stl-algorithm

问题 The C++ standard library's max_element algorithm requires the iterators passed as inputs to model ForwardIterator . My understanding is that ForwardIterator refines InputIterator by specifying that you can use a ForwardIterator to iterate over the same range multiple times. Therefore, multi-pass algorithms require ForwardIterator s. However, max_element is not a multi-pass algorithm - it is sufficient to iterate over a range once to determine its maximum element. So why does max_element need

问题 The C++ standard library's max_element algorithm requires the iterators passed as inputs to model ForwardIterator . My understanding is that ForwardIterator refines InputIterator by specifying that you can use a ForwardIterator to iterate over the same range multiple times. Therefore, multi-pass algorithms require ForwardIterator s. However, max_element is not a multi-pass algorithm - it is sufficient to iterate over a range once to determine its maximum element. So why does max_element need

问题 I'm trying to code opposite action to this: std::ostream outs; // properly initialized of course std::set<int> my_set; // ditto outs << my_set.size(); std::copy( my_set.begin(), my_set.end(), std::ostream_iterator<int>( outs ) ); it should be something like this: std::istream ins; std::set<int>::size_type size; ins >> size; std::copy( std::istream_iterator<int>( ins ), std::istream_iterator<int>( ins ) ???, std::inserter( my_set, my_set.end() ) ); But I'm stuck with the 'end' iterator --

问题 When thinking about this question I start to wondering if std::copy() and/or std::fill are specialized (I really mean optimized) for std::vector<bool> . Is this required by C++ standard or, perhaps, it is common approach by C++ std library vendors? Simple speaking, I wonder to know if the following code: std::vector<bool> v(10, false); std::fill(v.begin(), v.end(), true); is in any way better/different than that: std::vector<bool> v(10, false); for (auto it = v.begin(); it != v.end(); ++it)

问题 I'm working on some code and I have a section where I do a one off sort function. To implement it I decided it was easiest to overload the operator< function. What I would prefer to do is move the implementation of the sort closer to the actual call by using some sort of boost::bind, boost::phoenix, lambda or some other type of implementation. Unfortunately I don't have access to new C++11 functionality. Below is some example code. // In a header struct foo { char * a; char * c_str() { return

问题 This question already has answers here : Nice way to append a vector to itself (4 answers) Closed 5 years ago . Inspired by this question, asking how to append a vector to itself, my first thought was the following (and yes, I realize insert is a better option now): #include <algorithm> #include <iostream> #include <iterator> #include <vector> int main() { std::vector<int> vec {1, 2, 3}; std::copy (std::begin (vec), std::end (vec), std::back_inserter (vec)); for (const auto &v : vec) std:

问题 I was looking at the various signatures for std::find_if on cppreference.com, and I noticed that the flavors that take a predicate function appear to accept it by value: template< class InputIt, class UnaryPredicate > InputIt find_if( InputIt first, InputIt last, UnaryPredicate p ); If I understand them correctly, lambdas with captured variables allocate storage for either references or copies of their data, and so presumably a "pass-by-value" would imply that the copies of captured data are

问题 This question already has answers here : Printing lists with commas C++ (27 answers) Closed 3 years ago . Is there a way to use a std::ostream_iterator (or similar) such that the delimiter isn't placed for the last element? #include <iterator> #include <vector> #include <algorithm> #include <string> using namespace std; int main(int argc, char *argv[]) { std::vector<int> ints = {10,20,30,40,50,60,70,80,90}; std::copy(ints.begin(),ints.end(),std::ostream_iterator<int>(std::cout, ",")); } Will

问题 Greetings, I am trying to perform a copy from one vector (vec1) to another vector (vec2) using the following 2 abbreviated lines of code (full test app follows): vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); While the call to vec2 sets the capacity of vector vec2, the copying of data to vec2 seems to not fill in the values from vec1 to vec2. Replacing the copy() function with calls to push_back() works as expected. What am I missing here? Thanks for your help.

问题 I have been trying to find the intersection between two std::set in C++, but I keep getting an error. I created a small sample test for this #include <iostream> #include <vector> #include <algorithm> #include <set> using namespace std; int main() { set<int> s1; set<int> s2; s1.insert(1); s1.insert(2); s1.insert(3); s1.insert(4); s2.insert(1); s2.insert(6); s2.insert(3); s2.insert(0); set_intersection(s1.begin(),s1.end(),s2.begin(),s2.end()); return 0; } The latter program does not generate