C语言中内存管理规范

一、内存申请

       1.建议使用calloc申请内存，尽量不要使用malloc。

      　calloc在动态分配完内存后，自动初始化该内存空间为零，而malloc不初始化，里边数据是随机的垃圾数据。

       2.申请内存大小必须大于0.

 　　 (1)使用0字节长度申请内存的行为是没有定义的，在引用内存申请函数返回地址时会引发不可预知错误，对于可能出现申请0长度内存的情况非常有必要判断，避免出现这种情况。

        (2)使用负数长度申请内存，负数会被当成一个很大的无符号整数，导致申请内存过大而出现失败。

       3.申请内存后检查是否申请成功，即检查返回指针是否为NULL,即是否为0。

二、内存释放 

        1.申请的内存一定需要释放，有且仅能释放一次

        2.禁止释放或函数内返回非动态申请的内存(栈中的内存，函数中的临时变量等)

　　 3.指针释放后必须将指针指向空指针，否则会出现野指针的情况。

三、附加一个C实现的存储二叉树元素的动态栈

#include<stdio.h>
#include<string.h>
#include<malloc.h>
#define LH_MALLOC(pMemory,Type,Size)  
        if(Size > 0)
        {
            pMemory=(Type*)calloc(Size/sizeof(Type),sizeof(Type));
        }
        else
        {
            pMemory=NULL;
        }

#define LH_FREE(p)  if(NULL != p){free(p);p=NULL;}

#define LH_MEMORY_MOV(dst,dstSize,src,srcSize,Type)
           LH_MALLOC(dst,Type,dstSize)
           memcpy(dst,src,srcSize);
    　　    LH_FREE(src)

typedef struct tagTreeNode
{
    int v;
    struct tagTreeNode* pleft;
    struct tagTreeNode* pright;
}TreeNode;

typedef struct tagLinearStack
{
   TreeNode* ptrees;
   int* ptags;
   int maxsize;
   int index;
}LinearStack;

/*获取一个栈指针*/
LinearStack* getALinearStack()
{
    LinearStack* pstack;
    LH_MALLOC(pstack,LinearStack,sizeof(LinearStack));
    return pstack;
}

/*释放栈，与getALinearStack成对使用*/
void freeLinearStack(LinearStack* pstack)
{
    LH_FREE(pstack->ptags);
    LH_FREE(pstack->ptrees);
    LH_FREE(pstack);
}

/*入栈*/
void push(LinearStack* pstack,TreeNode node)
{
    if(pstack->ptrees == 0 && pstack->ptags == 0)
    {
        LH_MALLOC(pstack->ptrees,TreeNode,sizeof(TreeNode)*5);
        LH_MALLOC(pstack->ptags,int,sizeof(int)*5);
        pstack->maxsize=5;
    }

    if(pstack->index < pstack->maxsize)
    {
       pstack->ptrees[pstack->index++]=node;
    }
    else
    {
       TreeNode* tmpTrees;
       int* tmptags;
       LH_MEMORY_MOV(tmpTrees,
            　　     sizeof(TreeNode)*pstack->maxsize*2,
             　　　　pstack->ptrees,
                    sizeof(TreeNode)*pstack->maxsize,
                    TreeNode);

       LH_MEMORY_MOV(tmptags,
             　　    sizeof(int)*pstack->maxsize*2,
             　　　　 pstack->ptags,
             　　　　 sizeof(int)*pstack->maxsize,
             　　　　 int);
       pstack->ptrees=tmpTrees;
       pstack->ptags=tmptags;
       pstack->maxsize=pstack->maxsize*2;
       pstack->ptrees[pstack->index++]=node;
    }
}

/*弹出栈*/
TreeNode pop(LinearStack* pstack)
{
    if(pstack->index > 0)
    {
       return pstack->ptrees[--pstack->index];
    }
}

void main()
{
    LinearStack* pstack=getALinearStack();
    if(NULL == pstack) 
       retrun;
    for(int i=0;i<60000;i++)
    {
        a.v=i;
        push(pstack,a);
    }
    for(int j=0;j<60000;j++)
    {
    TreeNode node=pop(pstack);
        printf("%d: %d 
",j,node.v);
    }
    freeLinearStack(pstack);
}

