c/c++ 数组和指针

c/c++ 数组和指针

知识点

1，数组就是指针，对应代码里的test1

2，用auto声明，得到的是指针，对应代码里的test2

3，用decltype声明，得到的不是指针 ，对应代码里的test3

4，用指针模拟end ，对应代码里的test4

5，标准库函数std::begin，std::end，对应代码里的test5

6，ptrdiff_t和size_t，ptrdiff是数组下标相加减的值的类型，size_t是数组下标的类型，对应代码里的test6

7，数组的下标可以是负值，标准库的string,vector的下标也可以是负值，对应代码里的test7

8，用数组初始化vector,注意生成的vector里的元素不包括第二个参数，对应代码里的test8

#include <iostream>#include <vector>using namespace std;int main(){  
//test1 数组就是指针                                                          
  /*                                                                            
  string ar[] = {"aa","bb"};                                                    
  string* p = ar;                                                               
  *p = "cc";                                                                    
  string* p1 = &ar[1];                                                          
  *p1 = "dd";                                                                   
  for(auto s : ar){                                                             
    cout << s;                                                                  
  }                                                                             
  cout << endl;                                                                 
  */

  //test2 用auto声明，得到的是指针                                              
  /*                                                                            
  int ia[] = {1,2,3,5};                                                         
  //ia1为整数指针                                                               
  auto ia1(ia);                                                                 
  *ia1 = 9;                                                                     
  auto ia2(&ia[3]);                                                             
  *ia2 = 8;                                                                     
  for(auto s : ia){                                                             
    cout << s << ",";                                                           
  }                                                                             
  cout << endl;                                                                 
  */

  //test3 用decltype声明，得到的不是指针                                        
  /*                                                                            
  int ia[3];                                                                    
  decltype(ia) ia3 = {2,3,4};                                                   
  //ia3 = &ia[0];//编译错误                                                     
  ia3[2] = 9;                                                                   
  for(auto s : ia3){                                                            
    cout << s << ",";                                                           
  }                                                                             
  cout << endl;                                                                 
  */

  //test4 用指针模拟end                                                         
  /*                                                                            
  int arr[] = {0,1,2};                                                          
  int* end = &arr[3];                                                           
  for(int* beg = arr;beg != end; ++ beg){                                       
    cout << *beg;                                                               
  }                                                                             
  cout << endl;                                                                 
  */

  //test5 标准库函数std::begin，std::end                                        
  /*                                                                            
  int arr[] = {0,1,2};                                                          
  int* beg = std::begin(arr);                                                   
  //int* end = &arr[3];                                                         
  int* end = std::end(arr);                                                     
  for(;beg != end; ++ beg){                                                     
    cout << *beg;                                                               
  }                                                                             
  cout << endl;                                                                 
  */

  //test6 ptrdiff_t和size_t                                                     
  //ptrdiff是数组下标相加减的值的类型，size_t是数组下标的类型                   
  /*                                                                            
  int arr[] = {1,2,3,4,5};                                                      
  int* b = std::begin(arr);                                                     
  int* e = std::end(arr);                                                       
  ptrdiff_t juli = e - b - 1;                                                   
  cout << juli << endl;                                                         
  size_t sz = juli;                                                             
  cout << arr[sz] << endl;                                                      
  */

  //test7 数组的下标可以是负值，标准库的string,vector的下标也可以是负值         
  /*                                                                            
  int ia[] = {1,2,3,4,5};                                                       
  int* p = &ia[2];                                                              
  int j = p[1];//相当于*(p + 1),也就是ia[3]                                     
  cout << j << endl;                                                           
  int k = p[-2];//相当于*(p - 2)，也就是ia[0]                                   
  cout << k << endl;                                                            
  string s("abcde");                                                            
  char* p1 = &s[2];                                                             
  cout << p1[-1] << endl;                                                       
  vector<int> v{1,2,3,4};                                                       
  int* p2 = &v[3];                                                              
  cout << p2[-2] << endl;                                                       
  */

  //test8 用数组初始化vector,注意生成的vector里的元素不包括第二个参数           
  /*                                                                            
  int ia[] = {0,1,2,3,4,5,6};                                                   
  vector<int> v(std::begin(ia), std::end(ia));                                  
  for(auto s : v){                                                              
    cout << s << ",";                                                           
  }                                                                             
  cout << endl;                                                                 
  vector<int> v1(ia + 1, ia + 4);                                               
  for(auto s : v1){                                                             
    cout << s << ",";                                                           
  }                                                                             
  cout << endl;                                                                 
  */}

 原文作者：小石王

原文链接：https://www.cnblogs.com/xiaoshiwang/p/9632499.html