map
map是一种关联容器,存储相结合形成的一个关键值和映射值的元素。Map 是一种Pair Associative Container,意味着它的值类型为 pair
map具有重要的属性,就是在map对象中插入一个新元素不指向现有元素的迭代器失效。从map上删除一个元素,也没有任何迭代器失效,除非,当然,实际上指向正在被删除的元素的迭代器。
1、例子
struct ltstr
{
bool operator()(const char* s1, const char* s2) const
{
return strcmp(s1, s2) < 0;
}
};
int main()
{
map months;
months["january"] = 31;
months["february"] = 28;
months["march"] = 31;
months["april"] = 30;
months["may"] = 31;
months["june"] = 30;
months["july"] = 31;
months["august"] = 31;
months["september"] = 30;
months["october"] = 31;
months["november"] = 30;
months["december"] = 31;
cout << "june -> " << months["june"] << endl;
map::iterator cur = months.find("june");
map::iterator prev = cur;
map::iterator next = cur;
++next;
--prev;
cout << "Previous (in alphabetical order) is " << (*prev).first << endl;
cout << "Next (in alphabetical order) is " << (*next).first << endl;
}
2、定义形式
template < class Key, class T, class Compare = less,
class Allocator = allocator > > class map;
3、模板参数具有以下涵义:
key:关键值的类型。在map对象中的每个元素是通过该关键值唯一确定元素的。
T:映射值的类型。在map中的每个元素是用来储存一些数据作为其映射值。
compare:Comparison类:A类键的类型,它有两个参数,并返回一个bool。表达comp(A,B),comp是这比较类A和B是关键值的对象,应返回true,如果是在早先的立场比B放置在一个严格弱排序操作。这可以是一个类实现一个函数调用运算符或一个函数的指针(见一个例子构造)。默认的对于
Map对象使用这个表达式来确定在容器中元素的位置。以下这个规则在任何时候都排列在map容器中的所有元素。
Allocator:用于定义存储分配模型分配器对象的类型。默认情况下,分配器类模板,它定义了最简单的内存分配模式,是值独立的
map::iterator it;
(*it).first; // 指向key值(of type Key)
(*it).second; // 映射的值(of type T)
(*it); // the "element value" (of type pair)
也可以如下表达:
it->first; // same as (*it).first (the key value)
it->second; // same as (*it).second (the mapped value)
4、成员变量和成员函数
Member | Where defined | Description |
---|---|---|
key_type | Associative Container | map中的key类型 |
data_type | Pair Associative Container | key关联的值类型 |
value_type | Pair Associative Container | 对象类型, pair |
key_compare | Sorted Associative Container | Function object 通过顺序比较 |
value_compare | Sorted Associative Container | Function object that compares two values for ordering. |
pointer | Container | Pointer to T. |
reference | Container | Reference to T |
const_reference | Container | Const reference to T |
size_type | Container | An unsigned integral type. |
difference_type | Container | A signed integral type. |
iterator | Container | Iterator used to iterate through a map. [1] |
const_iterator | Container | Const iterator used to iterate through a map. |
reverse_iterator | Reversible Container | Iterator used to iterate backwards through a map. [1] |
const_reverse_iterator | Reversible Container | Const iterator used to iterate backwards through a map. |
iterator begin() | Container | Returns an iterator pointing to the beginning of the map. |
iterator end() | Container | Returns an iterator pointing to the end of the map. |
const_iterator begin() const | Container | Returns a const_iterator pointing to the beginning of themap. |
const_iterator end() const | Container | Returns a const_iterator pointing to the end of the map. |
reverse_iterator rbegin() | Reversible Container | Returns a reverse_iterator pointing to the beginning of the reversed map. |
reverse_iterator rend() | Reversible Container | Returns a reverse_iterator pointing to the end of the reversed map. |
const_reverse_iterator rbegin() const | Reversible Container | Returns a const_reverse_iterator pointing to the beginning of the reversed map. |
const_reverse_iterator rend() const | Reversible Container | Returns a const_reverse_iterator pointing to the end of the reversed map. |
size_type size() const | Container | Returns the size of the map. |
size_type max_size() const | Container | Returns the largest possible size of the map. |
bool empty() const | Container | true if the map's size is 0. |
key_compare key_comp() const | Sorted Associative Container | Returns the key_compare object used by the map. |
value_compare value_comp() const | Sorted Associative Container | Returns the value_compare object used by the map. |
map() | Container | Creates an empty map. |
map(const key_compare& comp) | Sorted Associative Container | Creates an empty map, using comp as the key_compare object. |
template |
Unique Sorted Associative Container | Creates a map with a copy of a range. |
template |
Unique Sorted Associative Container | Creates a map with a copy of a range, using comp as thekey_compare object. |
map(const map&) | Container | The copy constructor. |
map& operator=(const map&) | Container | The assignment operator |
void swap(map&) | Container | Swaps the contents of two maps. |
pair |
Unique Associative Container | Inserts x into the map. |
iterator insert(iterator pos, const value_type& x) |
Unique Sorted Associative Container | Inserts x into the map, using pos as a hint to where it will be inserted. |
template |
Unique Sorted Associative Container | Inserts a range into the map. |
void erase(iterator pos) | Associative Container | Erases the element pointed to by pos. |
size_type erase(const key_type& k) | Associative Container | Erases the element whose key is k. |
void erase(iterator first, iterator last) | Associative Container | Erases all elements in a range. |
void clear() | Associative Container | Erases all of the elements. |
iterator find(const key_type& k) | Associative Container | Finds an element whose key is k. |
const_iterator find(const key_type& k) const | Associative Container | Finds an element whose key is k. |
size_type count(const key_type& k) | Unique Associative Container | Counts the number of elements whose key is k. |
iterator lower_bound(const key_type& k) | Sorted Associative Container | Finds the first element whose key is not less than k. |
const_iterator lower_bound(const key_type& k) const | Sorted Associative Container | Finds the first element whose key is not less than k. |
iterator upper_bound(const key_type& k) | Sorted Associative Container | Finds the first element whose key greater than k. |
const_iterator upper_bound(const key_type& k) const | Sorted Associative Container | Finds the first element whose key greater than k. |
pair |
Sorted Associative Container | Finds a range containing all elements whose key is k. |
pair |
Sorted Associative Container | Finds a range containing all elements whose key is k. |
data_type& operator[](const key_type& k) [3] |
map | See below. |
bool operator==(const map&, const map&) |
Forward Container | Tests two maps for equality. This is a global function, not a member function. |
bool operator<(const map&, const map&) |
Forward Container | Lexicographical comparison. This is a global function, not a member function. |
下面展示了常用的一些方法。
// stu_map.cpp : 定义控制台应用程序的入口点。 // #include "stdafx.h" #include
运行结果: