range_by_example
range v3 example code
The intent of this project is to make example code for Eric Niebler's range v3 library. A host of basic information can be found on the range v3 github.
In general this code is written to c++17 so a modern C++ compiler is required. To date usage is primarily pre-release gcc-7.
Why Ranges?
Simpler more elegant code. Much detail in the standard library proposal.
Hello Ranges!
#include <range/v3/all.hpp> //get everything
namespace rng = ranges::v3; //easy access
#include <iostream>
#include <string>
using namespace std;
int main() {
string s { "hello" };
//output: h e l l o
rng::for_each( s, [](char c){ cout << c << " "; });
cout << endl;
}Example Conventions
In general examples will shorten code text by omitting includes and assuming the following:
#include <range/v3/all.hpp> //get everything
namespace rng = ranges::v3; //easy access
#include <...various std library headers...>
using namespace std;
Range Library Organization
The examples are largely divided into 2 main groups -- algorithms and views.
Algorithms
for_each
Applies a function to each element of the range.
/* output
vector: 1 2 3 4 5 6
array: 1 2 3 4 5 6
list: 1 2 3 4 5 6
fwd_list: 1 2 3 4 5 6
deque: 1 2 3 4 5 6
*/
#include <range/v3/algorithm/for_each.hpp> //specific includes
//...includes omitted...
auto print = [] (int i) { cout << i << " "; };
int main() {
cout << "vector: ";
vector<int> v { 1, 2, 3, 4, 5, 6 };
rng::for_each( v, print ); //1 2 3 4 5 6
cout << endl << "array: ";
array<int, 6> a { 1, 2, 3, 4, 5, 6 };
rng::for_each( a, print );
cout << endl << "list: ";
list<int> ll { 1, 2, 3, 4, 5, 6 };
rng::for_each( ll, print );
cout << endl << "fwd_list: ";
forward_list<int> fl { 1, 2, 3, 4, 5, 6 };
rng::for_each( fl, print );
cout << endl << "deque: ";
deque<int> d { 1, 2, 3, 4, 5, 6 };
rng::for_each( d, print );
cout << endl;
}all_of, any_of, none_of
Tests a predicate against each element of the range returning a bool result.
/* output
vector: 6 2 3 4 5 6
vector any is_six: true
vector all is_six: false
vector none of is_six: false
*/
#include <range/v3/algorithm/all_of.hpp> //specific includes
#include <range/v3/algorithm/any_of.hpp>
#include <range/v3/algorithm/none_of.hpp>
//...standard includes omitted...
int main() {
cout << "vector: ";
vector<int> v { 6, 2, 3, 4, 5, 6 };
//...printing vector omitted...
auto is_six = [](int i) -> bool { return i == 6; };
if (rng::any_of( v, is_six )) {
cout << "vector any is_six: true" << endl;
};
if (!rng::all_of( v, is_six )) {
cout << "vector all is_six: false" << endl;
};
if (!rng::none_of( v, is_six )) {
cout << "vector none of is_six: false" << endl;
};
}set_union, set_intersection
Computes the union or intersection of two sets (sorted ranges).
/* output
set s1: 1 2 3 4 5 7
set s2: 1 2 3 4 6 8
union: 1 2 3 4 5 6 7 8
intersection: 1 2 3 4
*/
#include <range/v3/algorithm/set_algorithm.hpp>
//...standard includes omitted...
namespace rng = ranges::v3; //easy access
void output(const vector<int>& range) {
for (auto i : range) {
cout << i << ' ';
}
cout << endl;
}
int main() {
vector<int> s1 = {1, 2, 3, 4, 5, 7};
cout << "set s1: ";
output(s1);
vector<int> s2 = {1, 2, 3, 4, 6, 8};
cout << "set s2: ";
output(s2);
{
vector<int> u;
auto it = rng::set_union(
s1.cbegin(), s1.cend(), s2.cbegin(), s2.cend(), rng::back_inserter(u));
cout << "union: ";
output(u);
}
{
vector<int> u;
auto it = rng::set_intersection(
s1.cbegin(), s1.cend(), s2.cbegin(), s2.cend(), rng::back_inserter(u));
cout << "intersection: ";
output(u);
}
}Views
drop, drop_exactly, drop_while
Lazily remove elements from the beginning of a range.
drop: Given a source range and an integral count, return a range consisting of all but the first count elements from the source range, or an empty range if it has fewer elements.
drop_exactly: Given a source range and an integral count, return a range consisting of all but the first count elements from the source range. The source range must have at least that many elements.
drop_while: Remove elements from the front of a range that satisfy a unary predicate.
/* output
vector: 6 2 3 4 5 6
vector drop half: 4 5 6
vector drop exactly one: 2 3 4 5 6
vector drop leading evens: 3 4 5 6
*/
int main() {
auto print = [](int i) { cout << i << " "; };
cout << "vector: ";
vector<int> v { 6, 2, 3, 4, 5, 6 };
rng::for_each(v, print);
cout << endl;
cout << "vector drop half: ";
auto last_half = rng::view::drop(v, v.size()/2);
rng::for_each(last_half, print);
cout << endl;
cout << "vector drop exactly one: ";
auto dropped_1 = rng::view::drop(v, 1);
rng::for_each(dropped_1, print);
cout << endl;
cout << "vector drop leading evens: ";
auto is_even = [](int i) { return i % 2 == 0; };
auto after_leading_evens = rng::view::drop_while(v, is_even);
rng::for_each(after_leading_evens, print);
cout << endl;
}stride
Lazily skip over elements in a range N elements per step.
Given a source range and an integral stride value, return a range consisting of every Nth element, starting with the first.
/* output
vector: 6 2 3 4 5 6
vector every 3rd value: 6 4
*/
int main() {
auto print = [](int i) { cout << i << " "; };
cout << "vector: ";
vector<int> v { 6, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0 };
rng::for_each(v, print);
cout << endl;
cout << "vector every 3rd value: ";
auto strided = rng::view::stride(v, 3);
rng::for_each(strided, print);
cout << endl;
}Range Composition
Ranges can be composed using the pipe (|) operator.
Values at even/odd indicies in a range
Values at even indicies can be viewed by using view::stride(2) to step (or stride) 2 indicies at a time. Like skipping a stairs when climbing stairs. To create a view of the values at odd indicies the first value in the source range must be dropped, then start striding.
/* output
vector: 6 2 3 4 5 6 7 8 9 1 0
vector values at even indicies: 6 3 5 7 9 0
vector values at odd indicies: 2 4 6 8 1
*/
int main() {
auto print = [](int i) { cout << i << " "; };
cout << "vector: ";
vector<int> v { 6, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0 };
rng::for_each(v, print);
cout << endl;
cout << "vector values at even indicies: ";
auto evens = rng::view::stride(v, 2);
rng::for_each(evens, print);
cout << endl;
cout << "vector values at odd indicies: ";
auto odds = rng::view::drop_exactly(v, 1) | rng::view::stride(2);
rng::for_each(odds, print);
cout << endl;
}