二级指针的3种内存模型

xiaoxiao2022-06-29 29

1.二级指针第一种内存模型

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> int sort_arr(char**myArr,int num) { char*temp; char **p = myArr; int i,j; for (i=0;i<num;i++) { for (j=i+1;j<num;j++) { if (strcmp(p[i],p[j])>0) { temp = p[i];//主意我们交换的只是指针的值，改变指针的指向 p[i] = p[j]; p[j] = temp; } } } return 0; } int print_arr(char**myArr,int num) { int i = 0; for (i=0;i<num;i++) { printf("num:%s\n",*(myArr+i)); } return 0; } int main() { //数组数组中的每一个元素是指针，指针数组 //1.排序 2.指针做函数参数 3.内存 int num,i,j; char*temp; char* myArr[4]={"ddd","cccc","bbbb","aaaaaaa"}; print_arr(myArr,4); sort_arr(myArr,4); printf("----------\n"); print_arr(myArr,4); system("pause"); return 0; }

2.二级指针第二种内存模型

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> int sort_arr(char myArr[10][20],int num) { char temBuf[20]; //char **p = myArr; int i,j; for (i=0;i<num;i++) { for (j=i+1;j<num;j++) { if (strcmp(myArr[i],myArr[j])>0) { strcpy(temBuf , myArr[i]);//把数据交换内存块 strcpy(myArr[i] , myArr[j]); strcpy(myArr[j] , temBuf); } } } return 0; } /* //第一种内存模型打印函数不适用第二种内存模型 //原因:二级指针做输入_第一种内存模型 myArr + 1 与第二种内存模型 myArr + 1 //指针步长不一样哈指针所指向内存空间的数据不一样 int print_arr(char**myArr,int num) { int i = 0; for (i=0;i<num;i++) { printf("num:%s\n",*(myArr+i)); } return 0; }*/ int print_arr(char myArr[10][20],int num) { int i = 0; for (i=0;i<num;i++) { printf("num:%s\n",*(myArr+i)); } return 0; } int main() { //数组数组中的每一个元素是指针，指针数组 //1.排序 2.指针做函数参数 3.内存 char temBuf[30]; char myArr[10][20]={"ff","bbbbb","ddddd","ccccc","eeeee"}; int num = 5; print_arr(myArr,num); sort_arr(myArr,num); printf("---------\n"); print_arr(myArr,num); system("pause"); return 0; }

3.二级指针第三种内存模型

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> //在堆上分配内存空间通过return返回 char** getMen(int num) { char **p = NULL; int i,j; p = (char **)malloc(sizeof(char*)*num); for (i =0;i<num;i++) { p[i] = (char*)malloc(sizeof(char)*100); sprintf(p[i],"%d%d%d",9-i,9-i,9-i);//向内存空间写入数据 } return p; } //在堆上分配内存空间，通过函数参数返回 int getMen2(char ***p,int num) { char **tmp = NULL; int i,j; tmp = (char **)malloc(sizeof(char*)*num); if (p==NULL) { return -1; } for (i =0;i<num;i++) { tmp[i] = (char*)malloc(sizeof(char)*100); sprintf(tmp[i],"%d%d%d",9-i,9-i,9-i);//向内存空间写入数据 } *p = tmp;// int a ; int *p ; p = &a; *p=10 ;通过三级指针修改二级指针的值 return 0; } //释放内存空间 int freeMen(char**p,int num) { int ret =0,i; for (i =0;i<num;i++) { if (p[i]!=NULL) { free(p[i]); p[i]=NULL; } } if (p!=NULL) { free(p); p=NULL; } return ret; } //打印 int print_arr(char**myArr,int num) { int i = 0; for (i=0;i<num;i++) { printf("num:%s\n",*(myArr+i)); } return 0; } //排序只交换指针 int sort_arr(char**myArr,int num) { char*temp; char **p = myArr; int i,j; for (i=0;i<num;i++) { for (j=i+1;j<num;j++) { if (strcmp(p[i],p[j])>0) { temp = p[i];//主意我们交换的只是指针的值，改变指针的指向 p[i] = p[j]; p[j] = temp; } } } return 0; } //排序2 交换数据 int sort_arr2(char**myArr,int num) { char temBuf[20]; char **p = myArr; int i,j; for (i=0;i<num;i++) { for (j=i+1;j<num;j++) { if (strcmp(p[i],p[j])>0) { strcpy(temBuf,p[i]);//交换数据 strcpy(p[i] , p[j]); strcpy(p[j] , temBuf); } } } return 0; } int main() { //1.排序 2.指针做函数参数 3.内存 char **p = NULL; //p = getMen(5); getMen2(&p,5); //排序前打印 print_arr(p,5); //排序 sort_arr2(p,5); //排序后打印 print_arr(p,5); //释放内存 freeMen(p,5); p=NULL; system("pause"); return 0; }

