二级指针内存模型（一）

二级指针做输入

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

int getMem(char **myp1,int *mylen1,char **myp2,int *mylen2)
{
    char *tmp1 = NULL;
    char *tmp2 = NULL;
    tmp1 = (char *)malloc(100);
    if(tmp1 == NULL)
    {
        return -1;
    }
    strcpy(tmp1,"abcdefg");
    *mylen1 = strlen(tmp1);
    *myp1 = tmp1;


    tmp2 = (char *)malloc(100);
    if(tmp2 == NULL)
    {
        return -1;
    }
    strcpy(tmp2,"abcdefg");
    *mylen2 = strlen(tmp2);
    *myp2 = tmp2;

    return 0;
}

int getMem_free(char **myp1)
{
    char *tmp = NULL;
    if(myp1 == NULL)
    {
        return;
    }
    tmp = *myp1;
    free(tmp);

    *myp1 = NULL;
    return 0;
}


int main()
{
    char *p1 = NULL;
    int len1 = 0;

    char *p2 = NULL;
    int len2 = 0;

    int iRet = 0;

    iRet = getMem(&p1,&len1,&p2,&len2);

    printf("p1 : %s \n",p1);
    printf("p2 : %s \n",p2);

    getMem_free(&p1);
    getMem_free(&p2);

    return 0;
}

二级指针做输入，利用指针改变指针指向内容

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

void printMyarray(char **myArray,int num)
{
    int i;
    for(i = 0; i < num; i++)
    {
        //printf("%s \n",myArray[i]);
        printf("%s \n",*(myArray+i));
    }
}

void sortMyarray(char **myArray,int num)
{
    int i = 0, j = 0;
    char *tmp = NULL;

    for(i = 0; i < num; i++)
    {
        for(j = i; j < num; j++)
        {
            if(strcmp(myArray[i],myArray[j]) > 0)
            {
                tmp = myArray[i];
                myArray[i] = myArray[j];
                myArray[j] = tmp;
            }
        }
    }
}

int main()
{
    int i = 0, j = 0;
    int num = 0;
    char *myArray[] = {"aaaaa","bbbbb","ccccl","1111111"};
    num = sizeof(myArray)/sizeof(myArray[0]);

    printMyarray(myArray,num);

    sortMyarray(myArray,num);

    printf("after sort\n");

    printMyarray(myArray,num);

    return 0;
}

如果将main函数中的字符串数组声明修改为

       char myArray[10][30] = {"aaaaa","bbbbb","ccccl","1111111"};

此时，在传入打印和排序的函数中仍然使用char ** myArray 来声明形参的话，会出现报错，原因是指针的步长不一样，而且指针指向的内存空间数据类型也不一样。