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C++11提供的新类型，定义在<initializer_list>头文件中。
template< class T > class initializer_list;
先说它的用处吧，然后再详细介绍一下。
首先有了initializer_list之后，对于STL的container的初始化就方便多了,比如以前初始化一个vector需要这样：
int a[] = {0, 1, 2, 3}; std::vector<int> vec(a, a+sizeof(a));
或者
std::vector<int> vec; vec.push_back(1); vec.push_back(3); vec.push_back(3); vec.push_back(2);
有了initializer_list后，就可以直接像初始化数组一样：
class Test { private: static std::map<string, string> const nameToBirthday = { {"lisi", "18841011"}, {"zhangsan", "18850123"}, {"wangwu", "18870908"}, {"zhaoliu", "18810316"}, }; }
当然啦，里面的std::map必须提供参数为initializer_list的构造函数如：
map( std::initializer_list<value_type> init, const Compare& comp = Compare(), const Allocator& alloc = Allocator() );
其实for（initializer： list）中如果list是个形如：{a, b, c...}，那么其实list自动被构造成了initializer_list对象。
下面稍微介绍一下initializer_list
一个initializer_list当出现在以下两种情况的被自动构造：
也就是说initializer_list对象只能用大括号{}初始化。
拷贝一个initializer_list对象并不会拷贝里面的元素。其实只是引用而已。而且里面的元素全部都是const的。
下面一个例子可以帮助我们更好的理解如何使用initializer_list:
#include <iostream> #include <vector> #include <initializer_list> using namespace std; template <class T> struct S { vector<T> v; S(initializer_list<T> l) : v(l){ cout << "constructed with a " << l.size() << "-elements lists" << endl; } void append(std::initializer_list<T> l) { v.insert(v.end(), l.begin(), l.end()); } pair<const T*, size_t> c_arr() const{ return {&v[0], v.size()}; } }; template <typename T> void templated_fn(T arg) { for (auto a : arg) cout << a << " "; cout << endl; } int main() { S<int> s = {1, 2, 3, 4, 5}; //automatically construct a initializer_list // object and copy it s.append({6, 7 , 8}); //list-initialization in function call cout << "The vector size is now " << s.c_arr().second << " ints:" << endl; for (auto n : s.v) cout << ‘ ‘ << n; cout << endl; cout << "range-for over brace-init-list: " << endl; for (auto x : {-1, -2, 03}) //// the rule for auto makes this ranged for work cout << x << " "; cout << endl; auto al = {10, 11, 12}; //special rule for auto cout << "The list bound to auto has size() = " << al.size() << endl; //templated_fn({1, 2, 3}); //compiler error! "{1, 2, 3}" is not an expressionit has no type, and so T cannot be duduced. templated_fn<initializer_list<int> > ({7, 8, 9}); //ok templated_fn<vector<int> >({3, 5, 7}); //also ok return 0; }
Reference：
http://en.cppreference.com/w/cpp/utility/initializer_list
http://www.cppblog.com/liyiwen/archive/2009/07/26/91248.html
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原文地址：http://www.cnblogs.com/lysuns/p/4278589.html
