 44     const int max_words = 10;
 45     WordGen wgen;
 46     while (cin) 
 47     {
 48        <font color="#000099">// Read max_words into vector, sort them, write to temp file </font>
 49        vector&lt;string&gt; a;
 50        generate_n(back_inserter(a), max_words, wgen);
 51        sort(a.begin(), a.end());
 52  
 53        vector&lt;string&gt;::iterator p = unique(a.begin(), a.end());
 54        a.erase(p, a.end());
 55  
 56        string tname = temp_name();
 57        file_names.push(tname);
 58        ofstream out_file(tname.c_str());
 59        copy(a.begin(), a.end(), ostream_iterator&lt;string&gt;(out_file, "\n"));
 60        out_file.close();
 61     }
 62  }
 63  
 64  void phase2(queue&lt;string&gt;&amp; file_names)
 65  {
 66     while (file_names.size() &gt; 1) 
 67     {
 68        <font color="#000099">// Merge two temp files into one</font>
 69        string t1 = file_names.front();
 70        file_names.pop();
 71        string t2 = file_names.front();
 72        file_names.pop();
 73  
 74        ifstream f1(t1.c_str());
 75        ifstream f2(t2.c_str());
 76        string tname = temp_name();
 77        ofstream out_file(tname.c_str());
 78  
 79        merge(istream_iterator&lt;string&gt;(f1), 
 80           istream_iterator&lt;string&gt;(),
 81           istream_iterator&lt;string&gt;(f2), 
 82           istream_iterator&lt;string&gt;(),
 83           ostream_iterator&lt;string&gt;(out_file, "\n"));
 84  
 85        f1.close();
 86        f2.close();
 87        out_file.close();
 88  
 89        <font color="#000099">// Now remove duplicates from resulting file</font>
 90        ifstream in_file(tname.c_str());
 91        string tname2 = temp_name();
 92        ofstream out_file2(tname2.c_str());
 93  
 94        unique_copy(istream_iterator&lt;string&gt;(in_file), 
 95           istream_iterator&lt;string&gt;(),
 96           ostream_iterator&lt;string&gt;(out_file2, "\n"));
 97  
 98        in_file.close();
 99        out_file2.close();
100        file_names.push(tname2);
101     }
102  }
103  
104  int main()
105  {
106     queue&lt;string&gt; file_names;
107  
108     phase1(file_names);
109     phase2(file_names);
110  
111     string tname = file_names.front();
112     ifstream in_file(tname.c_str());
113     copy(istream_iterator&lt;string&gt;(in_file),
114        istream_iterator&lt;string&gt;(),
115        ostream_iterator&lt;string&gt;(cout, "\n"));
116  
117     return 0;
118  }</pre>
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