C/C++(文件操作二)

二进制读写才是本质

二进制的读写对文件标记不敏感。

eg: 对图片进行加密与解密：

用命令的形式去执行：

//xx.exe -c src dest 加密

//xx.exe -d src dest 解密

他的参数就是argv[0-3]------使用Qt

#include<stdio.h>

#include<stdlib.h>

#include<string.h>

void encode(char *buf,int n) {

    for(int i = 0;i < n;i++) {

        buf[i]++;

    }

}

void decode(char *buf,int n) {

    for(int i = 0;i < n;i++) {

        buf[i]--;

    }

}

int main(int argv,char *argv[]) {

    if(argv != 4) {

        printf("use xx.exe -d[-c] src dest\n");

        exit(-1);

    }

    FILE *pfr = fopen(argv[2],"rb+");

    if(pfr == NULL) {

        exit(-1);

    }

    FILE *pfw = fopen(argv[3],"wb+");

    if(pfw == NULL) {

        fclose(pfr);

        exit(-1);

    }

    int buf[1024];

    int n;

    if(strcmp(argv[1],"-c") == 0) {

        while((n = fread((void *)buf,1,1024,pfr)) > 0) {

            encode(buf,n);//加密函数

            fwrite((void *)buf,1,n,pfw);

        }

    }else if(strcmpy(argc[1],"-d") == 0) {

         while((n = fread((void *)buf,1,1024,pfr)) > 0) {

            encode(buf,n);//加密函数

            fwrite((void *)buf,1,n,pfw);

        }

    }else{

        printf("arg error\n");

    }

    fclose(pfr);

    fclose(pfw);

    return 0;

}

读写结构体的优势

结构体中的数据类型不统一，此时最适合用二进制的方式进行读写。二进制的接口可以读文本，而文本的接口不可以读二进制。

#include<stdio.h>

typedef struct student{

    int num;

    char name[30];

    char sex;

    float math;

    float english;

    float chinese;

}Stu;

int main() {

    Stu s[5] = {

        {1001,"assassin",'f',89,99,100},

        {1002,"wunworld",'f',99,89,79},

        {1003,"intelwisd",'m',98,80,100},

        {1004,"seafwg",'m',99,90,99},

        {1005,"xxxx",'f',90,99,100}

    };//把初始化的内容写进结构体中，读出来。

//把数据以二进制形式保存，文本原样保存

    FILE * pfs = fopen("stu.data","w+");

    if(pfs == NULL) {

        exit(-1);

    }

    for(int i = 0;i < 5;i++) {

        fwrite((void *)&s[i],sizeof(Stu),1,pfs);//注意&s[i],对数组取地址

    }

    fclose(pfs);

    return 0;

}

为什么结构体采用fread/fwrite来都写？

1.结构体数据类型不统一

2.可以将二进制转化为文本，降低效率，占用多余的存储空间。

读文件：

#include<stdio.h>

typedef struct student{

    int num;

    char name[30];

    char sex;

    float math;

    float english;

    float chinese;

}Stu;

int main() {

    Stu s[5] = {

        {1001,"assassin",'f',89,99,100},

        {1002,"wunworld",'f',99,89,79},

        {1003,"intelwisd",'m',98,80,100},

        {1004,"seafwg",'m',99,90,99},

        {1005,"xxxx",'f',90,99,100}

    };//把初始化的内容写进结构体中，读出来。

//把数据以二进制形式保存，文本原样保存

    FILE * pfw = fopen("stu.data","w+");

    if(pfw == NULL) {

        exit(-1);

    }

    Stu s;

    while(fread((void *)&s,sizeof(Stu),1,pfw)) {

        printf("num     = %d\n",s.num);

        printf("name    = %s\n",s.name);

        printf("sex     = %c\n",s.sex);

        printf("math    = %.2f\n",s.math);

        printf("english = %.2f\n",s.english);

        printf("chinese = %.2f\n",s.chinese);

    }

    fclose(pfw);

    return 0;

