嵌入式学习第十五天！（内存管理、链表）

1. 内存管理：

1. malloc

void *malloc(size_t size);

功能：申请堆区空间

参数：size：申请堆区空间的大小

返回值：返回获得的空间的首地址，失败返回NULL

2. free

void free(void *ptr);

功能：释放堆区空间

注意：

1.free只能释放堆区空间

2. 一个空间只能被free一次，对此free程序会崩溃

3. malloc需要和free搭配使用，如果只有malloc没有free会内存泄露

练习：要求申请堆区空间，将“hello world”存放到堆区空间，完成打印

#include <stdio.h>
#include <stdlib.h>
#include <string.h>int main(void)
{char *p = NULL;p = malloc(16);if(p == NULL){printf("failed\n");return -1;}strcpy(p, "Hello World");printf("%s\n",p);free(p);return 0;
}

2. 内存溢出：

内存溢出也称为内存越界

3. 内存泄露：

程序中malloc的空间没有被释放

4. 内存碎片：

由于频繁申请和释放，导致连续的空间分散成一些小的碎片空间，当malloc超过碎片空间时，则无法获得该空间（空间不连续），将这样的空间称为内存碎片

1. 链表

1. 链表的构建

typedef int DataType;typedef struct node
{DataType Data;struct node *pNext;
}LinkNode;LinkNode *CreateLinkList(void)
{LinkNode *pTmpNode = NULL;pTmpNode = malloc(sizeof(LinkNode));if(pTmpNode == NULL){return NULL;}pTmpNode->pNext = NULL;return pTmpNode;
}

2. 链表的插入（头插法）

int InsertHeadLinkList(LinkNode * phead, DataType TmpData)
{LinkNode *pTmpNode = NULL;pTmpNode = malloc(sizeof(LinkNode));if(pTmpNode == NULL){return -1;}pTmpNode->Data = TmpData;pTmpNode->pNext = phead->pNext;phead->pNext = pTmpNode;return 0;
}

3. 链表的输出

int ShowLinkList(LinkNode *phead)
{LinkNode *pTmpNode = NULL;pTmpNode = phead->pNext;while(pTmpNode != NULL){printf("%d ",pTmpNode->Data);pTmpNode = pTmpNode->pNext;}printf("\n");return 0;
}

4. 链表值的替换

int ReplaceData(LinkNode *phead, int OldData, int NewData)
{LinkNode *pTmpNode = NULL;pTmpNode = phead->pNext;while(pTmpNode != NULL){if(pTmpNode->Data == OldData){pTmpNode->Data = NewData;}pTmpNode = pTmpNode->pNext;}return 0;
}

5. 链表删除某个值

int DeleteLinkList(LinkNode *phead, DataType DeleteData)
{LinkNode *pPreNode = NULL;LinkNode *pTmpNode = NULL;pTmpNode = phead->pNext;pPreNode = phead;while(pTmpNode != NULL){if(pTmpNode->Data == DeleteData){pPreNode->pNext = pTmpNode->pNext;free(pTmpNode);pTmpNode = pPreNode->pNext;}else{pTmpNode = pTmpNode->pNext;pPreNode = pPreNode->pNext;}}
}

6. 链表的释放

int DestoryLinkList(LinkNode **pphead)
{LinkNode *pTmpNode = NULL;LinkNode *pFreeNode = NULL;pTmpNode = pFreeNode = *pphead;while(pTmpNode != NULL){pTmpNode = pTmpNode->pNext;free(pFreeNode);pFreeNode = pTmpNode;}*pphead = NULL;return 0;
}

作业：

1. 封装函数在链表中实现尾插法

#include <stdio.h>
#include <stdlib.h>typedef int DataType;
typedef struct node
{DataType Data;struct node *pNext;
}LinkList;LinkList *CreatLinkList()
{LinkList *pTmpNode = NULL;pTmpNode = malloc(sizeof(LinkList));if(pTmpNode == NULL){return NULL;}pTmpNode->pNext = NULL;return pTmpNode;}int InsertTailLinkList(LinkList *pHead, DataType NewData)
{LinkList *pTmpNode = NULL;LinkList *pPotNode = NULL;pPotNode = pHead;pTmpNode = malloc(sizeof(LinkList));if(pTmpNode == NULL){return -1;}pTmpNode->Data = NewData;pTmpNode->pNext = NULL;while(pPotNode->pNext != NULL){pPotNode = pPotNode->pNext;}pPotNode->pNext = pTmpNode;return 0;}int ShowLinkList(LinkList *pHead)
{LinkList *pTmpNode = NULL;pTmpNode = pHead->pNext;while(pTmpNode != NULL){printf("%d ", pTmpNode->Data);pTmpNode = pTmpNode->pNext;}printf("\n");return 0;
}int DestoryLinkList(LinkList **pphead)
{LinkList *pTmpNode = NULL;LinkList *pFreeNode = NULL;pTmpNode = pFreeNode = *pphead;while(pTmpNode != NULL){pTmpNode = pTmpNode->pNext;free(pFreeNode);pFreeNode = pTmpNode;}*pphead = NULL;return 0;
}int main(void)
{LinkList *linklist = NULL;linklist = CreatLinkList();InsertTailLinkList(linklist, 1);InsertTailLinkList(linklist, 2);InsertTailLinkList(linklist, 3);InsertTailLinkList(linklist, 4);InsertTailLinkList(linklist, 5);ShowLinkList(linklist);DestoryLinkList(&linklist);
}

2. 从终端接收一个字符，将字符串倒置后输出(用指针的方法)：

“how are you” > "you are how"

#include <stdio.h>int Reverse(char *pstr)
{char *phead = NULL;char *ptail = NULL;char tmp = 0;phead = ptail = pstr;while(*ptail != '\0'){ptail++;}ptail--;while(phead < ptail){tmp = *phead;*phead = *ptail;*ptail = tmp;phead++;ptail--;}return 0;
}int ReverseStr(char *pstr)
{char *phead = NULL;char *ptail = NULL;char *tmp1 = NULL;char *tmp2 = NULL;char tmp = 0;Reverse(pstr);phead = ptail = pstr;while(*pstr != '\0'){while(*ptail != ' ' && *ptail != '\0'){ptail++;}ptail--;tmp1 = phead;tmp2 = ptail;while(tmp1 < tmp2){tmp = *tmp1;*tmp1 = *tmp2;*tmp2 = tmp;tmp1++;tmp2--;}if (*ptail != '\0'){ptail = ptail + 2;phead = ptail;}else{break;}}}int main(void)
{char str[32] = "how are you";ReverseStr(str);printf("%s\n",str);return 0;
}