C++ Primer Plus 学习笔记第四章指针、数组和指针算数

梦里梦外; 2022-02-16 11:55 191阅读 0赞

double wages[3] = {10000.0, 20000.0, 30000.0};
      short stacks[3] = {3, 2, 1};
    
      double* pw = wages;
      short* ps = &stacks[0];

pw指向wages的第一个元素的内存地址

&wages指的是整个内存的地址。 所以 sizeof 返回的是整个数组的大小

short \*pas\[3\]指的是指针数组  数组里面全是指针

按照符号的优先级规则  pas会先跟\[\]结合 所以就是pas\[3\] 这是一个数组 它是short\*类型 这样写会更容易看  short\* pas\[3\]

short (\*pas)\[3\] 指的是数组指针  指向一个数组的指针

为了 便于区分  这样子能一目了然  short\* pas = new short\[3\];

解引用： \*pt = pt\[0\]    一个是指针表示法 一个是数组表示法

绝不要对未被初始化为适当地址的指针接触引用 。会炸

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如果需要限制strcpy()中字符串的长度 请使用 strncpy() 。

指针， 数组， 结构 指针数组 数组指针和指针的指针，auto类型的综合例子：

#include <iostream>
    
    struct antarctica_years_end
    {
      int year;
    };
    
    int main()
    {
      antarctica_years_end s01, s02, s03;
      s01.year = 1998;
      antarctica_years_end* pa = &s02;
      pa->year = 1999;
      antarctica_years_end trio[3];
      trio[0].year = 2003;
      std::cout << trio -> year << std::endl;
      const antarctica_years_end* arp[3] = {&s01, &s02, &s03};
      std::cout << arp[1]->year << std::endl;
      const antarctica_years_end** ppa = arp;
      auto ppb = arp;
      std::cout << (*ppa)->year << std::endl;
      std::cout << (*(ppb+1)) ->year << std::endl;
      return 0;
    }

模板类：vector： vector<typeName> vt(n\_elem); 包含在 std中 需要添加<vector>头文件 堆中

模板类：array: array<typeName, n\_elem> arr; 存储在栈中 <array>

模板类的例子：

#include <iostream>
    #include <vector>
    #include <array>
    
    int main()
    {
      using namespace std;
      double a1[4] = {1.2, 2.4, 3.6, 4.8};
      vector<double> a2(4);
      a2[0] = 1.0/3.0;
      a2[1] = 1.0 /5.0;
      a2[2] = 1.0/7.0;
      a2[3] = 1.0/9.0;
    
      array<double, 4> a3 = {3.14, 2.72, 1.62, 1.41};
      array<double, 4>a4;
      a4 = a3;
      
      cout << "a1[2]: " << a1[2] << " at " << &a1[2] << endl;
      cout << "a1[1]: " << a1[1] << " at " << &a1[1] << endl;
      cout << "a1[0]: " << a1[0] << " at " << &a1[0] << endl;
    // 用-4 然后就到了 a3的内存地址中去了
      cout << "a1[-4]: " << a1[-4] << " at " << &a1[-4] << endl;
      cout << "a2[2]: " << a2[2] << " at " << &a2[2] << endl;
      cout << "a3[2]: " << a3[2] << " at " << &a3[2] << endl;
      cout << "a4[2]: " << a4[2] << " at " << &a4[2] << endl;
    
      a1[-2] = 20.2;
      cout << "a1[-2]: " << a1[-2] << " at " << &a1[-2] << endl;
      cout << "a3[2]: " << a3[2] << " at " << &a3[2] << endl;
      cout << "a4[2]: " << a4[2] << " at " << &a4[2] <<endl;
    
      return 0; 
    }

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第四章完结。 明天开始学第五章

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