std::mem_fn

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C++
 
实用工具库
类型的支持 (basic types, RTTI, type traits)
动态内存管理
错误处理
程序实用工具
可变参数函数
日期和时间
函数对象
initializer_list（C++11）
bitset
hash（C++11）
关系运算符
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
双和元组
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Pairs and tuples
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pair
tuple（C++11）
piecewise_construct_t（C++11）
piecewise_construct（C++11）
掉期，远期和移动
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Swap, forward and move
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swap
forward（C++11）
move（C++11）
move_if_noexcept（C++11）
declval（C++11）
 
函数对象
功能包装
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Function wrappers
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function（C++11）
mem_fn（C++11）
bad_function_call（C++11）
绑定
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Bind
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bind（C++11）
is_bind_expression（C++11）
is_placeholder（C++11）
_1, _2, _3, ...（C++11）
参考包装
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Reference wrappers
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reference_wrapper（C++11）
ref
cref		（C++11）
（C++11）
操作包装
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Operator wrappers
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否定词
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Negators
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已过时粘合剂和适配器
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Deprecated binders and adaptors
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unary_function（过时了）
binary_function（过时了）
ptr_fun（过时了）
pointer_to_unary_function（过时了）
pointer_to_binary_function（过时了）
mem_fun（过时了）
mem_fun_t
mem_fun1_t
const_mem_fun_t
const_mem_fun1_t		（过时了）
（过时了）
（过时了）
（过时了）
mem_fun_ref（过时了）
mem_fun_ref_t
mem_fun1_ref_t
const_mem_fun_ref_t
const_mem_fun1_ref_t		（过时了）
（过时了）
（过时了）
（过时了）
binder1st
binder2nd		（过时了）
（过时了）
bind1st
bind2nd		（过时了）
（过时了）
 
Defined in header <functional>
template< class R, class T >
/*unspecified*/ mem_fn(R T::* pm);
 (1) （C++11 起）
template< class R, class T, class... Args >

/*unspecified*/ mem_fn(R (T::* pm)(Args...));
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) volatile);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const volatile);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) &);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const &);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) volatile &);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const volatile &);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) &&);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const &&);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) volatile &&);
template< class R, class T, class... Args >

/*unspecified*/ mem_fn(R (T::* pm)(Args...) const volatile &&);
 (2) （C + +11，但缺陷）
函数模板std::mem_fn生成包装对象指向成员的指针，它可以存储，复制和引用指向成员的指针。两个引用和指针（包括智能指针）的对象时，可以使用调用std::mem_fn.
Original:
Function template std::mem_fn generates wrapper objects for pointers to members, which can store, copy, and invoke a pointer to member. Both references and pointers (including smart pointers) to an object can be used when invoking a std::mem_fn.
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缺陷的重载（2）.
Original:
The overloads (2) are reported as defect.
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resolution，最近被评为“暂时就绪”建议取消所有的重载（2）.
Original:
The resolution, which has recently been voted "Tentatively Ready" proposes to remove all the overloads (2).
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这将打破一些代码，请参见示例3.
Original:
This will break some code, see Example 3.
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目录

[编辑] 参数

pm -
指针成员将包裹
Original:
pointer to member that will be wrapped
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[编辑] 返回值

std::mem_fn返回一个呼叫的类型不明确，它具有以下成员的包装
Original:
std::mem_fn returns an call wrapper of unspecified type that has the following members:
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的std :: mem_fn的
Original:
std::mem_fn
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 Return type

Member types

类型
Original:
type
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 definition
result_type
pm如果pm的返回类型是一个指向成员函数的指针，而不是定义为指针成员对象
Original:
the return type of pm if pm is a pointer to member function, not defined for pointer to member object
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argument_type
T*，可能是合格的简历，如果pm是一个指向成员函数没有参数
Original:
T*, possibly cv-qualified, if pm is a pointer to member function taking no arguments
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first_argument_type
T*如果pm是一个参数的成员函数的指针
Original:
T* if pm is a pointer to member function taking one argument
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second_argument_type
T1如果pm是一个指向成员函数的指针类型T1的一个参数
Original:
T1 if pm is a pointer to member function taking one argument of type T1
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Member function

operator()
调用指定对象上的目标，可选的参数
Original:
invokes the target on a specified object, with optional parameters
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（公共成员函数）

[编辑] 例外

无
Original:
None.
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[编辑] 实施例1

使用mem_fn储存和执行一个成员函数和一个成员对象：
Original:
Use mem_fn to store and execute a member function and a member object:
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#include <functional>
#include <iostream>
 
struct Foo {
  void display_greeting() {
    std::cout << "Hello, world.\n";
  }
  void display_number(int i) {
    std::cout << "number: " << i << '\n';
  }
  int data = 7;
};
 
int main() {
  Foo f;
 
  auto greet = std::mem_fn(&Foo::display_greeting);
  greet(f);
 
  auto print_num = std::mem_fn(&Foo::display_number);
  print_num(f, 42);
 
  auto access_data = std::mem_fn(&Foo::data);
  std::cout << "data: " << access_data(f) << '\n';
}

Output: 

Hello, world.
number: 42
data: 7

[编辑] 实施例2

通过一个成员函数std::transform创建一个数字序列
Original:
Pass a member function to std::transform to create a sequence of numbers:
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#include <iostream>
#include <functional>
#include <iterator>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
 
int main()
{
    std::vector<std::string> words = {"This", "is", "a", "test"};
    std::vector<std::unique_ptr<std::string>> words2;
    words2.emplace_back(new std::string("another"));
    words2.emplace_back(new std::string("test"));
 
    std::vector<std::size_t> lengths;
    std::transform(words.begin(),
                   words.end(),
                   std::back_inserter(lengths),
                   std::mem_fn(&std::string::size)); // uses references to strings
    std::transform(words2.begin(),
                   words2.end(),
                   std::back_inserter(lengths),
                   std::mem_fn(&std::string::size)); // uses unique_ptr to strings
 
    std::cout << "The string lengths are ";
    for(auto n : lengths) std::cout << n << ' ';
    std::cout << '\n';
}

Output: 

The string lengths are 4 2 1 4 7 4

[编辑] 实施例3

#include <functional>
 
struct X {
  int x;
 
        int& easy()      {return x;}
        int& get()       {return x;}
  const int& get() const {return x;}
};
 
 
int main(void)
{
    auto a = std::mem_fn        (&X::easy); // no problem at all
//  auto b = std::mem_fn<int&  >(&X::get ); // no longer works with new specification
    auto c = std::mem_fn<int&()>(&X::get ); // works with both old and new specification
    auto d = [] (X& x) {return x.get();};   // another approach to overload resolution
}


[编辑] 另请参阅

（C++11）
包装任何类型的可调用对象与指定的函数调用签名
Original:
wraps callable object of any type with specified function call signature
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（类模板） [edit]
（C++11）
绑定一个或多个参数的函数对象
Original:
binds one or more arguments to a function object
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（函数模板） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/utility/functional/mem_fn&oldid=26616”