[C/C++] 指针

指针的两种声明、初始化方式

1、直接声明

格式：typeName * pointerName = 内存地址;

//1.直接声明
int a = 10; // 声明变量a
int* pa = &a; // 声明int型指针pa，将a的地址指向pa
cout << "变量a的地址是&a=" << &a << endl;
cout << "指针pa指向地址是pa=" << pa << endl;
cout << "指针pa的值是*pa=" << *pa << endl;

2、new关键字声明指针

格式：typeName * pointerName = new typeName;

//2. new关键字声明指针
int* pa1 = new int;
char* pc = new char;
*pa1 = 100;
*pc = 'M';
cout << "指针pa1的值是*pa1=" << *pa1 << endl;
cout << "指针pc的值是*pc=" << *pc << endl;

3、使用sizeof来确定标准数据类型占用的字节数

#include "stdio.h"

int main()
{
    char c;
    short s;
    int i;
    long l;
    float f;
    double d;
    long double ld;
    int array[20];
    int *ptr = array;

    printf(" sizeof c = %d\t\tsizeof(char) = %d"
           "\n sizeof s = %d\t\tsizeof(short) = %d"
           "\n sizeof i = %d\t\tsizeof(int) = %d"
           "\n sizeof l = %d\t\tsizeof(long) = %d"
           "\n sizeof f = %d\t\tsizeof(float) = %d"
           "\n sizeof d = %d\t\tsizeof(double) = %d"
           "\n sizeof ld = %d\t\tsizeof(long double) = %d"
           "\n sizeof array = %d"
           "\n sizeof ptr = %d\n",
           sizeof c, sizeof(char),
           sizeof s, sizeof(short),
           sizeof i, sizeof(int),
           sizeof l, sizeof(long),
           sizeof f, sizeof(float),
           sizeof d, sizeof(double),
           sizeof ld, sizeof(long double),
           sizeof array, sizeof ptr);

    return 0;
}

输出结果：

 sizeof c = 1           sizeof(char) = 1
 sizeof s = 2           sizeof(short) = 2
 sizeof i = 4           sizeof(int) = 4
 sizeof l = 4           sizeof(long) = 4
 sizeof f = 4           sizeof(float) = 4
 sizeof d = 8           sizeof(double) = 8
 sizeof ld = 12         sizeof(long double) = 12
 sizeof array = 80
 sizeof ptr = 4