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  1. #include <iostream>
  2. #include <tuple>
  3. #include <functional>
  4. #include <type_traits>
  5. #include <stdexcept>
  6.  
  7. template<bool B>
  8. using Bool = std::integral_constant<bool, B>;
  9.  
  10. template<typename T>
  11. using EnableIf = typename std::enable_if<T::value>::type;
  12.  
  13. template<size_t N = 0, class Elem, class Traits, typename... Args, EnableIf<Bool<(N >= sizeof...(Args))>>...>
  14. inline void index_input(std::basic_istream<Elem,Traits>&, const size_t, const std::tuple<Args...>&) {
  15.     throw std::out_of_range("Index exceeds number of arguments provided");
  16. }
  17.  
  18. template<size_t N = 0, class Elem, class Traits, typename... Args, EnableIf<Bool<(N < sizeof...(Args))>>...>
  19. inline void index_input(std::basic_istream<Elem,Traits>& in, const size_t i, const std::tuple<Args...>& tup) {
  20.     if(i != N) {
  21.         index_input<N + 1>(in, i, tup);
  22.         return;
  23.     }
  24.     using std::get;
  25.     in >> get<N>(tup);
  26. }
  27.  
  28. template<typename CharT, typename Elem, /*size_t N,*/ typename... Args>
  29. void fscan(std::basic_istream<CharT, Elem>& in, const std::basic_string<CharT, Elem>& format, Args&&... args) {
  30.     // make a tuple of references
  31.     auto tup = std::make_tuple(std::ref(std::forward<Args>(args))...);
  32.     auto first = format.cbegin();
  33.     auto last = format.cend();
  34.     unsigned index = 0;
  35.  
  36.     for(; first != last; ++first) {
  37.         if(*first == '%' && ((first + 1) != last || *(first + 1) != '%')) {
  38.             // format specifier
  39.             index_input(in, index++, tup);
  40.             continue;
  41.         }
  42.  
  43.         // non-format specifier or parsing error
  44.         auto c = in.get();
  45.         if(!in || c != *first) {
  46.             throw std::runtime_error("error parsing");
  47.             break;
  48.         }
  49.     }
  50. }
  51.  
  52. int main() {
  53.     int x, y;
  54.     fscan(std::cin, std::string("% = %"), x, y);
  55.     std::cout << x << " = " << y;
  56. }
Success #stdin #stdout 0s 3436KB
comments (?)
stdin 
10 = 11
stdout 
10 = 11
https://ideone.com/OCbu3A
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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