实验五：用callback增强链表模块来实现命令行菜单小程序V2.8

【孙剑峰 SA16225264 + 《软件工程（C编码实践篇）》MOOC课程作业http://mooc.study.163.com/course/USTC-1000002006】

代码地址： http://git.shiyanlou.com/csxiaoyao/shiyanlou_cs122/src/master

1. 实验要求

（本实验在提供的代码基础上进行）

1. 给lab5-1.tar.gz(在实验楼Linux虚拟机环境下~/se_files/目录下)找bug，quit命令无法运行的bug
2. 利用callback函数参数使Linktable的查询接口更加通用
3. 注意接口的信息隐藏

2. 实验思路

1. 根据实验要求，首先在Code/shiyanlou_cs122目录下新创建lab5文件夹，将提供的代码文件拷贝在该文件夹下
2. 本次实验是lab4的进一步优化，要求利用callback函数参数使Linktable的查询接口更加通用，同样应该有2个.c和一个.h作为接口文件。本实验的.c文件是menu.c和linktable.c，.h文件是linktable.h
3. 详细设计代码。menu.c文件主要完成静态数组的初始化和命令行菜单功能函数的实现；linklist.c文件主要实现链表的创建、增加、删除等操作；linklist.h文件主要是数据结构的定义和链表操作方法的声明；输入需要保证界面友好

3. 实验过程

1. 在se_files/目录下解压文件lab5-1.tar.gz，生成lab5.1文件夹，里面包含linktable.h、menu.c等文件，将这四个文件复制到Code/shiyanlou_cs122/lab5/目录下。

$ tar -zxvf ./se_files/lab5.1/lab5-1.tar.gz
$ cp ./se_files/lab5.1/* ./Code/shiyanlou_cs122/lab5

2. 查找quit命令无法运行的bug：经过通读程序，发现在SearchLinkTableNode方法的while循环中尾指针指向的结点没有参与循环，修改while循环条件

   

3. 利用callback函数参数使Linktable的查询接口更加通用

   menu.c

#include <stdio.h>
#include <stdlib.h>
#include "linktable.h"
int Help();
int Quit();
#define CMD_MAX_LEN 128
#define DESC_LEN    1024
#define CMD_NUM     10
/* data struct and its operations */
typedef struct DataNode
{
    tLinkTableNode * pNext;
    char*   cmd;
    char*   desc;
    int     (*handler)();
} tDataNode;
int SearchCondition(tLinkTableNode * pLinkTableNode, void * args)
{
    char* cmd =(char*)args;
    tDataNode * pNode = (tDataNode *)pLinkTableNode;
    if(strcmp(pNode->cmd, cmd) == 0)
    {
        return  SUCCESS;
    }
    return FAILURE;
}
/* find a cmd in the linklist and return the datanode pointer */
tDataNode* FindCmd(tLinkTable * head, char * cmd)
{
    return  (tDataNode*)SearchLinkTableNode(head,SearchCondition,cmd);
}
/* show all cmd in listlist */
int ShowAllCmd(tLinkTable * head)
{
    tDataNode * pNode = (tDataNode*)GetLinkTableHead(head);
    while(pNode != NULL)
    {
        printf("%s - %s\n", pNode->cmd, pNode->desc);
        pNode = (tDataNode*)GetNextLinkTableNode(head,(tLinkTableNode *)pNode);
    }
    return 0;
}
int InitMenuData(tLinkTable ** ppLinktable)
{
    *ppLinktable = CreateLinkTable();
    tDataNode* pNode = (tDataNode*)malloc(sizeof(tDataNode));
    pNode->cmd = "help";
    pNode->desc = "Menu List:";
    pNode->handler = Help;
    AddLinkTableNode(*ppLinktable,(tLinkTableNode *)pNode);
    pNode = (tDataNode*)malloc(sizeof(tDataNode));
    pNode->cmd = "version";
    pNode->desc = "Menu Program V1.0";
    pNode->handler = NULL;
    AddLinkTableNode(*ppLinktable,(tLinkTableNode *)pNode);
    pNode = (tDataNode*)malloc(sizeof(tDataNode));
    pNode->cmd = "quit";
    pNode->desc = "Quit from Menu Program V1.0";
    pNode->handler = Quit;
    AddLinkTableNode(*ppLinktable,(tLinkTableNode *)pNode);
    return 0;
}
/* menu program */
tLinkTable * head = NULL;
int main()
{
    InitMenuData(&head);
    /* cmd line begins */
    char cmd[CMD_MAX_LEN];
    while(1)
    {
        printf("Input a cmd number > ");
        scanf("%s", cmd);
        tDataNode *p = FindCmd(head, cmd);
        if( p == NULL)
        {
            printf("This is a wrong cmd!\n ");
            continue;
        }
        printf("%s - %s\n", p->cmd, p->desc);
        if(p->handler != NULL)
        {
            p->handler();
        }
    }
}
int Help()
{
    ShowAllCmd(head);
    return 0;
}
int Quit()
{
    exit(0);
}

