STL notes (VI): container vector

STL note （ 6、 ... and ）： Containers ——vector

In this part , It mainly shows how to use containers , On the one hand, it is how to use the functions provided by each type of container in the standard template library , How to operate containers through these functions ; The other is how to use containers to solve some practical problems

Because the content of this part is too simple , Therefore, only the function of the corresponding container is given how to call , And examples of using these functions , And give a simple summary of some places prone to mistakes

In this part , Another important thing is to understand object-oriented programming ideas and methods , Compare it with the process oriented approach , Experience the difference between the two , Distinguish their strengths and weaknesses , Under what circumstances, what methods are applicable

vector Containers

function

#include <iostream>
#include <vector>
#include <string>

using namespace std;

//  General purpose container  - vector（ The dynamic array , Single port container ）

//  working principle ：
//  1.  Expand capacity 
//  2.  Copy the data 
//  3.  Additive element 

template <typename T>
class MyArray
{
private:
    T * pData;
    int length;
    int total;
public:
    MyArray(int n) {
        pData = new T[n];
        length = 0;
        total = n;
    }
    void Add(T value) {
        if (length < total) {
            pData[length++] = value;
        } else {
            total = total * 2; //  Double the length 
            T * temp = new T[total]; //  Create array 
            for (int i = 0; i < length; i++) { //  Copy the data 
                temp[i] = pData[i];
            }
            temp[length++] = value; //  Additive element 
            delete []pData; //  Release space 
            pData = temp; //  Copy the first address of the space 
        }
    }
    void Show() {
        for (int i = 0; i < length; i++) {
            cout << pData[i] << ' ';
        }
    }
    ~MyArray() {
        if (pData) {
            delete []pData;
            pData = NULL;
        }
    }
};

//  Definition 、 Initialization and traversal 
void Display(vector<int> v)
{
    for (vector<int>::iterator it = v.begin(); it != v.end(); it++) {
        cout << *it << ' ';
    }
    cout << endl;
}

void rDisplay(vector<int> v)
{
    for (vector<int>::reverse_iterator it = v.rbegin(); it != v.rend(); it++) {
        cout << *it << ' ';
    }
    cout << endl;
}

void test1()
{
    vector<int> v1;
    vector<int> v2(2); //  Number of spaces  - 2, Element number  - 2, The element value is 0
    vector<int> v3(3, 1); //  Number of spaces  - 3, Element number  - 3, Element value 1

    int a[3] = {10, 20, 30};
    vector<int> v4(a, a + sizeof(a)/sizeof(int));
    vector<int> v5(v4.begin(), v4.end()); //  Iterator construction 
    vector<int> v6(v5); //  Copy structure 

    Display(v6);
    rDisplay(v6);

    vector<int> v7 = v6;
    v2.swap(v6); //  In exchange for 
}

//  Access data 
void test2()
{
    //  In the data 
    vector<int> v;
    v.push_back(10);
    v.push_back(20);

    //  Reading data 
    cout << v[0] << endl; // 10
    cout << v.at(0) << endl; // 10 -  Detect out of bounds 
    cout << v.front() << endl; // 10
    cout << v.back() << endl; // 20
    cout << *(v.begin() + 1) << endl; // 20
}

//  Container size 
void test3()
{
    // max_size
    vector<int> v1;
    cout << v1.max_size() << endl; //  When the container capacity is 0 when , The maximum capacity that the system can provide 

    // size - capacity
    vector<int> v2(2);
    cout << v2.size() << endl; // 2
    cout << v2.capacity() << endl; // 2

    v2.push_back(8);
    cout << v2.size() << endl; // 3
    cout << v2.capacity() << endl; // 4

    Display(v2); // 0 0 8

    // resize
    v2.resize(10);
    cout << v2.size() << endl; // 10
    cout << v2.capacity() << endl; // 10
    Display(v2); // 0 0 8 0 0 0 0 0 0 0

    // reserve -  Retain 
    v2.reserve(10);
    cout << v2.size() << endl; // 3
    cout <<v2.capacity() << endl; // 10
    Display(v2); // 0 0 8
}

//  modify 
void test4()
{
    vector<int> v;
    v.push_back(10);
    v.push_back(20);

    v[0] = 30;
    *(v.begin() + 1) = 40;

    //  Return type  -  quote 
    cout << ++v[0] << endl; // 31
    cout << ++v.at(0) << endl; // 32
    cout << ++v.front() << endl; // 33
    cout << ++v.back() << endl; // 41
    cout << ++(*v.begin()) << endl; // 34
}

int main()
{
//    MyArray<int> arr(2);
//    arr.Add(1);
//    arr.Add(2);
//    arr.Add(3);
//    arr.Add(4);
//    arr.Add(5);
//    arr.Show();

