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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. using namespace std;
  5.  
  6. class BufferedStreamBuf : public streambuf
  7. {
  8.   streambuf *buf;
  9.   vector<int_type> buffer;
  10.   streampos pos;
  11. public:
  12.   BufferedStreamBuf(streambuf* buf):  buf(buf), pos(0) { }
  13.   BufferedStreamBuf(const BufferedStreamBuf&) = delete;
  14.   BufferedStreamBuf& operator=(const BufferedStreamBuf&) = delete;
  15. protected:
  16.   virtual int_type underflow() 
  17.   {
  18.     if (pos == buffer.size())
  19.       {
  20.         int_type c = buf->sbumpc();
  21.         buffer.push_back(c);
  22.         return c;  
  23.       }
  24.     else if (pos < buffer.size())
  25.       {
  26.         return buffer[pos];
  27.       }
  28.     else
  29.       {
  30.         return EOF;
  31.       }
  32.   }
  33.   virtual int_type uflow() 
  34.   {
  35.       if (pos >= buffer.size())
  36.       {
  37.         int_type c = buf->sbumpc();
  38.         buffer.push_back(c);
  39.         pos += 1;
  40.         return c;  
  41.       }
  42.     else
  43.       {
  44.         return buffer[pos+=1];
  45.       }
  46.   }  
  47.   virtual streampos seekoff(streamoff off, ios_base::seekdir way, ios_base::openmode which)
  48.   {
  49.     if (which == ios_base::in)
  50.       {
  51.         if (way == ios_base::beg and off >= 0)
  52.           {
  53.             while (off >= buffer.size())
  54.               uflow();
  55.             pos = off;             
  56.           }
  57.         if (way == ios_base::cur)
  58.           {
  59.             streampos new_pos = off + pos;
  60.             while (new_pos >= buffer.size())
  61.               uflow();
  62.             pos = new_pos;
  63.           }
  64.        if (way == ios_base::end)
  65.           {
  66.             // Kann man später noch richtig machen. Erst einmal Fehler
  67.             return pos_type(off_type(-1));
  68.           }        
  69.       }
  70.     return 0;
  71.   }
  72.  virtual streampos seekpos(streampos newp, ios_base::openmode which)
  73.   {
  74.     cerr << "Seekpos called.\n";
  75.     if (which == ios_base::in)
  76.       {
  77.         while (newp >= buffer.size())
  78.           uflow();
  79.         pos = newp;             
  80.       }
  81.     return 0;
  82.   }
  83.  };
  84.  
  85.  
  86. int main()
  87. {
  88.   BufferedStreamBuf buffered_cin_streambuf(cin.rdbuf());
  89.   istream buffered_cin(&buffered_cin_streambuf);
  90.   int i;
  91.   buffered_cin >> i;
  92.   cout << i << '\n';
  93.   int j;
  94.   buffered_cin.seekg(1, ios::beg);
  95.   buffered_cin >> j;
  96.   cout << j << '\n';
  97. }
  98.  
Success #stdin #stdout 0s 2992KB
comments (?)
stdin 
123
stdout 
123
23
https://ideone.com/p4wpZu
language:
C++14 (gcc 8.3)
created:
13 years ago
visibility:
public

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