linktable.h

#ifndef _LINK_TABLE_H_
#define _LINK_TABLE_H_
#include <pthread.h>
#define SUCCESS 0
#define FAILURE (-1)
/*
 * LinkTable Node Type
 */
typedef struct LinkTableNode
{
    struct LinkTableNode *pNext;
}tLinkTableNode;
/*
 * LinkTable Type
 */
typedef struct LinkTable tLinkTable;
/*
 * Create a LinkTable
 */
tLinkTable * CreateLinkTable();
/*
 * Delete a LinkTable
 */
int DeleteLinkTable(tLinkTable *pLinkTable);
/*
 * Add a LinkTableNode to LinkTable
 */
int AddLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode);
/*
 * Delete a LinkTableNode from LinkTable
 */
int DelLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode);
/*
 * Search a LinkTableNode from LinkTable
 * int Conditon(tLinkTableNode * pNode);
 */
tLinkTableNode * SearchLinkTableNode(tLinkTable *pLinkTable, int Conditon(tLinkTableNode * pNode,void * args),void *args);
/*
 * get LinkTableHead
 */
tLinkTableNode * GetLinkTableHead(tLinkTable *pLinkTable);
/*
 * get next LinkTableNode
 */
tLinkTableNode * GetNextLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode);
#endif /* _LINK_TABLE_H_ */

