here<\/a>. It works will Clang 3.6.2 or later, gcc 5.2 or later, and VC++ 15.9 or later. The code samples below were written and tested with the latter. On a side note, these samples represent typical implementations and not necessarily the only solutions one could think of.<\/p>\n\n\n\nAlthough the standard namespace for the Ranges library is std::ranges<\/tt>, in this current implementation of the library it is ranges::v3<\/tt>.<\/p>\n\n\n\n
The following namespace aliases are used in the samples below:<\/p>\n\n\n\n
namespace rs = ranges::v3;\nnamespace rv = ranges::v3::view;\nnamespace ra = ranges::v3::action;<\/pre>\n\n\n\nAlso, for simplicity, we will refer to the following object, function, and lambda functions:<\/p>\n\n\n\n
std::string to_roman(int value)\n{\n std::vector<std::pair<int, char const*>> roman\n {\n { 1000, \"M\" },{ 900, \"CM\" },\n { 500, \"D\" },{ 400, \"CD\" },\n { 100, \"C\" },{ 90, \"XC\" },\n { 50, \"L\" },{ 40, \"XL\" },\n { 10, \"X\" },{ 9, \"IX\" },\n { 5, \"V\" },{ 4, \"IV\" },\n { 1, \"I\" }\n };\n\n std::string result;\n for (auto const & [d, r]: roman)\n {\n while (value >= d)\n {\n result += r;\n value -= d;\n }\n }\n\n return result;\n}\n\nstd::vector<int> v{1,1,2,3,5,8,13,21,34};\n\nauto print_elem = [](auto const e) {std::cout << e << '\\n'; };\n\nauto is_even = [](auto const i) {return i % 2 == 0; };<\/pre>\n\n\n\nUPDATE<\/h4>I would like to thank Eric Niebler<\/strong> and all the others that commented below with suggestions for these code samples. I have updated a few based on their feedback.<\/p><\/div><\/div>\n\n\n\n\ud83d\udc49 Print the all the elements of a range<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::for_each(\n std::cbegin(v), std::cend(v), \n print_elem);\n\n\/\/ or \n \nfor(auto const i : v) \n{\n print_elem(i); \n};<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
rs::for_each(\n std::cbegin(v), std::cend(v), \n print_elem);\n\n\/\/ or\n\nrs::for_each(std::as_const(v), print_elem);<\/pre>\n\n\n\n\ud83d\udc49 Print all the elements of a range in reverse order<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::for_each(\n std::crbegin(v), std::crend(v),\n print_elem);<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
rs::for_each(\n std::crbegin(v), std::crend(v),\n print_elem);\n\n\/\/ or\n\nfor (auto const i : v | rv::reverse)\n{\n print_elem(i);\n};<\/pre>\n\n\n\n\ud83d\udc49 Print only the even elements of the range but in reverse order<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::for_each(\n std::crbegin(v), std::crend(v),\n [print_elem](auto const i) {\n if(i % 2 == 0)\n print_elem(i); \n });<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
for (auto const i : v \n | rv::reverse \n | rv::filter(is_even))\n{\n print_elem(i);\n};<\/pre>\n\n\n\n\ud83d\udc49 Skip the first two elements of the range and print only the even numbers of the next three in the range<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
auto it = std::cbegin(v);\nstd::advance(it, 2);\nauto ix = 0;\nwhile (it != std::cend(v) && ix++ < 3)\n{\n if (is_even(*it))\n print_elem(*it);\n it++;\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
for (auto const i : v \n | rv::drop(2)\n | rv::take(3)\n | rv::filter(is_even))\n{\n print_elem(i);\n};<\/pre>\n\n\n\n\ud83d\udc49 Print all numbers from 101 to 200<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
for (int n = 101; n <= 200; ++n)\n{\n print_elem(n);\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
for (auto n : rs::iota_view(101, 201))\n{\n print_elem(n);\n}<\/pre>\n\n\n\n\ud83d\udc49 Print all the Roman numerals from 101 to 200<\/h3>\n\n\n\n To convert a number to its corresponding Roman numeral the function to_roman()<\/tt> shown ealier is used.<\/p>\n\n\n\n
Before ranges:<\/p>\n\n\n\n
for (int i = 101; i <= 200; ++i)\n{\n print_elem(to_roman(i));\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
for (auto n : rs::iota_view(101, 201) \n | rv::transform(to_roman))\n{\n print_elem(n);\n}\n\n\/\/ or\n\nrs::for_each(rv::iota(101, 201), \n print_element, to_roman);<\/pre>\n\n\n\n\ud83d\udc49 Print the <\/strong>Roman numeral of the last three numbers divisible to 7 in the range [101, 200], in reverse order<\/strong><\/h3>\n\n\n\nBefore ranges:<\/p>\n\n\n\n
