C++：STL的容器类&array的初步使用

什么是容器？

容器是用来存放对象的，就是容器类，是用做的容器的内存的管理方法
内核：数据结构 + 算法
C语言的数组和结构体，是语言源生支持的容器
C++ 的容器通过类库提供，容器类库被模板技术泛华后，就是STL容器
STL容器有哪些？
序列容器：位置与元素值无关；包括array、vector、deque、list、forward_list等几个。
排序容器：按照元素值排序好；包括set、multiset、map、mutilmap等。
哈希容器：未排序，元素位置由哈希函数决定；包括unordered_set、unordered_map、hash_set、hash_multiset、hash_map、hash_multimap等。

array的初步使用

array特点：定长、同类型元素、内存连续排布
本质是数组

1、构造、初始化

聚合初始化：从初始化器列表初始化聚合体。此为列表初始化的一种形式

#include <array>
#include <string>

void test070803(void) {
  std::array<int, 3> a0;
  std::array<int, 3> a1{4, 5, 6};
  std::array<int, 3> a2 = {1, 2, 3};  //聚合初始化
  std::array<int, 3> a3 = a2;         //拷贝初始化
}

2、元素访问

#include <array>
#include <string>

void test070803(void) {
  std::array<int, 3> a1{4, 5, 6};
  cout << "a1[0] = " << a1[0] << endl;
  cout << "a1[1] = " << a1[1] << endl;
  cout << "a1[2] = " << a1.operator[](2) << endl;
  a1[2] = 99;
  cout << "a1[2] = " << a1[2] << endl;

  cout << "a1.at(0)  = " << a1.at(0) << endl;

  a1.at(0) = 888;
  cout << "a1.at(0) = " << a1.at(0) << endl;

  // front和back方法返回第1个和最后1个元素
  cout << "a1.front() = " << a1.front() << endl;
  cout << "a1.back()  = " << a1.back() << endl;

  // data返回真实存储内存中首元素首地址的值
  cout << "a1.data() = " << a1.data() << endl;
  cout << "*(a1.data()) = " << *(a1.data()) << endl;
  cout << "*(a1.data()+1)= " << *(a1.data() + 1) << endl;
  cout << "*(a1.data()+2)= " << *(a1.data() + 2) << endl;
  int* p = a1.data();
  cout << " p= " << p << endl;
  cout << "*(a1.data()++)= " << *(p++) << endl;
  cout << " p= " << p << endl;
  cout << "*(a1.data()++)= " << *(p++) << endl;

  // empty
  cout << "a1.empty()= " << a1.empty() << endl;
  // size
  cout << "a1.size()= " << a1.size() << endl;
  // max_size
  cout << "a1.max_size() = " << a1.max_size() << endl;

操作
fill
swap

非成员函数
operator重载函数
get
swap
to_array

#include <algorithm>  // for std::swap
#include <array>      // for std::array
#include <stdexcept>  // for std::out_of_range

// Helper function to print array contents
template <typename T, std::size_t N>
void printArray(const std::array<T, N>& arr) {
  for (std::size_t i = 0; i < N; ++i) {
    std::cout << arr[i] << " ";
  }
  std::cout << std::endl;
}

int test070804() {
  std::array<int, 5> arr1;
  std::array<int, 5> arr2;

  // Fill arr1 with value 10 and arr2 with value 20
  arr1.fill(10);
  arr2.fill(20);

  // Print arrays before swapping
  std::cout << "Array 1 before swap: ";
  printArray(arr1);

  std::cout << "Array 2 before swap: ";
  printArray(arr2);

  // Swap the contents of arr1 and arr2
  swap(arr1, arr2);  //数据交换 内存没有改变

  // Print arrays after swapping
  std::cout << "Array 1 after swap: ";
  printArray(arr1);

  std::cout << "Array 2 after swap: ";
  printArray(arr2);

  // Use operator[] to access and modify elements
  arr1[2] = 50;
  std::cout << "Array 1 after modifying index 2: ";
  printArray(arr1);

  // Compare arrays using operator==
  if (arr1 == arr2) {  //比较长度和数据内容
    std::cout << "Array 1 is equal to Array 2" << std::endl;
  } else {
    std::cout << "Array 1 is not equal to Array 2" << std::endl;
  }

  // Compare arrays using operator<=
  if (arr1 <= arr2) {
    std::cout << "Array 1 is less than or equal to Array 2" << std::endl;
  } else {
    std::cout << "Array 1 is greater than Array 2" << std::endl;
  }
  std::array<int, 3> a{4, 5, 6};
  // 获取值：
  std::cout << '(' << get<0>(a) << ',' << get<1>(a) << ',' << get<2>(a)
            << ")\n";

  // 设置值：
  get<0, int, 3>(a) = 1;
  get<1>(a) = 2;
  get<2>(a) = 3;

  // 获取值：
  std::cout << '(' << get<0>(a) << ',' << get<1>(a) << ',' << get<2>(a)
            << ")\n";

  return 0;
}

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