malloc和calloc的区别

malloc和calloc的区别

昨日写数据结构，写到树的遍历的时候卡了壳.看了几遍源码也没弄明白为何不对.最后发现是malloc和calloc的区别没弄明白导致的.
以下是遍历树前进行的准备.

//
// Created by shangkejie on 2020/4/13.
//
#ifndef LEARNTREE_MYTREE_H
#define LEARNTREE_MYTREE_H
#include 
#include 
#include 
typedef char binTreeElemType;
typedef struct binTree{
    binTreeElemType data;//数据
    struct binTree *lchild;//当前节点的左孩子
    struct binTree *rchild;//当前节点的右孩子
}binTree,*BinTree;
typedef struct tag{
    BinTree p;
    struct tag *next;
}tag,*ptag;
//栈的数据结构
#define MaxSize 50
typedef BinTree ElemType;
typedef struct {
    ElemType data[MaxSize];
    int top;
}myStack;
void initStack(myStack *stack);
bool stackEmpty(myStack *stack);
bool stackPush(myStack *stack,ElemType x);
bool stackPop(myStack *stack,ElemType *x);
bool stackGetTop(myStack *stack,ElemType *x);
//队列相关数据结构
typedef struct linkNode{
    ElemType data;
    struct linkNode *linkNext;
}linkNode;
typedef struct {
    linkNode *front,*rear;
}linkQueue;
void initQueue(linkQueue *linkQueue);
bool queueEmpty(linkQueue linkQueue);
void enQueue(linkQueue *linkQueue,ElemType x);
bool delQueue(linkQueue *linkQueue,ElemType *x);
#endif //LEARNTREE_MYTREE_H

分析一下源码

#include "myTree.h"

void PrePrint(BinTree pTree);

int main() {
    BinTree treeNew;
    int i,j,pos;
    char ch;
    BinTree tree=NULL;//树根
    ptag pHead=NULL,pTail=NULL,listPNew,pCur;
    //abcdefghij
    while (scanf("%c",&ch)!=EOF){
        if (ch=='\n'){
            break;
        }
        treeNew=(BinTree)malloc(sizeof(struct binTree));
        treeNew->data=ch;
        listPNew=(ptag)malloc(sizeof(struct tag));
        listPNew->p=treeNew;
        if (NULL==tree){
            tree=treeNew;
            pHead=listPNew;
            pTail=listPNew;
            pCur=listPNew;
            continue;
        } else{
            pTail->next=listPNew;
            pTail=listPNew;
        }
        if (NULL==pCur->p->lchild){//左子树为空
            pCur->p->lchild=treeNew;
        } else if (NULL==pCur->p->rchild){//右子树为空
            pCur->p->rchild=treeNew;
            pCur=pCur->next;
        }
    }
    printf("--------PreOrder--------\n");
    PrePrint(tree);
    printf("\n--------INOrder--------\n");
    printf("\n--------POSTOrder--------\n");
    printf("\n--------PreOrder--------\n");
    return 0;
}

void PrePrint(BinTree pTree) {
    if (pTree!=NULL){
        printf("%c",pTree->data);
        //putchar(pTree->data);
        PrePrint(pTree->lchild);
        PrePrint(pTree->rchild);
    }
}

记过Debug,发现了错误原因,此处直接跳过了.

 if (NULL==pCur->p->lchild){//左子树为空
            pCur->p->lchild=treeNew;
          

为什么会跳过呢?不应该是NULL吗?
百思不得姐,然后又一字不差的对了一遍源码?发现是malloc的原因.

malloc初始化的空间是带有数据的,只不过数据的随机的.称之为"脏数据"

将malloc改为calloc以后.,问题迎刃而解.

  treeNew=(BinTree)calloc(1,sizeof(struct binTree));
        treeNew->data=ch;
        listPNew=(ptag)calloc(1,sizeof(struct tag));
        listPNew->p=treeNew;

calloc在初始数据的时候,会将空间初始为默认值,假如是int型的数据,就初始化为0,假如是指针就初始化为NULL

如此以来,便知道了malloc和calloc的不同.

总结

malloc初始化的空间是带有数据的,只不过数据的随机的.称之为"脏数据"

calloc在初始数据的时候,会将空间初始为默认值,假如是int型的数据,就初始化为0,假如是指针就初始化为NULL