四、二叉树非递归遍历方法

void preOrder(TreeNode* pnode)
{
  LinearStack* pstack=getALinearStack();
  while(NULL != pnode || pstack->index > 0)
  {
      while(NULL!=pnode)
      {
          printf("%c ",pnode->v);
          push(pstack,*pnode);
          pnode=pnode->pleft;
      }
      pnode=pop(pstack);
      pnode=pnode->pright;
  }
  freeLinearStack(pstack);
}

void middleOrder(TreeNode* pnode)
{
 LinearStack* pstack=getALinearStack();
 while(NULL != pnode || pstack->index > 0)
 {
     while(NULL!=pnode)
     {
         push(pstack,*pnode);
         pnode=pnode->pleft;
     }
     pnode=pop(pstack);
     printf("%c ",pnode->v);
     pnode=pnode->pright;
 }
 freeLinearStack(pstack);
}

void postOrder(TreeNode* pnode)
{
 LinearStack* pstack=getALinearStack();
 while(NULL != pnode || pstack->index > 0)
 {
     while(NULL != pnode)
     {
        push(pstack,*pnode);
        pstack->ptags[pstack->index-1]=0;
        pnode=pnode->pleft;
     }
     if(pstack->ptags[pstack->index-1]==0)
     {
        pstack->ptags[pstack->index-1]=1;
        pnode=pstack->ptrees[pstack->index-1].pright;
     }
     else
     {
         while(pstack->ptags[pstack->index-1]==1)
         {
             pnode=pop(pstack);
             printf("%c ",pnode->v);
         }
         pnode=NULL;
     }
 }
 freeLinearStack(pstack);
}

void init()
{
    a.v='a';a.pleft=&b;a.pright=&c;
    b.v='b';b.pleft=&d;b.pright=&e;
    c.v='c';c.pleft=0;c.pright=0;
    d.v='d';d.pleft=0;d.pright=&f;
    e.v='e';e.pleft=&g;e.pright=0;
    f.v='f';f.pleft=0;f.pright=0;
    g.v='g';g.pleft=0;g.pright=0;
}


void main()
{
    init();
    postOrder(&a);
}

 五、线索二叉树

typedef enum{Link,Thread} PointerTag;

typedef struct tagTreeNode
{
    char v;
    PointerTag ltag,rtag;
    struct tagTreeNode* pleft;
    struct tagTreeNode* pright;
}TreeNode;
TreeNode a,b,c,d,e,f,g;
void init()
{
    a.v='a';a.pleft=&b;a.pright=&c;
    b.v='b';b.pleft=&d;b.pright=&e;
    c.v='c';c.pleft=0;c.pright=0;
    d.v='d';d.pleft=0;d.pright=&f;
    e.v='e';e.pleft=&g;e.pright=0;
    f.v='f';f.pleft=0;f.pright=0;
    g.v='g';g.pleft=0;g.pright=0;
}
TreeNode *pre;
void InitThreadRootTree(TreeNode* ptree)
{
    if(NULL != ptree)
    {
        InitThreadRootTree(ptree->pleft);
         
        if(ptree->pleft == NULL)
        {
            ptree->ltag=Thread;
            ptree->pleft=pre;
        }
        if(pre->pright == NULL)
        {
            pre->rtag=Thread;
            pre->pright=ptree;
        }
        pre=ptree;

        InitThreadRootTree(ptree->pright);
    }
}
void BuildThread(TreeNode* phead,TreeNode* ptreeRoot)
{
    if(NULL == ptreeRoot)
    {
        phead->ltag=Link;
        phead->pleft=phead;
    }
    else
    {
        
        phead->ltag=Link;
        phead->pleft=ptreeRoot;
        pre=phead;

        InitThreadRootTree(ptreeRoot);

        pre->pright=phead;
        pre->rtag=Thread;
        phead->pright=pre;
    }
}

void midOrderThread(TreeNode* phead)
{
    TreeNode* treeNode = phead->pleft;
    while(phead != treeNode)
    {
          while(treeNode->ltag == Link)
          {
            treeNode=treeNode->pleft;
          }
          printf("%c ",treeNode->v);
          while(treeNode->rtag==Thread && treeNode->pright != phead)
          {
              treeNode=treeNode->pright;
               printf("%c ",treeNode->v);
          }
          treeNode=treeNode->pright;
    }
}

void main()
{
    init();
    TreeNode head;
    head.rtag=Link;
    head.pright=&head;
    BuildThread(&head,&a);
    midOrderThread(&head);
}