60 lines
2.5 KiB
C++
60 lines
2.5 KiB
C++
// fig15_20.cpp
|
|
// Implementing customDistance using template metaprogramming.
|
|
#include <array>
|
|
#include <iostream>
|
|
#include <iterator>
|
|
#include <list>
|
|
#include <ranges>
|
|
#include <type_traits>
|
|
|
|
// calculate the distance (number of items) between two iterators;
|
|
// requires at least input iterators
|
|
template <std::input_iterator Iterator>
|
|
auto customDistance(Iterator begin, Iterator end) {
|
|
// for random-access iterators subtract the iterators
|
|
if constexpr (std::is_base_of_v<std::random_access_iterator_tag,
|
|
Iterator::iterator_category>) {
|
|
|
|
std::cout << "customDistance with random-access iterators\n";
|
|
return end - begin; // O(1) operation for random-access iterators
|
|
}
|
|
else { // for all other iterators
|
|
std::cout << "customDistance with non-random-access iterators\n";
|
|
std::ptrdiff_t count{0};
|
|
|
|
// increment from begin to end and count number of iterations;
|
|
// O(n) operation for non-random-access iterators
|
|
for (auto iter{begin}; iter != end; ++iter) {
|
|
++count;
|
|
}
|
|
|
|
return count;
|
|
}
|
|
}
|
|
|
|
int main() {
|
|
const std::array ints1{1, 2, 3, 4, 5}; // has random-access iterators
|
|
const std::list ints2{1, 2, 3}; // has bidirectional iterators
|
|
|
|
auto result1{customDistance(ints1.begin(), ints1.end())};
|
|
std::cout << "ints1 number of elements: " << result1 << "\n";
|
|
auto result2{customDistance(ints2.begin(), ints2.end())};
|
|
std::cout << "ints2 number of elements: " << result2 << "\n";
|
|
}
|
|
|
|
|
|
/**************************************************************************
|
|
* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
|
|
* Pearson Education, Inc. All Rights Reserved. *
|
|
* *
|
|
* DISCLAIMER: The authors and publisher of this book have used their *
|
|
* best efforts in preparing the book. These efforts include the *
|
|
* development, research, and testing of the theories and programs *
|
|
* to determine their effectiveness. The authors and publisher make *
|
|
* no warranty of any kind, expressed or implied, with regard to these *
|
|
* programs or to the documentation contained in these books. The authors *
|
|
* and publisher shall not be liable in any event for incidental or *
|
|
* consequential damages in connection with, or arising out of, the *
|
|
* furnishing, performance, or use of these programs. *
|
|
**************************************************************************/
|