std::remove_cv, std::remove_const, std::remove_volatile

 

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bitset
hash (C++11)
integer_sequence (C++14)
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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
比较 (C++20)
three_way_comparablethree_way_comparable_with
strong_ordering weak_ordering partial_ordering common_comparison_category compare_three_way_result compare_three_way	strong_order weak_order partial_order compare_strong_order_fallback compare_weak_order_fallback compare_partial_order_fallback	is_eqis_neqis_ltis_lteqis_gtis_gteq
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pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
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基本类型
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ptrdiff_t size_t max_align_t (C++11) byte (C++17)	nullptr_t (C++11) offsetof NULL
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C 数值极限接口
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type_info type_index (C++11)	bad_typeid bad_cast
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is_rvalue_reference (C++11)
is_member_pointer (C++11)
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is_member_function_pointer (C++11)

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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)
常量求值语境
is_constant_evaluated (C++20)

受支持操作
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)
关系与属性查询
is_same (C++11) is_base_of (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)	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)
类型变换
aligned_storage (C++11) aligned_union (C++11) 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)(C++20 前)(C++17) type_identity (C++20)

 

定义于头文件 <type_traits>
template< class T > struct remove_cv;	(1)	(C++11 起)
template< class T > struct remove_const;	(2)	(C++11 起)
template< class T > struct remove_volatile;	(3)	(C++11 起)

提供与 T 相同的成员 typedef type ，除了其最顶层 cv 限定符被移除。

1) 移除最顶层 const 、最顶层 volatile 或两者，若存在。

2) 移除最顶层 const

3) 移除最顶层 volatile

成员类型

名称	定义
type	无 cv 限定符的 T

辅助类型

template< class T > using remove_cv_t       = typename remove_cv<T>::type;		(C++14 起)
template< class T > using remove_const_t    = typename remove_const<T>::type;		(C++14 起)
template< class T > using remove_volatile_t = typename remove_volatile<T>::type;		(C++14 起)

可能的实现

template< class T > struct remove_cv { typedef typename std::remove_volatile<typename std::remove_const<T>::type>::type type; };   template< class T > struct remove_const { typedef T type; }; template< class T > struct remove_const<const T> { typedef T type; };   template< class T > struct remove_volatile { typedef T type; }; template< class T > struct remove_volatile<volatile T> { typedef T type; };

示例

从 const volatile int * 移除 const/volatile 不修改该类型，因为该指针自身既非 const 亦非 volatile 。

运行此代码

#include <iostream>
#include <type_traits>
 
int main() {
    typedef std::remove_cv<const int>::type type1;
    typedef std::remove_cv<volatile int>::type type2;
    typedef std::remove_cv<const volatile int>::type type3;
    typedef std::remove_cv<const volatile int*>::type type4;
    typedef std::remove_cv<int * const volatile>::type type5;
 
    std::cout << "test1 " << (std::is_same<int, type1>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test2 " << (std::is_same<int, type2>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test3 " << (std::is_same<int, type3>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test4 " << (std::is_same<const volatile int*, type4>::value
        ? "passed" : "failed") << '\n';
    std::cout << "test5 " << (std::is_same<int*, type5>::value
        ? "passed" : "failed") << '\n';
}

输出：

test1 passed
test2 passed
test3 passed
test4 passed
test5 passed

参阅

is_const (C++11)	检查类型是否为 const 限定 (类模板)
is_volatile (C++11)	检查类型是否为 volatile 限定 (类模板)
add_cvadd_constadd_volatile (C++11)(C++11)(C++11)	添加 const 或/与 volatile 限定符到给定类型 (类模板)
remove_cvref (C++20)	将 std::remove_cv 与 std::remove_reference 结合 (类模板)