Detailed explanation of c++ vector usage

Detailed explanation of vector usage

vector is an important member of C STL. When using it, you need to include the header file ：

#include<vector>;

1. Initialization of vector: There are five ways. Examples are as follows:

Recommended: "C Tutorial"

(1 ) vector a(10); //A vector of 10 integer elements is defined (the element type name is in angle brackets, which can be any legal data type), but no initial value is given, and its value is not sure.

(2) vector a(10,1); //A vector of 10 integer elements is defined, and the initial value of each element is given as 1

( 3) vector a(b); //Use b vector to create a vector, overall copy assignment

(4)vector a(b.begin(),b.begin 3 ); //The value of a is defined as the 0th to 2nd (total 3) elements in b

(5) int b[7]={1,2,3,4,5, 9,8};

        vector a(b,b 7); //Get the initial value from the array

2. Several important operations of the vector object, examples are as follows ：

(1) a.assign(b.begin(), b.begin() 3); //b is a vector, assign the vector composed of 0~2 elements of b to a

（2）a.assign(4,2); //A only contains 4 elements, and each element is 2

（3）a.back(); //Return a The last element of

(4) a.front(); //Return the first element of a

(5)a[i]; //Return the i-th element of a Element, if and only if a[i] exists2013-12-07

（6）a.clear(); //Clear the elements in a

（7）a.empty (); //Determine whether a is empty. If it is empty, it returns true, if it is not empty, it returns false

(8) a.pop_back(); //Delete the last element of a vector

(9) a.erase(a.begin() 1,a.begin() 3); //Delete the 1st (from 0th) to the 2nd element in a, that is to say, delete Elements count from a.begin() 1 (including it) to a.begin() 3 (excluding it)

(10) a.push_back(5); //At the last one of a Insert an element after the vector, its value is 5

(11) a.insert(a.begin() 1,5); //The first element of a (counting from the 0th) Insert the value 5 at the position, for example, a is 1,2,3,4, and after inserting the element, it is 1,5,2,3,4

(12) a.insert(a.begin() 1, 3,5); //Insert 3 numbers at the position of the first element of a (counting from the 0th one), and their values ​​are all 5

(13) a.insert(a.begin () 1,b 3,b 6); //b is an array, insert the 3rd element to the 5th element of b (excluding b) at the position of the 1st element of a (counting from 0th) 6), if b is 1,2,3,4,5,9,8, after inserting the element, it will be 1,4,5,9,2,3,4,5,9,8

( 14) a.size(); //Return the number of elements in a;

(15) a.capacity(); //Return the total number of elements that a can accommodate in memory

(16) a.resize(10); //Adjust the number of existing elements of a to 10, delete more elements, fill in fewer elements, and the values ​​are random

(17) a. resize(10,2); //Adjust the number of existing elements of a to 10, delete more elements, and fill in less elements. The value is 2

(18) a.reserve(100); //Expand the capacity of a to 100, which means that the return value when testing a.capacity(); is now 100. This operation only makes sense when a large amount of data needs to be added to a, because This will avoid multiple memory capacity expansion operations (the computer will automatically expand when the capacity of a is insufficient, of course, this will inevitably reduce performance)

(19) a.swap(b); //b is a vector, and The elements in a and the elements in b are exchanged as a whole

(20) a==b; //b is a vector, and the comparison operations of vectors are !=,>=,<=, >,<

3. Several ways to access vector sequentially. Examples are as follows:

(1) Add elements to vector a

 vector<int> a;
for(int i=0;i<10;i++)
a.push_back(i);

2. You can also Select elements from the array and add them to the vector

int a[6]={1,2,3,4,5,6};

vector b;

for(int i=1;i<=4;i )

b.push_back(a[i]);

3. You can also select elements from an existing vector Add

int a[6]={1,2,3,4,5,6};

vector b;

vector< to the vector int> c(a,a 4);

for(vector::iterator it=c.begin();it

b .push_back(*it);

4. You can also read elements from the file and add

ifstream in("data.txt");
vector<int> a;
for(int i; in>>i)
    a.push_back(i);

5 to the vector. [Misunderstanding]

vector<int> a;
for(int i=0;i<10;i++)
    a[i]=i;
//这种做法以及类似的做法都是错误的。刚开始我也犯过这种错误，后来发现，下标只能用于获取已存在的元素，而现在的a[i]还是空的对象

(2) From Reading elements in the vector

1. Reading through subscripts

int a[6]={1,2,3,4,5,6};
vector<int> b(a,a+4);
for(int i=0;i<=b.size()-1;i++)
    cout<<b[i]<<" ";

2. Reading through traversers

int a[6]={1,2,3,4,5,6};
vector<int> b(a,a+4);
for(vector<int>::iterator it=b.begin();it!=b.end();it++)
    cout<<*it<<" ";

4. Several important algorithms, use The header file needs to be included:

#include<algorithm>

(1) sort(a.begin(),a.end()); //From a.begin() (including it) to a. The elements of end() (excluding it) are arranged from small to large

(2)reverse(a.begin(),a.end()); //For the elements in a from a.begin() (including it) to a.end() (excluding it) Invert, but not arrange. For example, the elements in a are 1,3,2,4. After inversion, they are 4,2,3,1

(3) copy(a.begin(),a.end( ),b.begin() 1); //Copy the elements in a from a.begin() (including it) to a.end() (excluding it) to b, from b.begin() Start copying at the position of 1 (including it), overwriting the original elements

(4) find(a.begin(),a.end(),10); //From a. in a. begin() (including it) searches for 10 in the element of a.end() (excluding it), and if it exists, returns its position in the vector

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