std::is_default_constructible, std::is_trivially_default_constructible, std::is_nothrow_default_constructible

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_default_constructible;
 (1) （C++11 起）
template< class T >
struct is_trivially_default_constructible;
 (2) （C++11 起）
template< class T >
struct is_nothrow_default_constructible;
 (3) （C++11 起）
1)
检查一个类型是否是DefaultConstructible，即有一个可访问的显式或隐式的默认构造函数。如果符合要求，一个成员value等于true，否则value是false.
Original:
Checks whether a type is DefaultConstructible, i.e. has an accessible explicit or implicit default constructor. If the requirement is met, a member constant value equal true is provided, otherwise 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.
2)
同为1），但构造表达不调用任何操作，是不平凡的.
Original:
Same as 1), but the constructor expression does not call any operation that is not trivial.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
3)
1相同），但构造表达式noexcept.
Original:
Same as 1), but the constructor expression is noexcept.
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 default-constructible ，false其他方式
Original:
true if T is default-constructible , 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_default_constructible : std::is_constructible<T> {};
 
template< class T>
struct is_trivially_default_constructible : std::is_trivially_constructible<T> {};
 
template< class T>
struct is_nothrow_default_constructible : std::is_nothrow_constructible<T> {};

[编辑] 为例

#include <iostream>
#include <type_traits>
 
struct Ex1 {
    std::string str; // member has a non-trivial default ctor
};
struct Ex2 {
    int n;
    Ex2() = default; // trivial and non-throwing
};
 
int main() {
    std::cout << std::boolalpha << "Ex1 is default-constructible? "
              << std::is_default_constructible<Ex1>::value << '\n'
              << "Ex1 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex1>::value << '\n'
              << "Ex2 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex2>::value << '\n';
              << "Ex2 is nothrow default-constructible? "
              << std::is_nothrow_default_constructible<Ex2>::value << '\n';
}

Output: 

Ex1 is default-constructible? true
Ex1 is trivially default-constructible? false
Ex2 is trivially default-constructible? true
Ex2 is nothrow default-constructible? true

[编辑] 另请参阅

（C++11）
（C++11）
（C++11）
检查如果一个类型有一个构造函数的具体参数
Original:
checks if a type has a constructor for specific arguments
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]
（C++11）
（C++11）
（C++11）
一类的检查，如果有拷贝构造函数
Original:
checks if a type has a copy constructor
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]
（C++11）
（C++11）
（C++11）
类型检查，如果有一个移动的构造函数
Original:
checks if a type has a move constructor
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_default_constructible&oldid=27496”