std-pair

问题 I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this: void mappedWordsListSorter(){ for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){ vectorWordsList.push_back(*itr); } sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;}); } I need to find a way to do this without using a raw loop, using

问题 Sorry for a little bit beginner question. There are vector and vector of pairs typedef std::vector <int> TItems; typedef std::vector < std::pair <int, int> > TPairs; Is there any way to transform all first items in pair to another vector in one step int main () { TItems items; TPairs pairs; pairs.push_back (std::make_pair(1,3)); pairs.push_back (std::make_pair(5,7)); std::transform( items.begin(), items.end(), items.begin(), comp ( &pairs ) ); return 0; } How to design a functor? class comp {

问题 Does anyone know if there's a de-facto standard (i.e., TR1 or Boost) C++ function object for accessing the elements of a std::pair? Twice in the past 24 hours I've wished I had something like the keys function for Perl hashes. For example, it would be nice to run std::transform on a std::map object and dump all the keys (or values) to another container. I could certainly write such a function object but I'd prefer to reuse something that's had a lot of eyeballs on it. 回答1: boost::bind is what

问题 Does anyone know if there's a de-facto standard (i.e., TR1 or Boost) C++ function object for accessing the elements of a std::pair? Twice in the past 24 hours I've wished I had something like the keys function for Perl hashes. For example, it would be nice to run std::transform on a std::map object and dump all the keys (or values) to another container. I could certainly write such a function object but I'd prefer to reuse something that's had a lot of eyeballs on it. 回答1: boost::bind is what

问题 In an ACM example, I had to build a big table for dynamic programming. I had to store two integers in each cell, so I decided to go for a std::pair<int, int> . However, allocating a huge array of them took 1.5 seconds: std::pair<int, int> table[1001][1001]; Afterwards, I have changed this code to struct Cell { int first; int second; } Cell table[1001][1001]; and the allocation took 0 seconds. What explains this huge difference in time? 回答1: std::pair<int, int>::pair() constructor initializes

问题 This question already has answers here : Sorting a std::vector<std::pair<std::string,bool>> by the string? (4 answers) Closed 6 years ago . If I have a vector<pair<int,int> > datatype, what is the accepted way to sort it by the first element of the pair and then by second if the firsts are equal? For instance maybe (1,10), (3,3), (7,13), (7,16), (8,1), (8,2), (15,2) etc. 回答1: pair s by default compare by first element, then second. So, if you don't care about preserving the order when the

问题 I'm writing a pair wrapper. For the purposes of this question it can be simplified down to: using namespace std; template <class T1, class T2> class myPair { pair<T1, T2> member; public: myPair() = default; myPair(T1 x, T2 y) : member(make_pair(x, y)) {} }; I'd like to be able to treat a myPair as an index-able container of size 2. To do this I'd obviously need to write an index operator for myPair . I'd like to do something like this, but my return type will depend upon a method parameter,

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . I'm looking for a lib that would implement something similar to std::map and multimap, but without tree but vectors instead, like a pair<vector<key>,vector<value>> . The lib would have to keep the vectors synchronized and sorted. I'd like to compare the performance of maps, vector<pair<key,value>> and such a lib

问题 Is it possible for a multimap to contain within it pairs? IE, rather then being defined as multimap<char,int> for instance, it would be defined as multimap<pair, pair >? How would this multimap then be sorted? Also, how would one access the individual contents of each pair? 回答1: Is it possible for a multimap to contain within it pairs? Yes its possible. How would this multimap then be sorted? By the key/first pair (ie, first by the first element of the first pair, then by the second element

问题 I am having problem in writing copy constructor for pointers to objects. This is my exact problem I have a class G1 that has an object s1 as its private data member. This is an object of a struct. The struct is composed of a vector<pair<int,pointer to another object of a different class>>. Now when I create a pointer for G1 everything is fine. When I try to copy this pointer to another new pointer of the same class it is making a shallow copy. So when I try to delete the first pointer the