Modernes C++ programmieren

// https://godbolt.org/z/vW4xsMPq7
using std::pair; using std::make_pair;
namespace literal_p { // better to put user-defined literals in a namespace
constexpr pair<char,char> operator "" _p(const char* s, size_t len) {
    return len>=2 ? make_pair(s[0], s[1]) : make_pair( '-', '-' );
} }
struct Q {
    char a_; int n_;
    Q(char a, int n) : a_{a}, n_{n} {}
    operator pair<const char,int>() { return make_pair(a_, n_); }
};
// …
// explicit pairs:
map<int,int> nums { pair<int,int>(3,4), make_pair(7,8), make_pair(11,23) };
map nums2 { pair<int,int>(6,1), make_pair(5,2) };
// implicit pairs from initializer lists:
map<int,char> numch{{1,'a'},{2,'b'},{3,'c'}};
map<int,int> nums3 { {7,2}, {9,4} };
using namespace literal_p;
map<char,char> pmap { "ab"_p, "cd"_p, "ef"_p }; // detour via custom literal
cout <<= pmap;                                  // Output: a:b c:d e:f
map<char,int> qmap{Q('a',1),Q('b',2),Q('c',3)}; // implicit conversions
cout <<= qmap;                                  // Output: a:1 b:2 c:3