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  1. #include <fstream>
  2. #include <iostream>
  3. #include <sstream>
  4. #include <limits>
  5.  
  6. struct double_istream 
  7. {
  8.   std::istream &in;
  9.  
  10.   double_istream (std::istream &i) : in(i) {}
  11.  
  12.   double_istream & parse_on_fail (double &x, bool neg)
  13.   {
  14.     const char *exp[] = {"", "inf", "Inf", "NaN", "nan"};
  15.     const char *e = exp[0];
  16.     int l = 0;
  17.     char parsed[4];
  18.     char *c = parsed;
  19.     if (neg) *c++ = '-';
  20.     in.clear();
  21.     if (!(in >> *c).good()) return *this; //If the stream is broken even before trying to read from it, it's pointless to try.
  22.  
  23.     switch (*c) //Switch on the first character to parse, if 'i' or 'I', set up for Infinity, else if 'n' or 'N', set up for NaN
  24.     {
  25.       case 'i': e = exp[l=1]; break;
  26.       case 'I': e = exp[l=2]; break;
  27.       case 'N': e = exp[l=3]; break;
  28.       case 'n': e = exp[l=4]; break;
  29.     }
  30.  
  31.     while (*c == *e) 
  32.     {
  33.       if ((e-exp[l]) == 2) break;
  34.       ++e; 
  35.       if (!(in >> *++c).good()) break;
  36.     }
  37.  
  38.     if (in.good() && *c == *e) 
  39.     {
  40.       switch (l) 
  41.       {
  42.         case 1: case 2: x = std::numeric_limits<double>::infinity(); break;
  43.         case 3: case 4: x = std::numeric_limits<double>::quiet_NaN(); break;
  44.       }
  45.       if (neg) x = -x;
  46.       return *this;
  47.     } 
  48.     else if (!in.good()) 
  49.     {
  50.       if (!in.fail()) return *this;
  51.       in.clear(); --c;
  52.     }
  53.  
  54.     do { in.putback(*c); } while (c-- != parsed);
  55.     in.setstate(std::ios_base::failbit);
  56.     return *this;
  57.   }
  58.  
  59.   double_istream & operator >> (double &x) {
  60.     bool neg = false;
  61.     char c;
  62.     if (!in.good()) return *this;
  63.     while (isspace(c = in.peek())) in.get();
  64.     if (c == '-') { neg = true; }
  65.     in >> x;
  66.     if (! in.fail()) return *this;
  67.     return parse_on_fail(x, neg);
  68.   }
  69. };
  70.  
  71. struct double_imanip 
  72. {
  73.   mutable std::istream *in;
  74.  
  75.   const double_imanip & operator >> (double &x) const 
  76.   {
  77.     double_istream(*in) >> x;
  78.     return *this;
  79.   }
  80.  
  81.   std::istream & operator >> (const double_imanip &) const 
  82.   {
  83.     return *in;
  84.   }
  85. };
  86.  
  87. const double_imanip & operator >> (std::istream &in, const double_imanip &dm) 
  88. {
  89.   dm.in = &in;
  90.   return dm;
  91. }
  92.  
  93. int main()
  94. {
  95. std::stringstream iss("1.0 -NaN inf Inf nan -inf NaN 1.2 inf");
  96. double u, v, w, x, y, z, a, b, fail_double;
  97. std::string fail_string;
  98. iss >> double_imanip()
  99.     >> u >> v >> w >> x >> y >> z >> a >> b
  100.     >> double_imanip()
  101.     >> fail_double;
  102. std::cout << u << " " << v << " " << w << " "
  103.           << x << " " << y << " " << z << " " << a << " " << b << std::endl;
  104. if (iss.fail()) {
  105.     iss.clear();
  106.     iss >> fail_string;
  107.     std::cout << fail_string << std::endl;
  108. } else {
  109.     std::cout << "TEST FAILED" << std::endl;
  110. }
  111. }
Success #stdin #stdout 0.01s 2864KB
comments (?)
stdin
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Standard input is empty
stdout
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1 nan inf inf nan -inf nan 1.2
inf
https://ideone.com/qIFVo
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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