二级指针

二级指针做函数输出特性

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int getMem(char ** p) {
    if (p == NULL)
    {
        return -1;
    }
    
    char *tmp = (char *)malloc(sizeof(char) * 100);
    if (tmp == NULL)
    {
        return -2;
    }
    strcpy(tmp, "hello world");
    *p = tmp;
    return 0;
}

int main() {
    char * p = NULL;
    int ret = 0;
    ret = getMem(&p);
    if (ret != 0)
    {
        printf("getMem error..\n");
        return ret;
    }
    printf("p = %s\n", p); //p = hello world
    if (p != NULL)
    {
        free(p);
    }
    
    return 0;
}

指针数组的使用

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    char * p1 = "aaaaa";
    char * p2 = "bbbbb";
    char * p3 = "ccccc";
    char * p4 = "ddddd";

    //指针数组，每个元素都是一个char * 类型
    char *arr[] = {"aaaaa", "bbbbb", "ccccc", "ddddd"};
    int n = sizeof(arr) / sizeof(arr[0]);
    for (size_t i = 0; i < n; i++)
    {
        printf("%s\n", arr[i]);
    }
    return 0;
}

一维数组

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    int a[] = {1, 2, 3, 4}; // 4个元素
    int b[100] = {1, 2, 3, 4}; //没有赋值的都是0

    int n = sizeof(a) / sizeof(a[0]);
    for (size_t i = 0; i < n; i++)
    {
        // printf("%d  ", a[i]);
        // a+i代表第i个元素的地址
        printf("%d  ", *(a+i)); //1  2  3  4  
    }
    return 0;
}