linktable.c

#include<stdio.h>
#include<stdlib.h>
#include"linktable.h"
struct LinkTable
{
    tLinkTableNode *pHead;
    tLinkTableNode *pTail;
    int         SumOfNode;
    pthread_mutex_t mutex;
};
/*
 * Create a LinkTable
 */
tLinkTable * CreateLinkTable()
{
    tLinkTable * pLinkTable = (tLinkTable *)malloc(sizeof(tLinkTable));
    if(pLinkTable == NULL)
    {
        return NULL;
    }
    pLinkTable->pHead = NULL;
    pLinkTable->pTail = NULL;
    pLinkTable->SumOfNode = 0;
    pthread_mutex_init(&(pLinkTable->mutex), NULL);
    return pLinkTable;
}
/*
 * Delete a LinkTable
 */
int DeleteLinkTable(tLinkTable *pLinkTable)
{
    if(pLinkTable == NULL)
    {
        return FAILURE;
    }
    while(pLinkTable->pHead != NULL)
    {
        tLinkTableNode * p = pLinkTable->pHead;
        pthread_mutex_lock(&(pLinkTable->mutex));
        pLinkTable->pHead = pLinkTable->pHead->pNext;
        pLinkTable->SumOfNode -= 1 ;
        pthread_mutex_unlock(&(pLinkTable->mutex));
        free(p);
    }
    pLinkTable->pHead = NULL;
    pLinkTable->pTail = NULL;
    pLinkTable->SumOfNode = 0;
    pthread_mutex_destroy(&(pLinkTable->mutex));
    free(pLinkTable);
    return SUCCESS;
}
/*
 * Add a LinkTableNode to LinkTable
 */
int AddLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode)
{
    if(pLinkTable == NULL || pNode == NULL)
    {
        return FAILURE;
    }
    pNode->pNext = NULL;
    pthread_mutex_lock(&(pLinkTable->mutex));
    if(pLinkTable->pHead == NULL)
    {
        pLinkTable->pHead = pNode;
    }
    if(pLinkTable->pTail == NULL)
    {
        pLinkTable->pTail = pNode;
    }
    else
    {
        pLinkTable->pTail->pNext = pNode;
        pLinkTable->pTail = pNode;
    }
    pLinkTable->SumOfNode += 1 ;
    pthread_mutex_unlock(&(pLinkTable->mutex));
    return SUCCESS;
}
/*
 * Delete a LinkTableNode from LinkTable
 */
int DelLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode)
{
    if(pLinkTable == NULL || pNode == NULL)
    {
        return FAILURE;
    }
    pthread_mutex_lock(&(pLinkTable->mutex));
    if(pLinkTable->pHead == pNode)
    {
        pLinkTable->pHead = pLinkTable->pHead->pNext;
        pLinkTable->SumOfNode -= 1 ;
        if(pLinkTable->SumOfNode == 0)
        {
            pLinkTable->pTail = NULL;
        }
        pthread_mutex_unlock(&(pLinkTable->mutex));
        return SUCCESS;
    }
    tLinkTableNode * pTempNode = pLinkTable->pHead;
    while(pTempNode != NULL)
    {
        if(pTempNode->pNext == pNode)
        {
            pTempNode->pNext = pTempNode->pNext->pNext;
            pLinkTable->SumOfNode -= 1 ;
            if(pLinkTable->SumOfNode == 0)
            {
                pLinkTable->pTail = NULL;
            }
            pthread_mutex_unlock(&(pLinkTable->mutex));
            return SUCCESS;
        }
        pTempNode = pTempNode->pNext;
    }
    pthread_mutex_unlock(&(pLinkTable->mutex));
    return FAILURE;
}
/*
 * Search a LinkTableNode from LinkTable
 * int Conditon(tLinkTableNode * pNode);
 */
tLinkTableNode * SearchLinkTableNode(tLinkTable *pLinkTable, int Conditon(tLinkTableNode * pNode,void * args), void * args)
{
    if(pLinkTable == NULL || Conditon == NULL)
    {
        return NULL;
    }
    tLinkTableNode * pNode = pLinkTable->pHead;
    while(pNode != NULL)
    {
        if(Conditon(pNode,args) == SUCCESS)
        {
            return pNode;
        }
        pNode = pNode->pNext;
    }
    return NULL;
}
/*
 * get LinkTableHead
 */
tLinkTableNode * GetLinkTableHead(tLinkTable *pLinkTable)
{
    if(pLinkTable == NULL)
    {
        return NULL;
    }
    return pLinkTable->pHead;
}
/*
 * get next LinkTableNode
 */
tLinkTableNode * GetNextLinkTableNode(tLinkTable *pLinkTable,tLinkTableNode * pNode)
{
    if(pLinkTable == NULL || pNode == NULL)
    {
        return NULL;
    }
    tLinkTableNode * pTempNode = pLinkTable->pHead;
    while(pTempNode != NULL)
    {
        if(pTempNode == pNode)
        {
            return pTempNode->pNext;
        }
        pTempNode = pTempNode->pNext;
    }
    return NULL;
}

4. 运行结果

5. 实验总结

通过这实验，我明白了什么是Callback机制。如果把函数的指针（地址）作为参数传递给另一个函数，当这个指针被用为调用它所指向的函数时，我们就说这是回调函数。回调函数不是由该函数的实现方直接调用，而是在特定的事件或条件发生时由另外的一方调用的，用于对该事件或条件进行响应。