std-pair

问题 This question already has answers here : How do I sort a vector of pairs based on the second element of the pair? (7 answers) Closed 6 years ago . vector<pair<int,int> > v; for(i=0;i<5;i++){ cin>>b>>c; v.push_back(make_pair(b,c)); } sort(v.begin(),v.end()); Is it possible to write a comparator for the sort function such that v[i].first is sorted in increasing order and for similar values of v[i].first , v[i].second is sorted in decreasing order? like:- i/p: 13 10 44 15 13 15 13 99 6 45 o/p: 6

问题 This question already has answers here : How do I sort a vector of pairs based on the second element of the pair? (7 answers) Closed 6 years ago . vector<pair<int,int> > v; for(i=0;i<5;i++){ cin>>b>>c; v.push_back(make_pair(b,c)); } sort(v.begin(),v.end()); Is it possible to write a comparator for the sort function such that v[i].first is sorted in increasing order and for similar values of v[i].first , v[i].second is sorted in decreasing order? like:- i/p: 13 10 44 15 13 15 13 99 6 45 o/p: 6

问题 What is the C equivalent of std::pair from C++? I'm trying to find the equivalent on the web and can't find anything but explanations of what it does. 回答1: There isn't one. std::pair is a template, and C doesn't have anything similar to templates. For a given specialisation of the template, you can define a structure that's more or less equivalent; so that std::pair<int, double> is similar to struct pair_int_double { int first; double second; }; but you've chosen the wrong language if you

问题 What is the C equivalent of std::pair from C++? I'm trying to find the equivalent on the web and can't find anything but explanations of what it does. 回答1: There isn't one. std::pair is a template, and C doesn't have anything similar to templates. For a given specialisation of the template, you can define a structure that's more or less equivalent; so that std::pair<int, double> is similar to struct pair_int_double { int first; double second; }; but you've chosen the wrong language if you

问题 What is the C equivalent of std::pair from C++? I'm trying to find the equivalent on the web and can't find anything but explanations of what it does. 回答1: There isn't one. std::pair is a template, and C doesn't have anything similar to templates. For a given specialisation of the template, you can define a structure that's more or less equivalent; so that std::pair<int, double> is similar to struct pair_int_double { int first; double second; }; but you've chosen the wrong language if you

问题 int main() { pair<int, int> res; // check here pair is empty ? // res = make_pair(1 , 2); return 0; } In the above snippet what is the ideal way to check if a pair has been initilaized or not? EDIT: As pointed out in some answers below, using the word "uninitialized" is wrong here, to be more specific how do I check if the value has been explicitly set (other than the default constructor) 回答1: There's no such thing as unitialized std::pair . Default constructor for std::pair will value

问题 int main() { pair<int, int> res; // check here pair is empty ? // res = make_pair(1 , 2); return 0; } In the above snippet what is the ideal way to check if a pair has been initilaized or not? EDIT: As pointed out in some answers below, using the word "uninitialized" is wrong here, to be more specific how do I check if the value has been explicitly set (other than the default constructor) 回答1: There's no such thing as unitialized std::pair . Default constructor for std::pair will value

来源： https://stackoverflow.com/questions/64127498/automatic-conversion-from-derived-class-to-base-class-member-variables-type

问题 I have vector< pair<int, int>> myVec (N); I want to have all pairs initialized to -1,-1. 回答1: Here you go: #include <utility> vector<pair<int, int>> myVec (N, std::make_pair(-1, -1)); The second argument to that constructor is the initial value that the N pairs will take. 回答2: Just to add some additional info (not quite what the Asker wanted, but asked for in the comments of the accepted answer): Individual initialization can be done with (C++11): std::vector<std::pair<int, int> > vec1 = { {1

问题 #include <bits/stdc++.h> using namespace std; int main() { vector<pair<int,int>>v; v.push_back(make_pair(1,3)); v.push_back(make_pair(1,1)); v.push_back(make_pair(2,19)); v.push_back(make_pair(2,4)); int n = 4; stable_sort(v.begin(),v.end()); for (int i = 0; i < n; i++) cout << "[" << v[i].first << ", " << v[i].second << "] "; return 0; } Output : [1, 1] [1, 3] [2, 4] [2, 19] Expected Output : [1, 3] [1, 1] [2, 19] [2, 4] Why does the vector of pairs not maintain the relative ordering even