C + + Map common usage Instructions __c++

http://blog.csdn.net/shuzfan/article/details/53115922# three-take value

One declaration of two insert operations 1 use Insert for single and multiple inserts three values four capacity query five iterators Six remove Exchange 1 Remove 2 interchange Seven order comparison eight find nine operator

C + + map provides a key value to the container, where the data are in pairs, the following figure: the first value in each pair is called a keyword (key), each keyword can only appear once in the map, the second is called the corresponding value of the keyword.

—————————————————————————————————————————————— A. Statement

Header file
#include <map>

map<int, string> id_name;

Assignment with {} is started from c++11, so it will be an error when the compiler version is too low, such as Visual Studio
Map<int, string> id_name = {
                {2015, "Jim"},
                {2 016, "Tom"},
                {2017, "Bob"}};

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—————————————————————————————————————————————— two. Insert Operation 2.1 use [] for a single insert

Map<int, string> id_name;

If a key value of 2015 is already present, the assignment modification is done, and if not, insert
id_name[2015] = "Tom";

1 2 3 4 2.1 Single and multiple inserts using Insert

There are 4 overloaded functions for an insert:

Inserts a single key value pair and returns the insertion position and success flag, when the insertion position already exists, the insert fails
pair<iterator,bool> Insert (const value_type& val);

Inserts at the specified position, the insertion efficiency at different positions is not the same because it involves rearrangement of
iterator inserts (const_iterator position, const value_type& val);

Inserts multiple
void inserts (Inputiterator-I, Inputiterator last);

C++11 begins to support using a list to insert multiple   
void inserts (initializer_list<value_type> il);

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The following are examples of specific uses:

#include <iostream> #include <map> int main () {Std::map<char, int> mymap;
    Inserts a single value Mymap.insert (std::p air<char, int> (' A ', 100));

    Mymap.insert (std::p air<char, int> (' Z ', 200));
    Returns the insertion position and whether to insert a successful std::p Air<std::map<char, Int>::iterator, bool> ret;
    RET = Mymap.insert (std::p air<char, int> (' Z ', 500));
        if (Ret.second = = False) {std::cout << "element ' Z ' already existed";
    Std::cout << "with a value of" << ret.first->second << ' \ n ';
    }//Specify position to insert Std::map<char, int>::iterator it = Mymap.begin ();  Mymap.insert (IT, std::p air<char, int> (' B ', 300));  Higher efficiency Mymap.insert (IT, std::p air<char, int> (' C ', 400));
    Efficiency not highest//range multi-valued inserts Std::map<char, int> Anothermap;

    Anothermap.insert (Mymap.begin (), Mymap.find (' C '));

    The list form is inserted into the Anothermap.insert ({{' d ',}, {' E ', 200}}});
return 0; }

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—————————————————————————————————————————————— three. Take a value

The element values in the map are primarily at and [], and at will be checked for subscript, and [] not.

Map<int, string> id_name;

There is no keyword 2016 in id_name, using [] to take a value will cause the insertion
//Therefore, the following statement will not error, but the print result is empty
cout<<id_name[2016].c_str () <<endl;

Keyword checking is done using at, so the following statement complains
id_name.at (2016) = "Bob";

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—————————————————————————————————————————————— Four. Capacity Query

Query whether the map is an empty
bool empty ();

The number of key-value pairs in the query map
size_t size ();

The maximum number of key values that the query map can contain is related to the system and the application library.
//In addition, this does not mean that the user must be able to save so much, it is likely that the memory has failed to reach the
size_t max_size ();

The number of elements that the query keyword is key to, in the map result is not 0 namely 1
size_t count (const key& Key) const;

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—————————————————————————————————————————————— five. iterators

There are eight functions to get iterators: * Begin, end, rbegin,rend*, and corresponding * Cbegin, cend, crbegin,crend*.

The difference is that the latter must return const_iterator, while the former returns iterator or const_iterator based on the type of map. In the const case, the value is not allowed to be modified. As shown in the following code:

Map<int,int>::iterator it;
Map<int,int> mmap;
Const map<int,int> Const_mmap;

it = Mmap.begin (); Iterator
Mmap.cbegin ();//const_iterator

const_mmap.begin ();//const_iterator
Const_mmap.cbegin (); Const_iterator

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The returned iterator can perform a subtraction operation, in addition, if the map is empty, begin = end.

—————————————————————————————————————————————— six. Delete swap 6.1 Delete

//delete the key-value pair that the iterator points to, and return an iterator to the next element iterator erase (iterator POS)//delete a certain range of elements and return an iterator iterator erase to the next element (Const_ite

Rator, Const_iterator last);

According to the key to delete, return the number of deleted elements, in the map results are not 0 or 1 size_t erase (const key_type& key); Empty the map and empty the size to 0