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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. // Identify the type of element in given range type.
  5. template<typename Range> struct range_elem {
  6.     typedef typename std::decay<decltype(*std::begin(std::declval<Range &>()))>::type type;
  7. };
  8.  
  9. // Count the number of elements in range matching value.
  10. template<typename Range>
  11. int count(const Range& range, typename range_elem<Range>::type value) {
  12.     int n = 0;
  13.     for (const auto& e : range) { if (e==value) n++; }
  14.     return n;
  15. }
  16.  
  17. int main() {
  18.     // This compiles OK.
  19.     std::vector<int> vec; vec.push_back(1); vec.push_back(2); vec.push_back(3);
  20.     std::cerr << count(vec, 2) << "\n";
  21.     //
  22.     int ar[3] = {1,2,3};
  23.     // This compiles OK.
  24.     {
  25.         int n = 0;
  26.         for (const auto& e : ar) { if (e==2) n++; }
  27.         std::cerr << n << "\n";
  28.     }
  29.     // This fails to compile on gcc 4.8.1;
  30.     //  error: no matching function for call to 'begin(int [3])'
  31.     std::cerr << count(ar, 2) << "\n";
  32.     return 0;
  33. }
Success #stdin #stdout #stderr 0s 3468KB
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https://ideone.com/RoNFZz
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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