Standard Library Element-Wise Range Modifications Element-Modifying Algorithms Change
New to C++'s standard library algorithms? ⇒ Short Introduction
Filling / Overwriting Ranges Filling Ranges Fill
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> v {1,0,9,0,9,1,0,1};
fill(begin(v)+2, begin(v)+7, 2);
for (int x : v) { std::cout << x << ' '; } // 1 0 2 2 2 2 2 1
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> v {1,0,9,0,9,1,0,1};
fill_n(begin(v)+2, 5, 2);
for (int x : v) { std::cout << x << ' '; } // 1 0 2 2 2 2 2 1
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> v {9,0,9,1,0};
std::ranges::fill(v, 2);
for (int x : v) { std::cout << x << ' '; } // 2 2 2 2 2
std::cout << '\n';
}
Example: C++14-Lambda As Generator
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto gen = [i=0]() mutable { i += 2; return i; };
// init-^^^ ^^^^^^^⇒ member 'i' changeable!
std::cout << gen() << '\n'; // 2
std::cout << gen() << '\n'; // 4
std::cout << gen() << '\n'; // 6
}
Example: Generator Function Class
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
class int_range_generator {
int val_ = 0;
int step_ = 1;
public:
int_range_generator () = default;
explicit constexpr
int_range_generator (int start, int step=1) noexcept:
val_{start}, step_{step} {}
constexpr int operator () () noexcept {
int const old = val_;
val_ += step_;
return old;
}
};
auto gen = int_range_generator{2,2};
std::cout << gen() << '\n'; // 2
std::cout << gen() << '\n'; // 4
std::cout << gen() << '\n'; // 6
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto gen = [i=0]() mutable { i += 2; return i; };
std::vector<int> v;
v.resize(7,0);
generate(begin(v)+1, begin(v)+5, gen);
for (int x : v) { std::cout << x << ' '; } // 0 2 4 6 8 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto gen = [i=0]() mutable { i += 2; return i; };
std::vector<int> v;
v.resize(7,0);
generate_n(begin(v)+1, 4, gen);
for (int x : v) { std::cout << x << ' '; } // 0 2 4 6 8 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto gen = [i=0]() mutable { i += 2; return i; };
std::vector<int> v;
v.resize(4,0);
std::ranges::generate(v, gen);
for (int x : v) { std::cout << x << ' '; } // 2 4 6 8
std::cout << '\n';
}
This algorithm is also known as map
in other programming languages.
The output target must be able to receive as many elements as there are in the input range.
The function (object) f must not have side effects / be stateful
because the order in which it is applied to the input elements
is not guaranteed.
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
// f: 'x' → "<x>"
auto f = [](char c) { return std::string("<") + c + ">"; };
std::string in = "vwxyza";
std::vector<std::string> out;
// make sure 'out' can fit result
out.resize(4);
transform(begin(in)+1, begin(in)+5, begin(out), f);
for (auto const& x : out) { std::cout << x << ' '; } // <w> <x> <y> <z>
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
// f: 'y',3 → "yyy"
auto f = [](char c, int i) { return std::string(i,c); };
std::string in1 = "wxy";
std::vector<int> in2 = {1,2,3};
std::vector<std::string> out;
// make sure 'out' can fit result
out.resize(3);
transform(begin(in1), end(in1), begin(in2), begin(out), f);
for (auto const& x : out) { std::cout << x << ' '; } // w xx yyy
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
// f: 'x' → "<x>"
auto f = [](char c) { return std::string("<") + c + ">"; };
std::string in = "wxyz";
std::vector<std::string> out;
// make sure 'out' can fit result
out.resize(4);
std::ranges::transform(in, begin(out), f);
for (auto const& x : out) { std::cout << x << ' '; } // <w> <x> <y> <z>
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
// f: 'y',3 → "yyy"
auto f = [](char c, int i) { return std::string(i,c); };
std::string in1 = "wxyz";
std::vector<int> in2 = {1,2,3};
std::vector<std::string> out;
// make sure 'out' can fit result
out.resize(3);
std::ranges::transform(in1, in2, begin(out), f);
for (auto const& x : out) { std::cout << x << ' '; } // w xx yyy
std::cout << '\n';
}
replace / replace_if
replace_if
replace
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> v {1,2,3,2,4,2,2,6};
replace(begin(v)+2, begin(v)+7, 2, 0);
for (int x : v) { std::cout << x << ' '; } // 1 2 3 0 4 0 0 6
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> v {3,2,4,2,2};
std::ranges::replace(v, 2, 0);
for (int x : v) { std::cout << x << ' '; } // 3 0 4 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto const is_even = [](int x) { return !(x & 1); };
std::vector<int> v {1,2,3,2,5,2,2,6,7};
replace_if (begin(v)+2, begin(v)+7, is_even, 0);
for (int x : v) { std::cout << x << ' '; } // 1 2 3 0 5 0 0 6 7
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto const is_even = [](int x) { return !(x & 1); };
std::vector<int> v {3,2,5,4,6};
std::ranges::replace_if (v, is_even, 0);
for (int x : v) { std::cout << x << ' '; } // 3 0 5 0 0
std::cout << '\n';
}
replace_copy / replace_copy_if
replace_copy/_copy_if
replace_copy
The output target must be able to receive as many elements as there are in the input range.
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> in {1,2,3,2,4,2,2,6,7};
std::vector<int> out;
out.resize(5);
replace_copy(begin(in)+2, begin(in)+7, begin(out), 2, 0);
for (int x : out) { std::cout << x << ' '; } // 3 0 4 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
std::vector<int> in {3,2,4,2,2};
std::vector<int> out;
out.resize(5);
std::ranges::replace_copy(in, begin(out), 2, 0);
for (int x : out) { std::cout << x << ' '; } // 3 0 4 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto const is_even = [](int x) { return !(x & 1); };
std::vector<int> in {2,3,2,5,4,6,6};
std::vector<int> out;
out.resize(5);
replace_copy_if (begin(in)+1, begin(in)+7, begin(out), is_even, 0);
for (int x : out) { std::cout << x << ' '; } // 3 0 5 0 0
std::cout << '\n';
}
#include <vector>
#include <iostream>
#include <algorithm>
int main () {
auto const is_even = [](int x) { return !(x & 1); };
std::vector<int> in {3,2,5,4,6};
std::vector<int> out;
out.resize(5);
std::ranges::replace_copy_if (in, begin(out), is_even, 0);
for (int x : out) { std::cout << x << ' '; } // 3 0 5 0 0
std::cout << '\n';
}
Comments…