A common use of pair

It is a very useful pair of "gadgets", when it is desired to tie together two elements as a composite element, and therefore do not want the definition of the structure, can easily use the pair as a substitute. That is, a pair can be considered as two elements of internal structure, and these two types of elements can be specified as the following short code:

struct pair{
    typeName1 first;
    typeName2 second;
}

Defined pair of

head File

#include<utility>	 
using namespace std;

Since when have used the map to realize pair, so remember utility, you can use the map header files

definition

pair<typeName1, typeName2> name;

pair<string, int> p;

If you want to initialize when defining pair, just to keep up with a small parenthesis

pair<string, int> p("gqq", 5);

If you want to build in the code 临时的pair , there are two ways:

The embodiment of the two element type definition EDITORIAL parentheses, followed by

pair<string, int>("gqq", 5);

Use its ownmake_pair函数

make_pair("gqq", 5);

Access pair of elements

Only two elements in pair, respectively, first and second, only need a normal installation structure to access

#include<iostream>
#include<utility>
#include<string>
using namespace std;

int main(){
    pair<string, int> p;
    p.first = "zgq";
    p.second = 5;
    cout << p.first << " " << p.second << endl;
    p = make_pair("yzy", 55);
    cout << p.first << " " << p.second << endl;
    p = pair<string, int>("wjy", 555);
    cout << p.first << " " << p.second << endl;
    return 0;
}

zgq 5
yzy 55
wjy 555

pair commonly used functions

Comparison of operands

Two types of data pair can directly ==、!=、<、<=、>、>=compare the size comparison rule is first in first size as a standard, only when the first size is equal to judge if the second

#include<iostream>
#include<utility>
#include<string>
using namespace std;

int main(){
    pair<int, int> p1(5, 10);
    pair<int, int> p2(5, 15);
    pair<int, int> p3(10, 5);
    if(p1 < p3) printf("p1 < p3\n");
    if(p1 <= p3) printf("p1 <= p3\n");
    if(p1 < p2) printf("p1 < p2\n");
    return 0;
}

p1 < p3
p1 <= p3
p1 < p2

Common uses pair of

Used in place of the dual structure member and constructors, it can save time coding
As for the keys of the map to be inserted

#include<iostream>
#include<map>
#include<string>
using namespace std;

int main(){
    map<string, int> mp;
    mp.insert(make_pair("gqq", 5));
    mp.insert(pair<string, int>("yzy", 10));
    for(map<string, int>::iterator it = mp.begin(); it != mp.end(); it++){
        cout << it -> first << " " << it -> second << endl;

    }
    return 0;
}

gqq 5
yzy 10

Write by Gqq

Algorithms notes - Standard Template Library STL - pair