//    test1(); //  Definition 、 Initialization and traversal 
//    test2(); //  Access data 
//    test3(); //  Container size 
//    test4(); //  Modifying elements 

    return 0;
}

Case study

#include <iostream>
#include <vector>
#include <string>

using namespace std;

void Display(vector<int> v)
{
    for (vector<int>::iterator it = v.begin(); it != v.end(); it++) {
        cout << *it << ' ';
    }
    cout << endl;
}

//  Insert and delete 
void test5()
{
    vector<int> v;

    //  Insert 
    v.push_back(10);
    v.push_back(20);
    v.insert(v.begin(), 5);
    v.insert(v.end(), 25); // 5 10 20 25
    v.insert(v.begin() + 2, 15); // 5 10 15 20 25
    Display(v);

    v.insert(v.begin(), 3, 0);
    Display(v);

    vector<int> temp(2); // 0 0
    temp.insert(temp.begin(), v.begin(), v.end());
    Display(temp);

    //  Delete 
    v.pop_back(); //  Delete the last element 
    Display(v); // 0 0 0 5 10 15 20
    v.erase(v.begin() + 3);
    Display(v); // 0 0 0 10 15 20
    v.erase(v.begin() + 3, v.begin() +5);
    Display(v); // 0 0 0 20
    v.clear();
}

// Vector Case study ： Student management system 
class Student {
private:
    string Sno; //  Student number 
    string Sname; //  full name 
    int Sage; //  Age 
public:
    Student(string no, string name, int age):Sno(no),Sname(name),Sage(age) {}
    string getSno()
    {
        return Sno;
    }
    void setSage(int infoModified)
    {
        Sage = infoModified;
    }
    void Show()
    {
        cout << Sno << '\t' << Sname << '\t' << Sage << endl;
    }
};

class StudentManagement {
private:
    vector<Student> students;
public:
    void insertStudent(Student s)
    {
        students.push_back(s);
    }
    vector<Student>::iterator serachStudentBySno(string key)
    {
        for (vector<Student>::iterator it = students.begin(); it != students.end(); it++) {
            if (it->getSno() == key) {
                return it;
            }
        }
        return students.end();
    }
    void removeStudentBySno(string key)
    {
        if (serachStudentBySno(key) != students.end()) {
            students.erase(serachStudentBySno(key));
        }
    }
    void modifyStudentSageBySno(string key, int infoModified)
    {
        if (serachStudentBySno(key) != students.end()) {
            serachStudentBySno(key)->setSage(infoModified);
        }
    }
    void displayStudents()
    {
        for (vector<Student>::iterator it = students.begin(); it != students.end(); it++) {
            it->Show();
        }
    }
    void displayStudent(vector<Student>::iterator pos)
    {
        pos->Show();
    }
};

int main()
{
    // test5();

    Student stu1("1001", "Reyn", 21);
    Student stu2("1002", "Lisa", 20);
    Student stu3("1003", "Lena", 22);

    StudentManagement studentsMS; // Students Manage System
    studentsMS.insertStudent(stu1);
    studentsMS.insertStudent(stu2);
    studentsMS.insertStudent(stu3);

    cout << endl << " To display all student information " << endl;
    studentsMS.displayStudents();
    cout << endl << " Query student information by student number " << endl;
    studentsMS.displayStudent(studentsMS.serachStudentBySno("1002"));
    cout << endl << " Remove student information with student ID " << endl;
    studentsMS.removeStudentBySno("1003");
    studentsMS.displayStudents();
    cout << endl << " Modify student information with student number " << endl;
    studentsMS.displayStudent(studentsMS.serachStudentBySno("1002"));
    studentsMS.modifyStudentSageBySno("1002", 21);
    studentsMS.displayStudent(studentsMS.serachStudentBySno("1002"));

    return 0;
}

summary

• vector In essence, it is a dynamic array , That is, when the container capacity is not enough to hold the next element , Expand the capacity of the container to accommodate more elements
• vector One possible way to implement the principle of dynamic arrays is , First expand the capacity of the container , Then copy the original data to a container with larger capacity , Then add the element to be added
• vector In the constructor of , If a certain space is initialized in advance , Then the number of elements is equal to the length of space , And its element values are all zero
• vector Get the return type of all element values , Basically, they are all references to elements , Therefore, the operation of self increase or self decrease can be used , Whether pre or post
• Object oriented programming methods , The most obvious difference between programming and process oriented programming is ： Object oriented is “ Take a step , Take a look ” The programming process of , That is, first build the required objects , When some properties or functions are needed, add corresponding programs to realize ; Process oriented is “ Everything is planned ” The programming process of , That is, before writing the program , Just put every variable in the program , Every logical relationship is designed , Then program directly

In the next article , We will introduce C++ In the container ——deque