文件编程--实例讲解文件读取和写入

主要通过通讯录链表的存取讲解文件编程

FILE *fopen(const char *path, const char *mode);

const char *path  文件路径

const char *mode 打开方式或者说以什么权限打开

读写之前先打开文件，这里的雷区是读取的格式要严格的与写入保持一致，否则极其容易出错
 

fscanf(file,"%s%s",newnode->num,newnode->name);

fprintf(file2,"%-11s %-15s\r\n",head->next->num,head->next->name);

主要的读取与写入代码单独拿出来一观

我这里是用while循环将读取到的信息以节点的形式放入链表

补充一下：

不带缓存的I/O:       read,write,open......
标准(带缓存的)I/O: fgets,fread,fwrite.....

如果我们直接用非缓存I/O对内核的缓冲区进行读写，会产生许多管理不善而造成的麻烦（如一次性写入过多，或多次系统调用导致的效率低下）。

标准(带缓存的)I/O为我们解决了这些问题，它处理很多细节，如缓冲区分配，以优化长度执行I/O等，更便于我们使用。

具体参考：不带缓冲IO和带缓冲IO - 从菜鸟到菜菜鸟 - CSDN博客  https://blog.csdn.net/carolzhang8406/article/details/7227761

int fscanf_file(Linker *head)
{
    int flag;
    Linker *newnode,*p;
    p = head;
    
    FILE *file = fopen("./addressbook.txt","r");
    if(NULL == file)
    {
        perror("fopen file");
        return F;
    }
    
    fscanf(file,"%d",&flag);
    
    while(flag != 0)                                     //用尾插的方式放入读取的数据
    {
        p = head;
        
        newnode = (Linker *)malloc(sizeof(struct link)); //申请节点把读取的信息逐条放入
        if (newnode == NULL)
        {
            return F;
        }

        while(p->next != NULL)
        {
            p=p->next;
        }

        fscanf(file,"%s%s",newnode->num,newnode->name);
        fscanf(file,"%d",&flag);                          //读取每条信息编号

        newnode->next = NULL;
        p->next = newnode;

    }

    fclose(file);
    return T;
}

int fprint_file(Linker *head)
{
    
    int k = 1;
    FILE *file2 = fopen("./addressbook.txt","w+");//每次重新写入信息
    {
        if(file2 == NULL)
        {
            perror("fopen file2");
            exit(2);
        }
    }

    while(head->next != NULL)
    {
        fprintf(file2, "%d ",k++);   //为联系人编号
        fprintf(file2,"%-11s %-15s\r\n"
                ,head->next->num,head->next->name);
        head = head->next;
    }

    fprintf(file2, "%d\n",0);//标志位，如果只有0，没有联系人
    fclose(file2);

    return T;
}

下面是极简易的通讯录，辅助理解使用 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define T 1
#define F 0

typedef struct link
{
    char num[15];        //学号
    char name[30];       //姓名
    struct link *next;
}Linker;

int fscanf_file(Linker *head);  //从文件夹读取信息
int fprint_file(Linker *head);  //把信息打印到文件

int insert_tail(Linker *head);  //插入联系人
int init(Linker **head);        //初始化
void print(Linker *head);       //显示

int main()
{
	Linker *head;
	init(&head);
	fscanf_file(head);
	insert_tail(head);
	fprint_file(head);
	print(head);
	
	
	return 0;
}

int init(Linker **head)
{
    Linker *newnode = (Linker *)malloc(sizeof(struct link));
    if (newnode == NULL)
    {
        return F;
    }

    newnode->next = NULL;
    *head = newnode;

    return T;
}

void print(Linker *head)
{
    int i = 0;
    if (head->next == NULL)
    {
        printf("无联系人信息！\n");
    }
    else
    {
        printf("\n\n");
        printf("联系人信息：\n\n");
        while(head->next != NULL)
        {
            printf("学号：%-11s 姓名:%-15s\n"
                ,head->next->num,head->next->name);
            head = head->next;
            i++;
        }
        printf("\n共有%d人\n",i);
    }
}

int insert_tail(Linker *head)
{
    Linker *p = head;
    Linker *q = head;
    int i;
    
    Linker *newnode = (Linker *)malloc(sizeof(struct link));
    if (newnode == NULL)
    {
        return F;
    }

    while(p->next != NULL)
    {
        p = p->next;
    }

    printf("\n请输入新建联系人的学号：\n");
    scanf("%s",newnode->num);
    while(strlen(newnode->num) != 11)
    {
        printf("请重新输入新建联系人的学号：\n");
        scanf("%s",newnode->num);
    }


    printf("\n请输入新建联系人的姓名：\n");
    scanf("%s",newnode->name);
    
    newnode->next = NULL;
    p->next = newnode;
    
    printf("\n*****************添加联系人成功！********************\n");
    
    return T;
}

int fscanf_file(Linker *head)
{
    int flag;
    Linker *newnode,*p;
    p = head;
    
    FILE *file = fopen("./addressbook.txt","r");
    if(NULL == file)
    {
        perror("fopen file");
        return F;
    }
    
    fscanf(file,"%d",&flag);
    
    while(flag != 0)
    {
        p = head;
        
        newnode = (Linker *)malloc(sizeof(struct link));
        if (newnode == NULL)
        {
            return F;
        }

        while(p->next != NULL)
        {
            p=p->next;
        }

        fscanf(file,"%s%s",newnode->num,newnode->name);
        fscanf(file,"%d",&flag);

        newnode->next = NULL;
        p->next = newnode;

    }

    fclose(file);
    return T;
}

int fprint_file(Linker *head)
{
    
    int k = 1;
    FILE *file2 = fopen("./addressbook.txt","w+");//每次重新写入信息
    {
        if(file2 == NULL)
        {
            perror("fopen file2");
            exit(2);
        }
    }

    while(head->next != NULL)
    {
        fprintf(file2, "%d ",k++);   //为联系人编号
        fprintf(file2,"%-11s %-15s\r\n"
                ,head->next->num,head->next->name);
        head = head->next;
    }

    fprintf(file2, "%d\n",0);//标志位，如果只有0，没有联系人
    fclose(file2);

    return T;
}