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1. Vector container initialization
1. Vector container initialization
The vector container is a dynamic array container in the C++ Standard Template Library (STL). The container has the following initialization method:
- Default initialization: Create an empty vector container; the container is empty by default;
// 创建一个空的 vector 容器 , 元素类型是 int 类型
vector<int> vec;
- Use std::initializer_list to initialize the list: when creating a vector container, directly specify the element value;
// 创建一个 vector 容器 , 元素类型是 int 类型
// 为其初始化 1, 2, 3 三个元素值
vector<int> vec {
1, 2, 3};
- Use array initialization: Pass an array and the number of arrays to the vector container constructor to initialize the vector container.
// 先声明一个数组
int array[] = {
1, 2, 3, 4, 5};
// 将整个数组的值 初始化给 vector 容器
vector<int> vec(array, array + sizeof(array) / sizeof(int));
- Use iterator range initialization: specify the range of elements to be copied by passing two iterators;
// 初始化一个 vector 容器
vector<int> vec1 {
1, 2, 3};
// 使用 范围构造函数 从 vec1 容器中 复制元素到 vec2 容器
vector<int> vec2(vec1.begin(), vec1.end());
2. Use std::initializer_list initialization list to initialize the vector container
In the previous parameterized constructor, several vector initialization methods were introduced, here
std::initializer_listIt is a template class introduced in C++11, which is used to initialize container objects;
Very useful if you need to initialize an std::vectoror std::list container with a set of values;std::initializer_list
To use std::initializer_listthe initialized vector container, you can declare it first std::initializer_list, and then use the declared std::initializer_listinitialized vector container; the following code example:
// 声明 initializer_list
std::initializer_list<int> initList = {
1, 2, 3, 4, 5};
// 使用 initializer_list 初始化 vector
std::vector<int> vec(initList);
You can also specify it directly during initialization std::initializer_list;
// 使用 initializer_list 初始化 vector
// 下面两种方式是等价的
std::vector<int> vec5{
1, 2, 3, 4, 5 };
std::vector<int> vec6 = {
1, 2, 3, 4, 5 };
3. Code example - vector container initialization
Code example:
#include "iostream"
using namespace std;
#include "vector"
// 自定义类
class Student{
};
int main() {
// 1. 默认初始化
// 创建一个空的 vector 容器 , 元素类型是 int 类型
vector<int> vec;
// 2. 创建一个 vector 动态数组容器
// 该容器中 有 3 个元素 , 每个元素值为 int 类型值 1
vector<int> vec1(3, 1);
// 3. 使用 范围构造函数 从 vec1 容器中 复制元素到 vec2 容器
vector<int> vec2(vec1.begin(), vec1.end());
// 4. 使用 拷贝构造函数 创建 vec3 容器
// 将其初始化为 vec1 的副本
vector<int> vec3(vec1);
// 5. 使用初始化列表初始化
// 声明 initializer_list
std::initializer_list<int> initList = {
1, 2, 3, 4, 5 };
// 使用 initializer_list 初始化 vector
std::vector<int> vec4(initList);
// 6. 使用初始化列表初始化
// 使用 initializer_list 初始化 vector
// 下面两种方式是等价的
std::vector<int> vec5{
1, 2, 3, 4, 5 };
std::vector<int> vec6 = {
1, 2, 3, 4, 5 };
// 控制台暂停 , 按任意键继续向后执行
system("pause");
return 0;
};
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2. Vector container assignment
When the vector container is initialized, the initialization value can be set, which has been discussed in the previous chapter;
After the vector container is initialized, if you want to modify the contents of the vector container,
- In addition to assignment,
- You can also add and delete elements, such as: insert to insert elements, push_back to add elements at the end, etc.;
In this chapter, we mainly discuss the assignment situation after initialization;
1. Vector container assignment method
vector container assignment method:
- assign function assignment: clear all elements in the container and fill the container with newly allocated elements; n represents the number of elements to be allocated, and val represents the element value to be allocated;
void assign(size_type n, const value_type& val);
// 1. 将 vec2 容器中的值替换为 3 个 int 类型数据 8
vector<int> vec2;
vec2.assign(3, 8);
- assign function assignment: clear all elements in the container and fill the container with newly allocated elements; first and last are iterators, indicating the range of elements to be allocated;
void assign(InputIt first, InputIt last);
// 2. 将 vec3 容器中的值替换为 vec1 容器中的 指定范围数据
vector<int> vec3;
vec3.assign(vec1.begin(), vec1.end());
- The swap function exchanges data: exchanges the data in this vector container with the data in other containers;
void swap(vector& other);
// 3. 将 vec1 与 vec2 容器中的数据进行交换
vec1.swap(vec2);
- Overload the equal sign operator function: use the equal sign operator of the vector container to assign the contents of another vector container to the current container;
vector& operator=(const vector& vec);
// 4. 使用重载等号操作符函数 进行赋值
vector<int> vec4;
vec4 = vec1;
2. Code example - vector container assignment
Code example:
#include "iostream"
using namespace std;
#include "vector"
// 自定义类
class Student{
};
int main() {
// 创建一个 vector 容器 , 使用初始化列表进行初始化
vector<int> vec1{
1, 2, 3, 4, 5 };
// 1. 将 vec2 容器中的值替换为 3 个 int 类型数据 8
vector<int> vec2;
vec2.assign(3, 8);
// 2. 将 vec3 容器中的值替换为 vec1 容器中的 指定范围数据
vector<int> vec3;
vec3.assign(vec1.begin(), vec1.end());
// 3. 将 vec1 与 vec2 容器中的数据进行交换
vec1.swap(vec2);
// 4. 使用重载等号操作符函数 进行赋值
vector<int> vec4;
vec4 = vec1;
// 控制台暂停 , 按任意键继续向后执行
system("pause");
return 0;
};
Results of the :
