std::is_const

来自cppreference.com

This page has been machine-translated from the English version of the wiki using Google Translate.

The translation may contain errors and awkward wording. Hover over text to see the original version. You can help to fix errors and improve the translation. For instructions click here.

Click here for the English version of this page

 
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
Original:
Relational operators
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
双和元组
Original:
Pairs and tuples
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
pair
tuple（C++11）
piecewise_construct_t（C++11）
piecewise_construct（C++11）
掉期，远期和移动
Original:
Swap, forward and move
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
swap
forward（C++11）
move（C++11）
move_if_noexcept（C++11）
declval（C++11）
 
类型的支持
基本类型
Original:
Basic types
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
基本类型
固定宽度的整数类型 （C++11）
nullptr_t（C++11）
offsetof
NULL
数值范围内
Original:
Numeric limits
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
numeric_limits
C数字限制接口
运行时类型信息
Original:
Runtime type information
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
type_info
type_index（C++11）
类型特征
Original:
Type traits
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
初级型两类
Original:
Primary type categories
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
is_void（C++11）
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
Original:
Type properties
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
is_const（C++11）
is_volatile（C++11）
is_pod（C++11）
is_empty（C++11）
is_polymorphic（C++11）
is_abstract（C++11）
is_trivial（C++11）
is_trivially_copyable（C++11）
is_standard_layout（C++11）
is_literal_type（C++11）
is_signed（C++11）
is_unsigned（C++11）
支持的操作
Original:
Supported operations
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
is_constructible
is_trivially_constructible
is_nothrow_constructible		（C++11）
（C++11）
（C++11）
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible		（C++11）
（C++11）
（C++11）
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible		（C++11）
（C++11）
（C++11）
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible		（C++11）
（C++11）
（C++11）
is_assignable
is_trivially_assignable
is_nothrow_assignable		（C++11）
（C++11）
（C++11）
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable		（C++11）
（C++11）
（C++11）
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable		（C++11）
（C++11）
（C++11）
is_destructible
is_trivially_destructible
is_nothrow_destructible		（C++11）
（C++11）
（C++11）
has_virtual_destructor（C++11）
关系和属性查询
Original:
Relationships and property queries
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
is_same（C++11）
is_base_of（C++11）
is_convertible（C++11）
alignment_of（C++11）
rank（C++11）
extent（C++11）
类型的修改
Original:
Type modifications
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
remove_cv
remove_const
remove_volatile		（C++11）
（C++11）
（C++11）
add_cv
add_const
add_volatile		（C++11）
（C++11）
（C++11）
make_signed（C++11）
make_unsigned（C++11）
remove_reference（C++11）
add_lvalue_reference
add_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
Original:
Type transformations
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
aligned_storage（C++11）
aligned_union（C++11）
decay（C++11）
enable_if（C++11）
conditional（C++11）
common_type（C++11）
underlying_type（C++11）
result_of（C++11）
键入特征常数
Original:
Type trait constants
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
integral_constant（C++11）
 
Defined in header <type_traits>
template< class T >
struct is_const;
 （C++11 起）
T是一个const限定的类型（即，const，或const volatile），提供会员value等于true。对于任何其他类型，value是false.
Original:
If T is a const-qualified type (that is, const, or const volatile), provides the member constant value equal true. For any other type, value is false.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

目录

Inherited from std::integral_constant

Member constants

value
[静态的] </ SPAN></div></div>
true如果 T is a const-qualified type ，false其他方式
Original:
true if T is a const-qualified type , false otherwise
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

（公共静态成员常量）

Member functions

operator bool
转换的对象bool，返回value
Original:
converts the object to bool, returns value
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

（公共成员函数）

Member types

类型
Original:
Type
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
 Definition
value_type bool
type std::integral_constant<bool, value>

</div>

[编辑] 可能的实现

template<class T> struct is_const          : std::false_type {};
template<class T> struct is_const<const T> : std::true_type {};

[编辑] 为例

#include <iostream>
#include <type_traits>
 
int main()
{
    std::cout << boolalpha;
    std::cout << std::is_const<int>::value << '\n';
    std::cout << std::is_const<const int>::value  << '\n';
}

Output: 

false
true

[编辑] 另请参阅

（C++11）
类型检查，如果是挥发合格的
Original:
checks if a type is volatile-qualified
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

（类模板） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/types/is_const&oldid=27542”