C语言进阶课程学习记录-第28课 - 指针和数组分析（上）

数组

实验-指针加一

#include <stdio.h>

int main()
{
    int a[5] = {0};
    int* p = NULL;

    printf("a = 0x%X\n", (unsigned int)(a));
    printf("a + 1 = 0x%X\n", (unsigned int)(a + 1));

    printf("p = 0x%X\n", (unsigned int)(p));
    printf("p + 1 = 0x%X\n", (unsigned int)(p + 1));

    return 0;
}


/*
output:

a = 0x60FEE8
a + 1 = 0x60FEEC
p = 0x0
p + 1 = 0x4

a是数组首个元素的地址
a+1  ----> a+1*sizeof(*a)  a+1*sizeof(a[0])    a+4



*/

指针运算

实验-同一数组的指针相互运算

#include <stdio.h>

int main()
{
    char s1[] = {'H', 'e', 'l', 'l', 'o'};
    int i = 0;
    char s2[] = {'W', 'o', 'r', 'l', 'd'};
    char* p0 = s1;
    char* p1 = &s1[3];
    char* p2 = s2;
    int* p = &i;

    printf("%d\n", p0 - p1);
   //printf("%d\n", p0 + p2);//error: invalid operands to binary + (have 'char *' and 'char *')|
    //printf("%d\n", p0 - p2);//无意义
    //printf("%d\n", p0 - p);
    //printf("%d\n", p0 * p2);
    //printf("%d\n", p0 / p2);

    return 0;
}


/*
output:
-3




*/

实验-字符串与指针

#include <stdio.h>

#define DIM(a) (sizeof(a) / sizeof(*a))

int main()
{
    char s[] = {'H', 'e', 'l', 'l', 'o'};
    char* pBegin = s;
    char* pEnd = s + DIM(s); // Key point 指向最后一个元素的后面
    char* p = NULL;

    printf("pBegin = %p\n", pBegin);
    printf("pEnd = %p\n", pEnd);

    printf("Size: %d\n", pEnd - pBegin);

    for(p=pBegin; p<pEnd; p++)
    {
        printf("%c", *p);
    }

    printf("\n");

    return 0;
}


/*
output:
pBegin = 0060FEEF
pEnd = 0060FEF4
Size: 5
Hello


*/

小结

数组声明时编译器自动分配一片连续的内存空间
指针声明时只分配了用于容纳地址值的4字节空间
指针和整数可以进行运算，其结果为指针
指针之间只支持减法运算，其结果为数组元素下标差
指针之间支持比较运算，其类型必须相同