STL map detailed usage

Map is associated with a container of the STL, which provides one (which can be referred to as a first key, each keyword can appear only once in the map, the second value is called the key) a data processing ability.

Required libraries

#include <map>

Basic Operations

definition

map<string,int>m;

This is the definition of a string with a keyword to the value of the map int

insert

method 1:

map<string,int>m;
m["Bob"]=101;    
m["Alice"]=102;  
m["Eric"]=103;

Method 2:

m.insert(pair<string,int>("Lee",104));

Method 3:

m.insert(map<string,int>::value_type("Karen",105));

Traversal

Defines a pointer iteration iter, to point map, the map of traversal.

#include<bits/stdc++.h>

using namespace std;

int main()
{
    map<string,int>m;
    m["Bob"]=101;
    m["Alice"]=102;
    m["Eric"]=103;
    map<string,int>::iterator iter;
    for(iter=m.begin(); iter!=m.end(); iter++)
        cout<<iter->first <<"->"<<iter->second<<endl;
}

The output is:

Alice->102
Bob->101
Eric->103

See map keywords automatically prevail in the interior, by lexicographic ordering, rather than sequentially input;

Note that when I experiment, I found such a phenomenon:

#include<bits/stdc++.h>

using namespace std;

int main()
{
    map<string,int>m;
    m["Bob"]=101;
    m["Alice"]=102;
    m["Eric"]=103;
    map<string,int>::iterator iter;
    for(iter=m.begin(); iter!=m.end(); iter++)
        cout<<iter->first <<"->"<<iter->second<<endl;
        
    if(m["AAA"]==0)
    cout<<"NO"<<endl;

    for(iter=m.begin(); iter!=m.end(); iter++)
        cout<<iter->first <<"->"<<iter->second<<endl;
        

}

When asked about the number of a map that does not exist when the returned value should be zero, but when you once again traverse, you will find the map has been more than a key-value pair, but the value is 0:

Alice->102
Bob->101
Eric->103
NO
AAA->0
Alice->102
Bob->101
Eric->103

Be sure to take good care of when do problems.

Seek

method 1:

cout<<m.find("Bob")->second<<endl;

If you search by keyword, search words will not garbled output

Method 2:

    map<string,int>::iterator iter1;
    iter1 = m.find(string("Bob"));
    if(iter1 != m.end())
    cout<<iter1->first <<"->"<<iter1->second<<endl;
    else    
    cout<<"no fount"<<endl;

Define a pointer to map, if not, returns m.end ()

delete

method 1

m.erase(iter1);

The same operation is pointer

Method 2

m.erase(string("AAA"));

Or delete keyword

map of the correlation function

begin () returns a pointer to the head of the map iterator
clear () removes all elements
count () returns the number of occurrence of the specified element
empty () if the map is empty Returns true
end () returns a pointer to the end of the map iterator
equal_range () return a special entry iterators
erase () removes an element
find () to find an element
get_allocator () Returns the map configurator
insert () insert elements
key_comp () function returns the key elements of the comparison
lower_bound () Returns the key-value> = a given element in a first position
MAX_SIZE () Returns the maximum number of elements that can be accommodated
rbegin () returns a pointer to the tail of the reverse map iterator
rend () returns a pointer to the head of the reverse map iterator
size () Returns the number of elements in the map
swap () exchanging two map
upper_bound, () Returns the key value> given element in a first position
value_comp () function returns the value of the comparison element