Let's say that I've got a : #include <utility> using namespace std; typedef pair<int, int> my_pair; how do I initialize a const my_pair ?

2013年10月29日 · The primary usecase is for the return type of a function: C++ does not allow returning multiple values, but allows returning a structure with multiple fields. Rather than use output parameters, I prefer using a pair or tuple.

2008年9月18日 · std::pair is a data type for grouping two values together as a single object. std::map uses it for key, value pairs. While you're learning pair, you might check out tuple. It's like pair but for grouping an arbitrary number of values. tuple is part of TR1 and many compilers already include it with their Standard Library implementations.

2010年9月28日 · You could simplify your code by creating a helper function to create pairs of pairs, analog to the std::make_pair helper function that is available in the standard library.

:-) The string literals have a type const char[], the pair type has a member of type char*; the pair constructor cannot remove the const qualifier. That said; really: use std::string , using a pointer as a map key is almost always A Bad Idea.

2016年6月17日 · Fortunately, C++17 has a solution for exactly this problem, the structured binding declaration. Even the non-reference interface can be improved. auto[x, y, z] = g[i]; The above line declares x, y,z and initializes them with the values of g[i]. Not only is it cleaner, but it could be more efficient for types that are expensive to construct.

Unfortunately, this program has undefined behavior. C++11 §17.6.4.2.1: A program may add a template specialization for any standard library template to namespace std only if the declaration depends on a user-defined type and the specialization meets the standard library requirements for the original template and is not explicitly prohibited.

How to use pair correctly in C++. 9. std::pair assigning first and second to semantically named variables. 3.

I agree with @lukasl1991, this is a good idea. I made it independent of the arch size like this. It works efficiently for the common case where the ints (generally) fit in a short on 32 bit systems or in 4 bytes on systems where size_t is 8 bytes: code struct Pair_Hash { inline size_t operator() (const std::pair<int, int> &pair) const { return pair.first + (pair.second << (sizeof(size_t) * 8 / ...

2015年3月20日 · The usage of pair in C++. pair<some_datatype, some_other_datatype> my_pairs; The above line will make pairs of the first element with respect to the second element, now you can use this pair like this : pair<int,int> my_pairs; my_pairs = make_pair(5,6); cout<<my_pairs.first<<" "<<my_pairs.second<<endl;