C++ <vector> pop_back function

C++ container class <vector>

Among the many container operations,pop_backis a very practical function, used toRemove the element at the end of the vector。

pop_backis a member function of container classes, used to delete the last element of the container. The container'ssize()Will decrease by 1.

pop_backImplemented the container'sDynamic shrinking, allowing you to remove trailing elements that are no longer needed at any time.

Word Definitions： popis to pop,backmeans "back", combined it means popping the element at the back, which is very vivid.

Basic syntax and parameters

pop_backis a member function of container classes, so you need to have a container object first, and then use the dot operator.to call it.

Syntax format

void pop_back();

Parameter description

  • Parameter: No parameters
    • pop_backaccepts no arguments.

Function description

  • Return Value： void(no return value). Its purpose is purely to "remove an element"; once the removal is done, the function ends.
  • Effect: of the containersize()(current number of elements) decreases by 1. The original last element is removed.
  • Note: If the container is empty, callingpop_backis undefined behavior. Before calling, you should first check whether the container is empty (usingempty()function).

Example

Let us thoroughly master it through a series of examples from simple to complex.pop_backUsage.

Example 1: Basic usage - removing the trailing element

Example

#include <iostream>
#include <vector> // 1. Must include the vector header file

int main() {
    // 2. Create a vector and add some elements
    std::vector<int> numbers = {10, 20, 30, 40, 50};

    std::cout << "Initially, the size of the vector is: " << numbers.size() << std::endl;
    std::cout << "The elements are: ";
    for(int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    // 3. Use pop_back to remove the last element
    numbers.pop_back(); // Delete the last element (50)
    std::cout << After deleting one element, the size is: << numbers.size() << std::endl;

    numbers.pop_back(); // Delete the last element (40)
    std::cout << After deleting another element, the size is: << numbers.size() << std::endl;

    // 4. Traverse and output all elements
    std::cout << The remaining elements are:;
    for(int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    return 0;
}

Expected run result:

初始时，vector的大小是: 5
元素是: 10 20 30 40 50
删除一个元素后，大小是: 4
再删除一个元素后，大小是: 3
剩余的元素是: 10 20 30

Code analysis:

  1. #include <vector>is to usevectorThe premise of the container.
  2. std::vector<int> numbers = {10, 20, 30, 40, 50};created a ... containing 5 elementsvector。
  3. twicepop_backcall, successively removed the trailing50and40。
  4. after each call, the container'ssize()Will all decrease by 1.

Example 2: Safe usage of pop_back - checking whether the container is empty

When callingpop_back, it is best to check whether the container is empty to avoid undefined behavior.

Example

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

int main() {
    // Create a vector that stores strings
    std::vector<std::string> tasks = {"Learn C++", "Do homework", "Read documentation"};

    std::cout << Number of todos: << tasks.size() << std::endl;

    // Safely delete the last element
    while(!tasks.empty()) {
        std::cout << Completed: << tasks.back() << std::endl;
        tasks.pop_back(); // Delete the last element
        std::cout << Remaining todos: << tasks.size() << std::endl;
    }

    // Try to delete again (the container is empty now)
    if(tasks.empty()) {
        std::cout << No more todos! << std::endl;
    }

    return 0;
}

Expected run result:

待办事项数量: 3
完成: 阅读文档
剩余待办事项: 2
完成: 写作业
剩余待办事项: 1
完成: 学习 C++
剩余待办事项: 0
没有更多待办事项了！

Code analysis:

  • !tasks.empty()checks whether the container is not empty.
  • tasks.back()returns the last element (without deleting it); it is used here to show what task has been completed.
  • UsagewhileLoop coordinationempty()check, you can safely clear the entire container.

Example 3: Implementing a simple stack using pop_back

push_backandpop_backUsed together, they can implement a simple stack structure.

Example

#include <iostream>
#include <vector>

class Stack {
private:
    std::vector<int> data;

public:
    // Push
    void push(int value) {
        data.push_back(value);
    }

    // Pop
    void pop() {
        if(!data.empty()) {
            data.pop_back();
        }
    }

    // Get the top element of the stack
    int top() {
        if(!data.empty()) {
            return data.back();
        }
        return -1; // Indicates the stack is empty
    }

    // Check if the stack is empty
    bool empty() {
        return data.empty();
    }

    // Get the size of the stack
    size_t size() {
        return data.size();
    }
};

int main() {
    Stack s;

    // Push operation
    s.push(10);
    s.push(20);
    s.push(30);

    std::cout << Stack size: << s.size() << std::endl;
    std::cout << Top element of stack: << s.top() << std::endl;

    // Pop operation
    s.pop();
    std::cout << After popping, the top element: << s.top() << std::endl;

    s.pop();
    std::cout << After popping again, the top element: << s.top() << std::endl;

    s.pop();
    std::cout << After popping again, is the stack empty: << (s.empty() ? Yes : No) << std::endl;

    return 0;
}

This example shows how to usepop_backto implement the stack's pop operation.push_backCorresponds to push,pop_backCorresponds to pop.

C++ container class <vector>

other extensions