I posted this in the cpplang slack, and Casey Carter responded: The description of the algorithm in the standard is defective. The intent is to determine [if] every element in the needle appears in order in the haystack. [The algorithm it actually performs is:] “Returns true if the intersection of sorted sequences R1 and R2 … Read more
Compare it with the naive implementation: template< class InputIt, class Size, class OutputIt> OutputIt copy_n(InputIt first, Size count, OutputIt result) { for (Size i = 0; i < count; ++i) { *result++ = *first++; } return result; } This version does one more increment of first! count==0, both do 0 increments of first. count==1, their … Read more
If you are using C++0X you can use a simple lambda expression std::string username = “Nicholas”; std::find_if(userlist.begin(), userlist.end(), [username](Nick const& n){ return n.username == username; })
You’re right. You can use Boost.Range adaptors to achieve composition.
It’s explicitly forbidden by the C++98/03 standard. C++11 remove that restriction. To be more complete : The restrictions on types that are used as template parameters are listed in article 14.3.1 of the C++03 (and C++98) standard: A local type, a type with no linkage, an unnamed type or a type compounded from any of … Read more
std::random_shuffle may make use, under the hood, of random C family of functions. These functions use global state for seeds and other state. So it is being deprecated because shuffle will do the same, but better. Namely, it uses the new <random> header from C++11 that doesn’t use global state, but its own objects making … Read more
std::transform is the same as map. The idea is to apply a function to each element in between the two iterators and obtain a different container composed of elements resulting from the application of such a function. You may want to use it for, e.g., projecting an object’s data member into a new container. In … Read more
The standard library favours elementary algorithms. Containers and algorithms should be independent of each other if possible. Likewise, algorithms that can be composed of existing algorithms are only rarely included, as shorthand. If you require a transform if, you can trivially write it. If you want it /today/, composing of ready-mades and not incur overhead, … Read more
You haven’t provided an output iterator for set_intersection template <class InputIterator1, class InputIterator2, class OutputIterator> OutputIterator set_intersection ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result ); Fix this by doing something like …; set<int> intersect; set_intersection(s1.begin(), s1.end(), s2.begin(), s2.end(), std::inserter(intersect, intersect.begin())); You need a std::insert iterator since the set is as of … Read more
Let’s look at some permutations: 1 2 3 4 1 2 4 3 1 3 2 4 1 3 4 2 1 4 2 3 1 4 3 2 2 1 3 4 … How do we go from one permutation to the next? Firstly, let’s look at things a little differently. We can view … Read more