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  1. #include<iostream>
  2. #include<type_traits>
  3.  
  4. // Think that another thread reads this array
  5. template<typename T, size_t M>
  6. inline void zero_func(volatile T (&arr)[M]) {
  7.     for(auto &i : arr) i = 0;
  8. }
  9.  
  10. template<typename T, size_t M>
  11. inline void zero_func(volatile T *ptr) {
  12.     zero_func(reinterpret_cast<volatile T (&)[M]>(*ptr));
  13. }
  14.  
  15. template<typename T, size_t M>
  16. inline void compare_types(volatile T (&arr)[M]) {
  17.     volatile char a[M] = {0};
  18.     volatile char *b = a;
  19.     volatile char * volatile c = a;
  20.     decltype(a) d;
  21.     std::cout << std::boolalpha;
  22.     std::cout << "Which type is equivalent to: volatile char a[M]?" << std::endl;
  23.     std::cout << "volatile char *b: \t\t" << std::is_same<decltype(a), decltype(b)>::value << std::endl;    
  24.     std::cout << "volatile char * volatile c: \t" << std::is_same<decltype(a), decltype(c)>::value << std::endl;    
  25.     std::cout << "decltype(a): \t\t\t" << std::is_same<decltype(a), decltype(d)>::value << std::endl;   
  26.  
  27.     // volatile char a[100] and volatile T (&arr)[M] are same types, excluding reference
  28.     typedef decltype(arr) T_vol_ref;
  29.     typedef typename std::remove_reference<T_vol_ref>::type T_vol;
  30.     std::cout << "volatile T (&arr)[M]: \t\t" << std::is_same<decltype(a), T_vol>::value << std::endl;  
  31. }
  32.  
  33. int main() {
  34.     char for_zero[100] = {1};
  35.  
  36.     // secure zero
  37.     zero_func<char, 100>(for_zero);
  38.     std::cout << (unsigned)for_zero[0] << std::endl;
  39.  
  40.     char *for_zero2 = new char[100];
  41.     for_zero2[0] = 1;
  42.     zero_func<char, 100>(for_zero2);
  43.     std::cout << (unsigned)for_zero2[0] << std::endl;
  44.     delete for_zero2;
  45.  
  46.     compare_types(for_zero);
  47.  
  48.     return 0;
  49. }
Success #stdin #stdout 0s 3028KB
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Which type is equivalent to: volatile char a[M]?
volatile char *b: 		false
volatile char * volatile c: 	false
decltype(a): 			true
volatile T (&arr)[M]: 		true
https://ideone.com/V12vIX
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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