std::add_pointer

 

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类型类别 is_void (C++11) is_null_pointer (C++14)   is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_reference (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) 类型属性 is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(直到 C++20*) is_pod (C++11)(C++20 中已弃用) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) 类型特征常量 integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) 元函数 conjunction (C++17) disjunction (C++17) negation (C++17)	支持的操作 is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) 关系和属性查询 is_same (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) is_base_of (C++11) is_virtual_base_of (C++26) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) 类型修改 remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) 类型转换 aligned_storage (C++11)(C++23 中已弃用) aligned_union (C++11)(C++23 中已弃用) decay (C++11) remove_cvref (C++20) enable_if (C++11) void_t (C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) result_ofinvoke_result (C++11)(直到 C++20*)(C++17) type_identity (C++20)
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编译时整数序列
integer_sequence (C++14)

 

定义在头文件中 <type_traits>
template< class T > struct add_pointer;		(自 C++11 起)

如果 T 是一个 可引用类型 或（可能限定了 cv 的）void，则提供的成员 typedef type 为 typename std::remove_reference<T>::type*.

否则，提供的成员 typedef type 为 T。

如果程序为 std::add_pointer 添加了专门化，则行为未定义。

嵌套类型

名称	定义
type	如上所述确定

辅助类型

template< class T > using add_pointer_t = typename add_pointer<T>::type;		(自 C++14 起)

可能的实现

namespace detail { template<class T> struct type_identity { using type = T; }; // or use std::type_identity (since C++20)   template<class T> auto try_add_pointer(int) -> type_identity<typename std::remove_reference<T>::type*>; // usual case   template<class T> auto try_add_pointer(...) -> type_identity<T>; // unusual case (cannot form std::remove_reference<T>::type*) } // namespace detail   template<class T> struct add_pointer : decltype(detail::try_add_pointer<T>(0)) {};

示例

运行此代码

#include <iostream>
#include <type_traits>
 
template<typename F, typename Class>
void ptr_to_member_func_cvref_test(F Class::*)
{
    // F is an “abominable function type”
    using FF = std::add_pointer_t<F>;
    static_assert(std::is_same_v<F, FF>, "FF should be precisely F");
}
 
struct S
{
    void f_ref() & {}
    void f_const() const {}
};
 
int main()
{
    int i = 123;
    int& ri = i;
    typedef std::add_pointer<decltype(i)>::type IntPtr;
    typedef std::add_pointer<decltype(ri)>::type IntPtr2;
    IntPtr pi = &i;
    std::cout << "i = " << i << '\n';
    std::cout << "*pi = " << *pi << '\n';
 
    static_assert(std::is_pointer_v<IntPtr>, "IntPtr should be a pointer");
    static_assert(std::is_same_v<IntPtr, int*>, "IntPtr should be a pointer to int");
    static_assert(std::is_same_v<IntPtr2, IntPtr>, "IntPtr2 should be equal to IntPtr");
 
    typedef std::remove_pointer<IntPtr>::type IntAgain;
    IntAgain j = i;
    std::cout << "j = " << j << '\n';
 
    static_assert(!std::is_pointer_v<IntAgain>, "IntAgain should not be a pointer");
    static_assert(std::is_same_v<IntAgain, int>, "IntAgain should be equal to int");
 
    ptr_to_member_func_cvref_test(&S::f_ref);
    ptr_to_member_func_cvref_test(&S::f_const);
}

输出

i = 123
*pi = 123
j = 123

缺陷报告

以下行为更改的缺陷报告被追溯应用于先前发布的 C++ 标准。

DR	应用于	发布的行为	正确行为
LWG 2101	C++11	如果 T 是一个具有 cv 或 ref 的 函数类型，则程序格式错误。	在这种情况下产生的类型为 T。

另请参阅

is_pointer (C++11)	检查类型是否为指针类型 (类模板)
remove_pointer (C++11)	从给定类型中移除指针 (类模板)