指针
注意
int x = 5;
int y = 15;
swap(&x,&y);
void swap(int *a,int *b){
// a的值就是&x a就是x的内存地址
// *a 表示x的值
}
取地址操作符
&变量名
int i = 10;
cout << "i内存地址:" << &i << endl;
变量定义
类型 * 指针变量名
int *pointer1, *pointer2;
float *pointer3;
char *pointer4;
上面pointer1、pointer2是指针变量名 ，在变量名前加*，表示该变量是指针变量
// 将变量i的内存地址存放到指针变量pointer1
pointer1 = &i;
// 输出在指针变量中存储的地址
cout << pointer1 << endl;
// 访问指针中地址的值
cout << *pointer1 << endl;
demo1
int *pointer1, *pointer2;
int i = 10;
pointer1 = &i;
cout << "i内存地址:" << &i << endl;
cout << "pointer1保存的内存地址:" << pointer1 << endl;
cout << "pointer1指针的值:" << *pointer1 << endl;
特殊的值NULL
没有初始化的指针变量是危险的。如果在声明变量之后，找不到合适的地址进行初始化。
在这里我们引入一个特殊的地址--NULL。它的意思是空，即指针没有指向任何东西。比如
int *empty = NULL;
// 打印00000000
cout << "empty address :" << empty << endl;
注意:c++是区分大小写敏感的，NULL和null是不同的。所以在使用是必须大写。
*
*又称为间接引用操作符。其作用是获取指针所指向的变量或存储空间。间接引用的指针可以作为左值。
*指针变量名
demo2
int* pointer1, * pointer2;
int i = 10;
pointer1 = &i;
cout << "i内存地址:" << &i << endl;
cout << "pointer1保存的内存地址-i的内存地址:" << pointer1 << endl;
cout << "pointer1指针的值-i的值:" << *pointer1 << endl;
cout << "pointer1指针自己内存地址:" << &pointer1 << endl;
int** iptriptr = &pointer1;
// pointer指针的内存地址
cout << "iptriptr保存的内存地址-pointer1的内存地址:" << iptriptr << endl;
// 这里"pointer1存储的是i的内存地址
cout << "iptriptr指针的值-pointer1的值=i的存储地址:" << *iptriptr << endl;
i内存地址:006FFACC
pointer1保存的内存地址-i的内存地址:006FFACC
pointer1指针的值-i的值:10
pointer1指针自己内存地址:006FFAE4
iptriptr保存的内存地址-pointer1的内存地址:006FFAE4
iptriptr指针的值-pointer1的值=i的存储地址:006FFACC
常量指针、指针常量
指针常量: 指针指向地址是一定的，但其内容可以修改 int *const p
常量指针: 指针可以指向其他地址，但是内容不可以改变 const int *p， int const *p
把*读作指针 const读作常量
int aa = 10;
const int bb = 18;
// 指针常量 指针指向地址不能改变，值可以变
int* const pc = &aa;
cout << *pc << " " << pc << endl;
*pc = bb;
cout << *pc << " " << pc << endl;
// 常量指针 值不能改变 address可以变
const int *cp = &aa;
cout << *cp << " " << cp << endl;
cp = &bb;
cout << *cp << " " << cp << endl;
delete
double * p3 = new double[3];
p3[0] = 0.2;
p3[1] = 0.5;
p3[2] = 0.8;
cout << "p3[1] is " << p3[1] << ".\n";
p3 = p3+1; // 指向下一个元素的地址 指向第2个元素而不是第一个元素
cout << "now p3[0] is " << p3[0] << " and ";
cout << "p3[1] is " << p3[1] << ".\n";
p3 = p3-1; //将指针指向原来的值
delete [] p3; // free the memory
return 0;
demo
double wages[3] = {10000.0,20000.0,30000.0};
short stack[3] = {3,2,1};
cout << "----------------------------------------" << endl;
//pw声明只想double类型的指针,然后将它初始化为wages数组种的第一个元素的地址
double *pw = wages;
short *ps = &stack[0];
cout << "pw= " << pw << ",*pw= " << *pw <<endl;
pw=pw+1;
cout << "add 1 to the pw pointer:\n";
cout << "pw="<< pw << ",pw=" << *pw << "\n\n";
cout << "ps=" << ps << ",*ps=" << *ps << endl;
ps = ps+1;
cout << "add 1 to the ps pointer:\n";
cout << "ps=" << ps << ",*ps=" << *ps << "\n\n";
cout << "access two elements with array notation\n";
cout << "stack[0]=" << stack[0] << ",stack[1]=" << stack[1] << endl;
//stack[1]看作是*(stack+1)，这意味着先计算数组第2个元素的地址，然后找到存储在哪里的值
cout << "access two elements with pointer notation\n";
cout << "*stack="<< *stack << ",*(stack+1)=" << *(stack+1) << endl;
cout << sizeof(wages) << " = size of wages array\n";
cout << sizeof(pw) << " = size of pw pointer \n";
cout << "----------------------------------------" << endl;函数指针
函数返回值类型 (* 指针变量名) (函数参数列表);
#include <stdio.h>
int max(int x,int y);
int main(){
int (*p)(int a,int b);
int a, b, c;
//把函数max赋给指针变量p, 使p指向max函数
p = max;
printf("please enter a and b:");
scanf("%d%d", &a, &b);
c = (*p)(a,b); //通过函数指针调用max函数
printf("a = %d\nb = %d\nmax = %d\n", a, b, c);
return 0;
}
//定义max函数
int max(int x, int y) {
if (x >= y) {
return x;
}
else {
return y;
}
}
指针函数
//声明指针函数
int *add(int a,int b);
int main(){
int a = 5;
int b = 3;
//调用指针函数
int *c = add(a,b);
cout << "c.address="<< c<< endl;
return 0;
}
//定义指针函数
int *add(int a,int b){
int c=a+b;
// 返回变量c的内存地址
return &c;
}
demo
Animal animal;
animal.sleep();
Animal *a = new Animal;
a->age = 18;
a->setId(20);
cout << "getAge=" << a->getAge() << endl;
cout << "getId=" << a->getId() << endl;
打印指针地址
short dates[SS];
short * pti;
short index;
double bills[SS];
double * ptf;
pti = dates;
ptf = bills;
for(index =0; index<SS;index++) {
// 打印指针地址
printf("pointers.address=%p ptf.address=%p\n",pti+index,ptf+index);
}
pointers.address=000000000061FDFE ptf.address=000000000061FDD0
pointers.address=000000000061FE00 ptf.address=000000000061FDD8
pointers.address=000000000061FE02 ptf.address=000000000061FDE0
pointers.address=000000000061FE04 ptf.address=000000000061FDE8
pointers.address=000000000061FE06 ptf.address=000000000061FDF0
dates+2 == &dates[2] // 相同地址
*(dates+2) == dates[2] //相同值
*(dates+2) // 第3个元素
*dates + 2 // 第1个元素的值+2
