c-resources/CPlusPlus20ForProgrammers-m.../examples/ch14/fig14_18.cpp

90 lines
3.4 KiB
C++

// fig14_18.cpp
// Working with C++20 std::views.
#include <algorithm>
#include <iostream>
#include <iterator>
#include <map>
#include <ranges>
#include <string>
#include <vector>
int main() {
std::ostream_iterator<int> output{std::cout, " "};
auto isEven{[](int x) {return x % 2 == 0;}}; // true if x is even
// infinite view of even integers starting at 0
auto evens{std::views::iota(0) | std::views::filter(isEven)};
std::cout << "First five even ints: ";
std::ranges::copy(evens | std::views::take(5), output);
std::cout << "\nEven ints less than 12: ";
auto lessThan12{
evens | std::views::take_while([](int x) {return x < 12;})};
std::ranges::copy(lessThan12, output);
std::cout << "\nEven ints less than 12 reversed: ";
std::ranges::copy(lessThan12 | std::views::reverse, output);
std::cout << "\nSquares of even ints less than 12 reversed: ";
std::ranges::copy(
lessThan12
| std::views::reverse
| std::views::transform([](int x) {return x * x;}),
output);
std::cout << "\nSkip 1000 even ints, then take five: ";
std::ranges::copy(
evens | std::views::drop(1000) | std::views::take(5),
output);
std::cout << "\nFirst five even ints greater than 1000: ";
std::ranges::copy(
evens
| std::views::drop_while([](int x) {return x <= 1000;})
| std::views::take(5),
output);
// allow std::string object literals
using namespace std::string_literals;
std::map<std::string, int> romanNumerals{
{"I"s, 1}, {"II"s, 2}, {"III"s, 3}, {"IV"s, 4}, {"V"s, 5}};
auto displayPair{[](const auto& p) {
std::cout << p.first << " = " << p.second << "\n"; }};
std::cout << "\n\nromanNumerals:\n";
std::ranges::for_each(romanNumerals, displayPair);
std::ostream_iterator<std::string> stringOutput{std::cout, " "};
std::cout << "\nKeys in romanNumerals: ";
std::ranges::copy(romanNumerals | std::views::keys, stringOutput);
std::cout << "\nValues in romanNumerals: ";
std::ranges::copy(romanNumerals | std::views::values, output);
std::cout << "\nKeys in romanNumerals via std::views::elements: ";
std::ranges::copy(
romanNumerals | std::views::elements<0>, stringOutput);
std::cout << "\nvalues in romanNumerals via std::views::elements: ";
std::ranges::copy(romanNumerals | std::views::elements<1>, output);
std::cout << "\n";
}
/**************************************************************************
* (C) Copyright 1992-2021 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. *
**************************************************************************/