4.二级指针三种内存模型图：

5.二级指针强化练习（两个辅助指针变量挖字符串）

1)使用第二种内存模型主调函数分配内存

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> /*函数功能根据字符c来分割字符串str*/ int splitStr(const char *str,char c ,char buf[10][20],int *num) { char* p = NULL,*pTmp = NULL;//两个辅助指针变量 int tmpcount = 0,len; p = str; pTmp = str; do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { strncpy(buf[tmpcount],pTmp,p-pTmp); buf[tmpcount][p-pTmp] = '\0'; //printf("%s\n",buf[tmpcount]); tmpcount++; pTmp = p = p+1; len = strlen(p);//用来保存最后一个字符串的长度 } } else { //拷贝最后一个分割的字符串包括\0 strncpy(buf[tmpcount],pTmp,len+1); break; } } while (*p!='\0'); *num=tmpcount+1; return 0; } /*函数功能打印二维数组*/ void printArr(char a[10][20],int n) { int i; for (i=0;i<n;i++) { printf("%s\n",*(a+i)); } } int main() { char *input="abcdefg,hjkln,sssss,kkk,hhh,j"; char ctemp = ','; char myArr[10][20]={0}; char *tmp; int ret; int n,i; ret = splitStr(input,ctemp,myArr,&n); if (ret!=0) { printf("error\n"); } printArr(myArr,n); system("pause"); return 0; }

2)使用第三种内存模型主调函数分配内存

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> /*第三种内存模型*/ int splitStr(const char *str,char c,char **buf,int *count) { char* p = NULL,*pTmp = NULL;//两个辅助指针变量 int tmpcount = 0,len; p = str; pTmp = str; do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { strncpy(buf[tmpcount],pTmp,p-pTmp); buf[tmpcount][p-pTmp] = '\0'; //printf("%s\n",buf[tmpcount]); tmpcount++; pTmp = p = p+1; len = strlen(p);//用来保存最后一个字符串的长度 } } else { //拷贝最后一个分割的字符串包括\0 strncpy(buf[tmpcount],pTmp,len+1); break; } } while (*p!='\0'); *count=tmpcount+1; return 0; } int main() { char *input="abcdefg,hjkln,sssss,kkk,hhh,j"; char ctemp = ','; char **p = NULL; int ret; int n,i; p=(char**)malloc(10*sizeof(char*)); if (p==NULL) { return; } for (i=0;i<10;i++) { p[i] = (char *)malloc(20*sizeof(char)); } ret = splitStr(input,ctemp,p,&n); if (ret!=0) { printf("error\n"); } for (i=0;i<n;i++) { printf("%s\n",*(p+i)); } //释放内存 system("pause"); return 0; }

