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C++基础：引用，内联函数，auto，类的两种定义方式

news 来源：原创 2025/5/14 15:09:48

#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;
int main()
{
   //权限缩小和放大的规则：适用于引用和指针
   //权限放大不能把const给非const，const只能给const
   const int a = 10;
   //int& b = a;//不行，权限放大
   const int& b = a;

   //权限缩小非const既可以给非const，也可以给const
   int c = 10;
   int& d = c;
   const int& e = c;

const int* cp1 = &a;
//int* p1 = cp1;//不能，属于权限的放大

int* cp2 = &c;
const int* p2 = cp2;//可以，属于权限的缩小

   //下面可以不跟上面的规则
   const int x = 10;
   int y = x;

   int z = 20;
   const int r = z;
   return 0;
}

&在类型前面是引用，在变量前面是取地址
1.引用做参数
void swap_c(int* p1, int* p2)
{
   int tmp = *p1;
   *p1 = *p2;
   *p2 = tmp;
}

void swap_cpp(int& r1, int& r2)//引用
{
   int tmp = r1;
   r1 = r2;
   r2 = tmp;
}

int main()
{
   int a = 1;
   int b = 0;
   swap_c(&a, &b);
   swap_cpp(a, b);
   return 0;
}

2.引用做返回值
int Count1()
{
   static int n = 0;
   n++;
   return n;
}

int& Count2()
{
   static int n = 0;
   n++;
   return n;
}

int main()
{
   const int& r1 = Count1();
   int& r2 = Count2();
   return 0;
}

int& Add(int a, int b)
{
static int c = a + b;//只会被执行一次
return c;
}

int& Add(int a, int b)
{
   static int c = 0;
   c = a + b;//这个时候会变成7
   return c;
}

int main()
{
   int& ret = Add(1, 2);
   Add(3, 4);
   cout << "Add(1, 2) is :" << ret << endl;
   return 0;
}

#include <time.h>
struct A
{
int a[10000];
};
void TestFunc1(A a)
{}

void TestFunc2(A& a)
{}
int main()
{
   A a;
   // 以值作为函数参数
   size_t begin1 = clock();
   for (size_t i = 0; i < 10000; ++i)
       TestFunc1(a);
   size_t end1 = clock();
   // 以引用作为函数参数
   size_t begin2 = clock();
   for (size_t i = 0; i < 10000; ++i)
       TestFunc2(a);
   size_t end2 = clock();
   // 分别计算两个函数运行结束后的时间
   cout << "TestFunc1(A)-time:" << end1 - begin1 << endl;
   cout << "TestFunc2(A&)-time:" << end2 - begin2 << endl;
   return 0;
}

引用和指针的区别
int main()
{
   int a = 10;
   int& b = a;
   int c = 10;
   b = c;

int* p = &a;
p = &c;

char c1 = 0;
char& c2 = c1;

char* p1 = &c1;
return 0;
}

int Add(int left, int right)
{
return left + right;
}

inline void Swap(int& x, int& y)
{
   int tmp = x;
   x = y;
   y = tmp;
}

//频繁调用Swap,调用函数需要栈帧，是有消耗的
//如何解决：1.C语言使用宏函数，2.C++使用内联函数
int main()
{
   int ret = Add(1, 2);
   int a = 1;
   int b = 2;
   Swap(a, b);
   return 0;
}

int main()
{
   int a = 0;
   auto b = a;//b的类型是根a的类型自动确定的
   int& c = a;
   auto& d = a;
   auto* p1 = &a;
   auto p2 = &a;

   cout << typeid(a).name() << endl;
   cout << typeid(b).name() << endl;
   cout << typeid(c).name() << endl;
   cout << typeid(d).name() << endl;
   cout << typeid(p1).name() << endl;
   cout << typeid(p2).name() << endl;

return 0;
}

int main()
{
   int array[] = { 1,2,3,4,5 };
   //C语言
   for (int i = 0; i < sizeof(array) / sizeof(array[0]); ++i)
   {
       array[i] *= 2;
   }

   for (int i = 0; i < sizeof(array) / sizeof(array[0]); ++i)
   {
       cout << array[i] << " ";
   }
   cout << endl;

   //C++
   for (auto& e : array)//因为array已经不是数组了
   {
       e *= 2;
   }

   for (auto e : array)
   {
       cout << e << " ";
   }
   cout << endl;

return 0;
}

void f(int)
{
   cout << "整形" << endl;
}
void f(int*)
{
   cout << "整型指针" << endl;
}
int main()
{
   //C
   int* p1 = NULL;

   //C++ 推荐下面这种写法
   int* p2 = nullptr;
   f(0);
   f(NULL);//预处理后f(0)
   f(nullptr);//f(void*()0)
   return 0;
}

class的默认访问权限为private，struct为public
class Student
{
   void ShowInfo()
   {
       cout << _name << endl;
       cout << _age << endl;
       cout << _stuid << endl;
   }
public:
   int GetAge()
   {
       return _age;
   }
//private:
   char _name;
   int _age;
   int _stuid;
};