for (int n = 200, count=0; n >= 101 && count < 3; --n)\n{\n if (n % 7 == 0)\n {\n print_elem(to_roman(n));\n count++;\n }\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
for (auto n : rs::iota_view(101, 201) \n | rv::reverse\n | rv::filter([](auto v) {\n return v % 7 == 0; })\n | rv::transform(to_roman)\n | rv::take(3))\n{\n print_elem(n);\n}<\/pre>\n\n\n\n\ud83d\udc49 Create a range of strings containing the Roman numeral of the last three numbers divisible to 7 in the range [101, 200], in reverse order<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::vector<std::string> v;\nfor (int n = 200, count = 0; \n n >= 101 && count < 3; --n)\n{\n if (n % 7 == 0)\n {\n v.push_back(to_roman(n));\n count++;\n }\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
auto v = rs::iota_view(101, 201)\n | rv::reverse\n | rv::filter([](auto v) {return v % 7 == 0; })\n | rv::transform(to_roman)\n | rv::take(3)\n | rs::to_vector;<\/pre>\n\n\n\n\ud83d\udc49 Modify an unsorted range so that it retains only the unique values but in reverse order<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::vector<int> v{ 21, 1, 3, 8, 13, 1, 5, 2 };\n\nstd::sort(std::begin(v), std::end(v));\nv.erase(\n std::unique(std::begin(v), std::end(v)), \n std::end(v));\nstd::reverse(std::begin(v), std::end(v));<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
std::vector<int> v{ 21, 1, 3, 8, 13, 1, 5, 2 };\n\nv = std::move(v) | \n ra::sort | \n ra::unique | \n ra::reverse;<\/pre>\n\n\n\n\ud83d\udc49 Remove the smallest two and the largest two values of a range and retain the other ones, ordered, in a second range<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::vector<int> v{ 21, 1, 3, 8, 13, 1, 5, 2 };\nstd::vector<int> v2 = v;\nstd::sort(std::begin(v2), std::end(v2));\n \nauto first = std::begin(v2);\nstd::advance(first, 2);\nauto last = first;\nstd::advance(last, std::size(v2) - 4);\n\nv2.erase(last, std::end(v2));\nv2.erase(std::begin(v2), first);<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
std::vector<int> v{ 21, 1, 3, 8, 13, 1, 5, 2 };\nauto v2 = v | \n rs::copy | \n ra::sort | \n ra::slice(2, rs::end - 2);<\/pre>\n\n\n\n\ud83d\udc49 Concatenate all the strings in a given range into a single value<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
std::vector<std::string> words {\n \"Lorem\", \" \", \"ipsum\", \" \", \n \"dolor\", \" \", \"sit\", \" \", \n \"amet\"};\n\nstd::string text;\nfor (auto const & word : words)\n text += word;<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
std::vector<std::string> words {\n \"Lorem\", \" \", \"ipsum\", \" \", \n \"dolor\", \" \", \"sit\", \" \", \n \"amet\"};\n\nstd::string text = words | \n rs::move | \n ra::join;<\/pre>\n\n\n\n\ud83d\udc49 Count the number of words (as delimited by space) in a text<\/h3>\n\n\n\n Before ranges:<\/p>\n\n\n\n
auto text = \"Lorem ipsum dolor sit amet\";\n\nstd::istringstream iss(text);\nstd::vector<std::string> words(\n std::istream_iterator<std::string>{iss},\n std::istream_iterator<std::string>());\nauto count = words.size();\n\n\n\/\/ or\n\nsize_t count = 0;\nstd::vector<std::string> words;\nstd::string token;\nstd::istringstream tokenStream(text);\nwhile (std::getline(tokenStream, token, ' '))\n{\n ++count;\n}<\/pre>\n\n\n\nAfter ranges:<\/p>\n\n\n\n
auto text = \"Lorem ipsum dolor sit amet\";\n\nauto count = rs::distance(\n rv::c_str(text) | rv::split(' '));<\/pre>\n","protected":false},"excerpt":{"rendered":"The Ranges library proposal has been accepted for C++20 at the San Diego meeting of the standard committee in November last year. The library provides components for handling ranges of values aimed at simplifying our code. Unfortunately, the Ranges library is not very well documented, which makes it harder to grasp for those that want to learn it. This post is intended as an introduction based on examples of code written with and without Ranges.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7],"tags":[451,543,138,579],"class_list":["post-3325","post","type-post","status-publish","format-standard","hentry","category-c","tag-c","tag-c20","tag-library","tag-ranges"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t