3）使用第三种内存模型被调函数分配内存通过return返回

#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> /*第三种内存模型被调函数分配内存通过return返回*/ char** splitStr2(char *str,char c,int *count) { char* p = NULL,*pTmp = NULL;//两个辅助指针变量 int tmpcount = 0,len,len2; char**buf; p = str; pTmp = str; //第一遍扫描开辟第一维空间 do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { tmpcount++; pTmp = p = p+1; } } else { break; } } while (*p!='\0'); *count=tmpcount+1; buf = (char**)malloc((tmpcount+1)*sizeof(char*)); //printf("tmpcount:%d\n",tmpcount); if(buf==NULL) { return NULL; } //第二遍扫描根据分割的字符串的长度，开辟第二维空间并拷贝字符串 tmpcount = 0; p = str; pTmp = str; do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { len = p-pTmp+1; buf[tmpcount] = (char*)malloc(len*sizeof(char)); if (buf[tmpcount] == NULL) { free(buf); return ; } strncpy(buf[tmpcount],pTmp,p-pTmp); buf[tmpcount][p-pTmp] = '\0'; tmpcount++; pTmp = p = p+1; len2 = strlen(p);//用来保存最后一个字符串的长度 } } else { //printf("tmpcount:%d\n",tmpcount); //printf("len2:%d\n",len2); buf[tmpcount] = (char*)malloc((len2+1)*sizeof(char)); if (buf[tmpcount] == NULL) { free(buf); return ; } //拷贝最后一个分割的字符串包括\0 strncpy(buf[tmpcount],pTmp,len2+1); break; } } while (*p!='\0'); return buf; } int main() { char *input="abcdefg,hjkln,sssss,kkk,hhh,j"; char ctemp = ','; char **p = NULL; int ret; int n,i; p = splitStr2(input,ctemp,&n); printf("n:%d\n",n); for (i=0;i<n;i++) { printf("%s\n",*(p+i)); } //释放内存空间 system("pause"); return 0; }

4）使用第三种内存模型被调函数分配内存通过函数参数返回

<pre name="code" class="cpp">#include<stdio.h> #include<stdlib.h> #include <string.h> #include <ctype.h> /*第三种内存模型被调函数分配内存通过tmpbuf返回*/ int splitStr3(char *str,char c,char*** tmpbuf,int *count) { char* p = NULL,*pTmp = NULL;//两个辅助指针变量 int tmpcount = 0,len,len2; char**buf; p = str; pTmp = str; //第一遍扫描开辟第一维空间 do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { tmpcount++; pTmp = p = p+1; } } else { break; } } while (*p!='\0'); *count=tmpcount+1; buf = (char**)malloc((tmpcount+1)*sizeof(char*)); //printf("tmpcount:%d\n",tmpcount); if(buf==NULL) { return -1; } //第二遍扫描根据分割的字符串的长度，开辟第二维空间并拷贝字符串 tmpcount = 0; p = str; pTmp = str; do { p = strchr(p,c); if (p!=NULL) { if (p-pTmp>0) { len = p-pTmp+1; buf[tmpcount] = (char*)malloc(len*sizeof(char)); if (buf[tmpcount] == NULL) { free(buf); return -2; } strncpy(buf[tmpcount],pTmp,p-pTmp); buf[tmpcount][p-pTmp] = '\0'; tmpcount++; pTmp = p = p+1; len2 = strlen(p);//用来保存最后一个字符串的长度 } } else { //printf("tmpcount:%d\n",tmpcount); //printf("len2:%d\n",len2); buf[tmpcount] = (char*)malloc((len2+1)*sizeof(char)); if (buf[tmpcount] == NULL) { free(buf); return -2; } //拷贝最后一个分割的字符串包括\0 strncpy(buf[tmpcount],pTmp,len2+1); break; } } while (*p!='\0'); *tmpbuf = buf; return 0; } //释放内存空间 void freeMem(char**p,int count) { int i =0; if (p == NULL) { return ; } for (i=0;i<count;i++) { if (p[i]!=NULL) { free(p[i]); } } if (p!=NULL) { free(p); } } int main() { char *input="abcdefg,hjkln,sssss,kkk,hhh,j"; char ctemp = ','; char **p = NULL; int ret; int n,i; ret = splitStr3(input,ctemp,&p,&n); if (ret!= 0) { printf("error"); return -1; } //printf("n:%d\n",n); for (i=0;i<n;i++) { printf("%s\n",*(p+i)); } //释放内存 freeMem(p,n); system("pause"); return 0; }

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