c-resources/CPlusPlus20ForProgrammers-m.../examples/ch15/fig15_08.cpp

57 lines
2.4 KiB
C++

// fig15_08.cpp
// Using concepts to select overloads.
#include <array>
#include <iostream>
#include <iterator>
#include <list>
// calculate the distance (number of items) between two iterators
// using input iterators; requires incrementing between iterators,
// so this is an O(n) operation
template <std::input_iterator Iterator>
auto customDistance(Iterator begin, Iterator end) {
std::cout << "Called customDistance with input iterators\n";
std::ptrdiff_t count{0};
// increment from begin to end and count number of iterations
for (auto& iter{begin}; iter != end; ++iter) {
++count;
}
return count;
}
// calculate the distance (number of items) between two iterators
// using random-access iterators and an O(1) operation
template <std::random_access_iterator Iterator>
auto customDistance(Iterator begin, Iterator end) {
std::cout << "Called customDistance with random-access iterators\n";
return end - begin; // returns a std::ptrdiff_t value
}
int main() {
std::array ints1{1, 2, 3, 4, 5}; // has random-access iterators
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";
}
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