Summary of the usage of vector in C ++

Summary of the usage of vector in C ++

This article mainly introduces that vector is a very useful container in c ++. Let's make a summary of this container.

1. Basic operations

 

(1) header file # include <vector>.

 

(2) create a vector object, vector <int> vec;

 

(3) Insert numbers at the end: vec. push_back ();

 

(4) use a subscript to access the element. cout <vec [0] <endl; remember that the subscript starts from 0.

 

(5) use an iterator to access elements.

 

 

The Code is as follows:

Vector <int>: iterator it;

For (it = vec. begin (); it! = Vec. end (); it ++)

Cout <* it <endl;

 

 

(6) insert element: vec. insert (vec. begin () + I, a); insert a before the I + 1 element;

 

(7) delete element: vec. erase (vec. begin () + 2); Delete 3rd Elements

 

Vec. erase (vec. begin () + I, vec. end () + j); Delete interval [I, J-1]; interval starts from 0

 

(8) vector size: vec. size ();

 

(9) clear: vec. clear ();

 

2

 

The element of a vector can not only be int, double, string, but also struct. Note that the struct must be defined as global; otherwise, an error may occur. The following is a short program code:

 

 

The Code is as follows:

# Include <stdio. h>

# Include <algorithm>

# Include <vector>

# Include <iostream>

Using namespace std;

 

Typedef struct rect

{

Int id;

Int length;

Int width;

 

// For a vector element that is a struct, you can define a comparison function within the struct, Which is sorted in ascending order by id, length, and width.

Bool operator <(const rect & a) const

{

If (id! = A. id)

Return id <a. id;

Else

{

If (length! = A. length)

Return length <a. length;

Else

Return width <a. width;

}

}

} Rect;

 

Int main ()

{

Vector <Rect> vec;

Rect rect;

Rect. id = 1;

Rect. length = 2;

Rect. width = 3;

Vec. push_back (rect );

Vector <Rect>: iterator it = vec. begin ();

Cout <(* it). id <''<(* it). length <'' <(* it). width <endl;

 

Return 0;

 

}

 

 

3 Algorithm

 

(1) Use reverse to flip the element: header file # include <algorithm>

 

Reverse (vec. begin (), vec. end (); flip the element (in vector, if two iterators are required in a function,

 

Generally, the last one does not contain .)

 

(2) sort by sort: the header file is required # include <algorithm>,

 

Sort (vec. begin (), vec. end (); (Ascending by default, that is, ascending ).

 

You can rewrite the sort comparison function to compare data in descending order, as shown below:

 

Define the sorting comparison function:

 

 

Copy the Code as follows:

Bool Comp (const int & a, const int & B)

{

Return a> B;

}

 

When calling: sort (vec. begin (), vec. end (), Comp) to sort in descending order.