std::initializer_list
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| Defined in header <initializer_list>
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| template< class T > class initializer_list; |
（C++11 起） | |
std::initializer_list<T>类型的对象是一个轻量级的代理对象，它提供了访问的实施在未指定的存储（可以是自动的，暂时的或静态的只读存储器，视情况而定，分配到一个数组中的对象类型T ）Original:
An object of type
std::initializer_list<T> is a lightweight proxy object, which provides access to an array of objects of type T, allocated by the implementation in unspecified storage (which could be automatic, temporary, or static read-only memory, depending on the situation)The text has been machine-translated via Google Translate.
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该数组初始化一个
std::initializer_list对象被构造时，使用一个“支撑初始化列表”列表初始化，包括函数调用列表的初始化和赋值表达式（不要混淆构造函数初始化列表），或当“支撑初始化列表”，势必auto，包括中一个环..不等Original:
This array is initialized and a
std::initializer_list object is constructed when a braced-init-list is used in 列表初始化, including function-call list initialization and assignment expression (not to be confused with 构造函数初始化列表), or when braced-init-list is bound to auto, including in a ranged for loop.The text has been machine-translated via Google Translate.
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初始值设定项列表可能会被实现为一个对指针或指针和长度。复制
std::initializer_list不会复制的基础对象。不保证底层数组后原来的初始化列表中对象的生命周期已经结束Original:
Initializer list may be implemented as a pair of pointers or pointer and length. Copying a
std::initializer_list does not copy the underlying objects. The underlying array is not guaranteed to exist after the lifetime of the original initializer list object has ended.The text has been machine-translated via Google Translate.
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[编辑] 会员类型
| 会员类型
Original: Member 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
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T |
reference
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const T& |
const_reference
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const T& |
size_type
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size_t |
iterator
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const T* |
const_iterator
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const T* |
[编辑] 成员函数
| 创建一个空的初始值设定项列表 Original: creates an empty initializer list 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） | |
Original: Capacity The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. | |
| 返回在初始化列表中的元素个数 Original: returns the number of elements in the initializer list 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） | |
Original: Iterators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. | |
| 返回的第一个元素的指针 Original: returns a pointer the first element 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） | |
| 返回一个指针，指向一个过去的最后一个元素 Original: returns a pointer to one past the last element 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） | |
[编辑] 非成员函数
| 专业std::begin Original: specializes std::begin The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. （函数模板） | |
| 专业std::end Original: specializes std::end The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. （函数模板） | |
[编辑] 为例
#include <iostream> #include <vector> #include <initializer_list> template<class T> struct S { std::vector<T> v; S(std::initializer_list<T> l) : v(l) { std::cout << "constructed with a " << l.size() << "-element list\n"; } void append(std::initializer_list<T> l) { v.insert(v.end(), l.begin(), l.end()); } std::pair<const int*, size_t> c_arr() const { return {&v[0], v.size()}; // list-initialization in return statement } }; template<typename T> void templated_fn(T) { } int main() { S<int> s = {1,2,3,4,5}; // direct list-initialization s.append({6,7,8}); // list-initialization in function call std::cout << "The vector size is now " << s.c_arr().second << " ints:\n"; for(auto n : s.v) std::cout << ' ' << n; std::cout << '\n'; std::cout << "range-for over brace-init-list: \n"; for(int x : {-1, -2, -3}) // the rule for auto makes this ranged for work std::cout << x << ' '; std::cout << '\n'; auto al = {10, 11, 12}; // special rule for auto std::cout << "The list bound to auto has size() = " << al.size() << '\n'; // templated_fn({1,2,3}); // compiler error! "{1,2,3}" is not an expression, // it has no type, and so T cannot be deduced templated_fn<std::initializer_list<int>>({1,2,3}); // OK templated_fn<std::vector<int>>({1,2,3}); // also OK }
Output:
The vector size is now 8 ints: 1 2 3 4 5 6 7 8 range-for over brace-init-list: -1 -2 -3 The list bound to auto has size() = 3
