This happens because there is no specialization for std::tr1::hash<Key> with Key = std::pair<int, int>. You must to specialize std::tr1::hash<Key> with Key = std::pair<int, int> before declaring tr1::unordered_map<Pair,bool> h;. This happens because std don’t know how to hash a pair<int, int>. Following there is a example of how to specialize std::tr1::hash<> template <> struct std::tr1::hash<std::pair<int, int> … Read more
I think the 2009 paper “Pairs do not make good ranges” by Alisdair Meredith is at least part of the answer. Basically, many algorithms return pairs of iterators that are actually not guaranteed to be valid ranges. It seems they removed the support for pair<iterator,iterator> from the for-range loop for this reason. However, the proposed … Read more
You can use the preprocessor “stringify” # to do what you want: #include <stdio.h> #define PRINTER(name) printer(#name, (name)) void printer(char *name, int value) { printf(“name: %s\tvalue: %d\n”, name, value); } int main (int argc, char* argv[]) { int foo = 0; int bar = 1; PRINTER(foo); PRINTER(bar); return 0; } name: foo value: 0 name: … Read more
std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via operator < (such as required by std::map). If you don’t write them you can’t make a mistake (remember how strict weak ordering … Read more
Tuples are available since .NET4.0 and support generics: Tuple<string, int> t = new Tuple<string, int>(“Hello”, 4); In previous versions you can use System.Collections.Generic.KeyValuePair<K, V> or a solution like the following: public class Pair<T, U> { public Pair() { } public Pair(T first, U second) { this.First = first; this.Second = second; } public T First … Read more
std::vector<std::pair<std::string, bool> > v; std::sort(v.begin(), v.end()); std::pair overloads operator< to sort first by the first element then by the second element. Thus, if you just sort the vector using the default sort ordering (operator<), you’ll get your desired ordering.
As of C++11, you have two major additional options. First, you can use insert() with list initialization syntax: function.insert({0, 42}); This is functionally equivalent to function.insert(std::map<int, int>::value_type(0, 42)); but much more concise and readable. As other answers have noted, this has several advantages over the other forms: The operator[] approach requires the mapped type to … Read more
What is the equivalent of the C++ Pair in Java?
You need world[src] since that is the name of your map variable, that should work.
You just: std::sort(v.begin(), v.end()); std::pair is lexicographically compared. On the other hand if you want to sort them with respect the second element of the std::pair then you would have to defind a custom comparator in the following manner: std::sort(v.begin(), v.end(), [](std::pair<int, std::string> const &p1, std::pair<int, std::string> const &p2) { return (p1.second == p2.second)? p1.first … Read more