C++ <list> push_front function
push_frontis used in list toadd an element at the head of the linked listThe function is one of the signature operations of a linked list.
push_frontis a member function used tolinked list (list)ofheaderadd a new element.
Unlike vector,listThe time complexity of inserting an element at the head is O(1), which is very efficient.
Word Definitions： pushis pushing,frontIt means "front"; combined together, it means "push to the front," which is very vivid.
Basic syntax and parameters
push_frontIt is a member function of the container class, and calling it requires no arguments.
Syntax format
void push_front(const T& value); void push_front(T&& value); // C++11 之后（支持右值）
Parameter description
- Parameter：
value- Type: same as the element type specified when the container is defined.
- Description: the value you want to add to the head of the container.
Function description
- Return Value：
void(no return value). - Effect: of the container
size()It will increase by 1. The new element becomes the first element of the linked list.
Example
Let's thoroughly master it through examples.push_frontUsage.
Example 1: Basic usage - adding an element at the head.
Example
#include <iostream>
#include <list>
int main() {
std::list<int> numbers = {20, 30, 40};
std::cout << "original list: ";
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
// Add an element at the front
numbers.push_front(10);
std::cout << After push_front(10):;
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
#include <list>
int main() {
std::list<int> numbers = {20, 30, 40};
std::cout << "original list: ";
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
// Add an element at the front
numbers.push_front(10);
std::cout << After push_front(10):;
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
Expected output:
原始 list: 20 30 40 push_front(10) 后: 10 20 30 40
Code analysis:
push_front(10)Add 10 to the head of the linked list, making it the first element.Example 2: Building a linked list
Usagepush_frontIt is convenient to build a linked list from the head.
Example
#include <iostream>
#include <list>
int main() {
std::list<int> data;
// Add to the head sequentially; the final order is opposite to the insertion order.
data.push_front(5);
data.push_front(4);
data.push_front(3);
data.push_front(2);
data.push_front(1);
std::cout << Constructed linked list:;
for(int n : data) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
#include <list>
int main() {
std::list<int> data;
// Add to the head sequentially; the final order is opposite to the insertion order.
data.push_front(5);
data.push_front(4);
data.push_front(3);
data.push_front(2);
data.push_front(1);
std::cout << Constructed linked list:;
for(int n : data) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
Expected output:
构建的链表: 1 2 3 4 5
Code analysis:
- Each time
push_frontBoth add new elements to the head. - The final linked list order is 1 -> 2 -> 3 -> 4 -> 5.
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