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You cannot register links. References are just aliases to help other variables.
map , string> m;
The reason your company is getting this particular error is because somewhere on the map, they are picking opssetting for mapped_type
, which in your case is string &
. One of the surgical interventions that (as in the []
operator) is able to return a link to mapped_type
:
mapped_type & operator [] (const key_type &)
string && operator [] (const key_type & _Keyval)
Standard 8.3.4:
There should be a few more links, no links, no linked tables, and no link references.
On the right, I recommend that you take advantage of the typedef
to make the code easier to read:
int main (){ typedef pair StringPair; typedef map StringPairMap; Test; StringPair p ("Fu", "Bar"); StringPairMap m; m [make_pair ("aa", "bb")] implies checking; Returns 0;
answered Jul 20 ’09 at 18:33
465k
Previous answers prevail here. Today we have std :: reference_wrapper
as part of the C ++ 11 standard:
#include #include #include Using the std namespace;int main () Test; A pair of lines p matches a pair of ("Foo", "Bar"); map , reference_wrapper > m; m [make_pair ("aa", "bb")] = test; Income 0;
std :: reference_wrapper is implicitly converted to a full reference to its internal type, but the following does not work in some contexts. In this case, call .get ()
to access it.
answered Jul 13 13 at 5:25 am
8,543
With boost :: reference_wrapper you can store private links in STL containers. Here’s your situation changed essentially (untested and certainly not surprisingly well written, just illustrates the point)
#include #include #include #include int main () typedef std :: pair PairType; typedef std :: map boost :: reference_wrapper MapType; std :: string verify = "Hello !!"; Card type m; PairType pp implies std :: make_pair ("aa", "bb"); m.insert (std :: make_pair (pp, boost :: ref (test))); MapType :: iterator it (m.find (pp)); if (what! = l. end ()) std :: cout << it-> second.get () << std :: endl; // change the test test = "I'm different now"; std :: cout << it-> second.get () << std :: endl; Returns 0;
answered Jul 21, 2009 at 15:06
1.548
You cannot use references as a value to guarantee the actual structure of the model... You can use pointers instead.
answered Jul 20 '09 here at 18:34
1.594
Basically, the point is that you can use links in containers. Of course, IF you start to properly prepare your class AND your container, you can. I copy it with the following two simple vector dishes: vectoref
, which modifies std :: vector <>
, and the similar vec
used. the scratch is realized.
#include #include // requires compilation with --std = c ++ 11 (at least)Using the std namespace;Class A int _a; // this is our real data A * _p; // to "trick" the compiler publicly: A (interval m = 0): _p (0) _a (n), cout << "Constructor (" << such << "," << _a << ") n"; // constructor used by the corresponding initializer_list (trick the compiler) A (const A & r): _p (const_cast (& r)) cout << "Copy constructor (" << this approach << "<-" << & r << ") n"; unnecessary print () const cout << "Practical example:" << this << "," << _a << " n"; ~ A () cout << "A (" << this << "," << _a << ") Destructor. N"; // just to know what is being copied implicitly Operator A & = (const A & r) cout << "Copied instance (" << this << "," << _a << ") n"; _a = r._a; _p means r._p; return * this; // just in case your company wants to check if a copy is organic, natural or fake bool is_fake () const return _p! = 0; A * ptr () const return _p;;Model class vec // vector class with initializer_list of links A !! publicly: const T * a [sz]; // put as pointer, get as links // because assigning to a link triggers a call to the copy operator int heart; vec (): cur (0) vec (std :: initializer_list l): cur (0) cout << "create with init list. n"; (auto & for w not: l) // wait for fake items a [cur ++] = t.ptr (); const T & operator [] I (int) return * a [i]; // expects clean items vec & push_back (const T & r) in [cur ++] implies & r; return * this; void copy_from (vec && r) for I (int means 0; i class vectoref:public vector // indistinguishable from vec, but extends std :: vector <> Choice size_type = typename vector :: size_type; publicly: Vector ref () vector (std :: initializer_list l) cout << "build from initialization list. n"; only for (auto & t: l) // wait for elements artificial vector :: push_back (t.ptr ()); const T & operator [] (size_type i) return * vector :: at (i); // expects clean items vector & T & push_back (const r) vector :: push_back (& r); undo * this; void copy_from (const vectoref && r) defined for (size_type i = 0; i :: push_back (r [i]); ;Class X // user connected to initializer_list publicly: X () void f (initializer_list l) const cout << "In f (...): n"; for (auto and from a to l) A. ptr () -> print (); ;int main () Aa (7), b (24), c (80); cout << "---------------------------------- n"; Control vector wa, a, b, c; // use the following line as an alternative // vec wa, a, b, c; // 5th undefined element w [0] .print (); w [3] .print (); cout << "---------------------------------- n"; Xx; x.f (a, b, c, a, b, c, b, a); cost << "===================================== n"; Returns 0;
answered Dec 10 '17 at 17:31
59
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Bugfixes Und Probleme Beim Erstellen Von Zeigern Auf Die Referenzauswahl Nt &
Correzioni Di Bug E Complicazioni Durante La Creazione Di Puntatori All'opzione Di Riferimento Nt &
Bugfixes En Daardoor Fouten Bij Het Maken Van Verwijzingen Naar Het Referentieassortiment Nt &
Correction De Bugs Et Inconvénients Lors De La Création De Pointeurs Vers Le Pointage De Référence Dans Nt &
참조 유형 Nt &
Исправлены ошибки и ошибки, при которых создавались указатели на ссылочный тип Nt &
Felkorrigeringar Och Fel Vid Konstruktion Av Pekare Till Referenstypen Nt &
Correções De Bugs E Erros No Caso De Criação De Ponteiros Para O Tipo De Referência Nt &
Obróbki Błędów I Błędy Podczas Tworzenia Wskaźników Do Tego Typu Referencji Nt &
Correcciones De Errores Y Errores Al Crear Punteros Al Tipo De Referencia Nt &