std::bind
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| Definido no cabeçalho <functional>
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template< class F, class... Args > /*unspecified*/ bind( F&& f, Args&&... args ); |
(1) | (desde C++11) |
template< class R, class F, class... Args > /*unspecified*/ bind( F&& f, Args&&... args ); |
(2) | (desde C++11) |
O modelo
bind função gera um invólucro de encaminhamento de chamadas para f. Chamar esse envoltório é equivalente a chamar f com alguns de seus argumentos vinculados a args. Original:
The function template
bind generates a forwarding call wrapper for f. Calling this wrapper is equivalent to invoking f with some of its arguments bound to args. The text has been machine-translated via Google Translate.
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Internamente, o invólucro contém um objeto membro da
std::decay<F>::type tipo construído a partir de std::forward<F>(f), e um objeto por cada um dos args..., de std::decay<Arg_i>::type tipo, da mesma forma construído a partir de std::forward<Arg_i>(arg_i).Original:
Internally, the wrapper holds a member object of type
std::decay<F>::type constructed from std::forward<F>(f), and one object per each of args..., of type std::decay<Arg_i>::type, similarly constructed from std::forward<Arg_i>(arg_i).The text has been machine-translated via Google Translate.
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Parâmetros
| f | - | invocável objeto (objeto de função, o ponteiro para a função, a referência a função, o ponteiro para função de membro, ou ponteiro para dados de membro), que será obrigado a alguns argumentos
Original: invocable object (function object, pointer to function, reference to function, pointer to member function, or pointer to member data) that will be bound to some arguments The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| args | - | lista de argumentos para vincular, com os argumentos não ligados substituído pelo
_1, _2, _3... espaços reservados Original: list of arguments to bind, with the unbound arguments replaced by the placeholders _1, _2, _3... The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
Valor de retorno
Um objeto da função
T tipo não especificado, para o qual std::is_bind_expression<T>::value == true, e que pode ser armazenada em std::function. O objecto é móvel e se f todos args são móveis e, em caso contrário é copiável. O tipo define os seguintes membros:Original:
A function object of unspecified type
T, for which std::is_bind_expression<T>::value == true, and which can be stored in std::function. The object is movable if f and all args are movable, and is copyable otherwise. The type defines the following members:The text has been machine-translated via Google Translate.
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std :: bindOriginal:std::bindThe text has been machine-translated via Google Translate.
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Original:
std::bind
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Member type result_type
1) If F is a pointer to function or a pointer to member function, result_type is the return type of F. If F is a class type with nested typedef result_type, then result_type is F::result_type. Otherwise no result_type is defined.
2) result_type is exactly R.
Member function operator()
Given an object g obtained from an earlier call to bind, when it is invoked in a function call expression g(u1, u2, ... uM), an invocation of the stored object of type std::decay<F>::type takes place, with arguments defined as follows:
- If the argument is of type
std::reference_wrapper<T>(e.g. std::ref or std::cref) was used in the initial call tobind, then the referenceT&stored in the bound argument is passed to the invocable object. - If
std::is_bind_expression<T>::value == true(i.e. anothersbindsubexpression was used as an argument in the initial call tobind), then that bind-subexpressin is invoked immediately and its result is passed to the invocable object. If the bind subexpression has any placeholder arguments, they are picked fromu1, u2, .... - If
std::is_placeholder<T>::value != 0(i.e.,_1, _2, _3, ...was used as the argument to the initial call tobind), then the argument indicated by the placeholder (u1for_1,u2for_2, etc) is passed to the invocable object asstd::forward<Uj>(uj). - Otherwise, the stored argument is passed to the invocable object as-is.
If some of the arguments that are supplied in the call to g() are not matched by any placeholders stored in g, the unused arguments are evaluated and discarded.
Exceções
Só se a construção de lança
std::decay<F>::type std::forward<F>(f) de lança, ou qualquer um dos construtores para std::decay<Arg_i>::type do std::forward<Arg_i>(arg_i) corrsponding lança onde Arg_i é o tipo de ordem i e arg_i é o i-ésimo argumento em Args... args.Original:
Only throws if construction of
std::decay<F>::type from std::forward<F>(f) throws, or any of the constructors for std::decay<Arg_i>::type from the corrsponding std::forward<Arg_i>(arg_i) throws where Arg_i is the ith type and arg_i is the ith argument in Args... args.The text has been machine-translated via Google Translate.
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Notas
Os argumentos para se ligam são copiados ou movidos, e nunca são passados por referência a menos envolto em std::ref ou std::cref.
Original:
The arguments to bind are copied or moved, and are never passed by reference unless wrapped in std::ref or std::cref.
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Duplicar espaços reservados na expressão ligam mesmo (múltipla
_1, por exemplo) são permitidos, mas os resultados só são bem definido se o argumento correspondente (u1) é um rvalue lvalue ou não-móvel.Original:
Duplicate placeholders in the same bind expression (multiple
_1's for example) are allowed, but the results are only well defined if the corresponding argument (u1) is an lvalue or non-movable rvalue.The text has been machine-translated via Google Translate.
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Exemplo
#include <random>
#include <iostream>
#include <functional>
void f(int n1, int n2, int n3, const int& n4, int n5)
{
std::cout << n1 << ' ' << n2 << ' ' << n3 << ' ' << n4 << ' ' << n5 << '\n';
}
int g(int n1)
{
return n1;
}
struct Foo {
void print_sum(int n1, int n2)
{
std::cout << n1+n2 << '\n';
}
int data = 10;
};
int main()
{
using namespace std::placeholders;
// demonstrates argument reordering and pass-by-reference
int n = 7;
auto f1 = std::bind(f, _2, _1, 42, std::cref(n), n);
n = 10;
f1(1, 2, 1001); // 1 is bound by _1, 2 is bound by _2, 1001 is unused
// nested bind subexpressions share the placeholders
auto f2 = std::bind(f, _3, std::bind(g, _3), _3, 4, 5);
f2(10, 11, 12);
// common use case: binding a RNG with a distribution
std::default_random_engine e;
std::uniform_int_distribution<> d(0, 10);
std::function<int()> rnd = std::bind(d, e);
for(int n=0; n<10; ++n)
std::cout << rnd() << ' ';
std::cout << '\n';
// bind to a member function
Foo foo;
auto f3 = std::bind(&Foo::print_sum, foo, 95, _1);
f3(5);
// bind to member data
auto f4 = std::bind(&Foo::data, _1);
std::cout << f4(foo) << '\n';
}
Saída:
2 1 42 10 7
12 12 12 4 5
1 5 0 2 0 8 2 2 10 8
100
10
Veja também
(C++11) |
espaços reservados para os argumentos não ligados em uma expressão de std::bind Original: placeholders for the unbound arguments in a std::bind expression The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (constante) |
(C++11) |
cria um objecto de função de um apontador para um membro Original: creates a function object out of a pointer to a member The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (modelo de função) |