}

假如以小空间来读大数据的情况,在while循环中使用循环，通过循环的小标逐渐读出数据

#include<stdio.h>

typedef struct student{

    int num;

    char name[30];

    char sex;

    float math;

    float english;

    float chinese;

}Stu;

int main() {

    Stu s[5] = {

        {1001,"assassin",'f',89,99,100},

        {1002,"wunworld",'f',99,89,79},

        {1003,"intelwisd",'m',98,80,100},

        {1004,"seafwg",'m',99,90,99},

        {1005,"xxxx",'f',90,99,100}

    };//把初始化的内容写进结构体中，读出来。

//把数据以二进制形式保存，文本原样保存

    FILE * pfw = fopen("stu.data","w+");

    if(pfw == NULL) {

        exit(-1);

    }

    Stu s[3];//有3个，结构体有5个

    while(fread((void *)&s,sizeof(Stu),1,pfw)) {

        for(int i = 0;i < n;i++) {

            printf("num     = %d\n",s[i].num);

            printf("name    = %s\n",s[i].name);

            printf("sex     = %c\n",s[i].sex);

            printf("math    = %.2f\n",s[i].math);

            printf("english = %.2f\n",s[i].english);

            printf("chinese = %.2f\n",s[i].chinese);

        }

    }

    fclose(pfw);

    return 0;

}

实践：将链表作为内存数据模型，见文件作为数据库，将终端作为交互界面。读文件生成链表，修改链表写入文件。

//1.初始化数据库，此时的数据库是文件

//2.都数据库，生成内存数据模型,链表

//3.增，查，改，删，排序

//4.更新数据库

typedef struct student

{

    char name[30];

    char sex;

    int age;

    float score;

}Stu;

typedef struct _StuNode

{

    Stu data;

    struct _StuNode *next;

}StuNode;

void initData2File()

{

    Stu s[4] =

    {

        {"assassin",'f',30,100},

        {"wunworld",'f',27,79},

        {"intelwisd",'m',25,100},

        {"seafwg",'m',23,99},

        {"xxxx",'f',23,100}

    }

    FILE *pf = fopen("stu.data","w+");

    if(NULL == pf)

        exit(-1);

    fwrite((void *)s,sizeof(s),1,pf);

    fclose(pf);

    return ;

}    

StuNode *createListFromFile(char *filePath)

{

    FILE *pf = fopen(filePath,"r+");//格式写正确不然一不小心会覆盖

    if(NULL == pf)

        exit(-1);

    StuNode *head = (StuNode *)malloc(sizeof(StuNode));

    head->next = NULL;

    StuNode *cur = (StuNode *)malloc(sizeof(StuNode));

    while(fread((void *)&cur->data,sizeof(Stu),1,pf) )

    {

        cur->next = head->next;

        head->next = cur;

        cur = (StuNode *)malloc(sizeof(StuNode));

    }

    free(cur);

    return head;

}

void traverseStuList(StuNode *head)

{

    printf("name\t\t\tsex\t\tage\t\tscore\n");

    head = head->next;

    while(head)

    {

        printf("%-10s\t\t%c\t\t%d\t\t%.2f\n",head->data.name,head->data.sex,head->data.age,head->data.score);

        head = head->next;

    }

}

void addListStuNode(StuNode *head)

{

    StuNode *cur = (StuNode *)malloc(sizeof(StuNode));

    printf("name:\n");

    scanf("%s",cur->data.name);

    getchar();

    printf("sex:\n");

    scanf("%c",&cur->data.sex);

    getchar();

    printf("age:\n");

    scanf("%sd",&cur->data.age);

    getchar();

    printf("score:\n");

    scanf("%f",c&ur->data.score);

    cur->next = head->next;

    head->next = cur;

}

StuNode * searchListStu(StuNode *head)

{

    char name[30];

    printf("pls input your search name:");

    scanf("%d",name);

    head = head->next;

    while(head)

    {

        if(strcmp(head-data.name,name) == 0)

            break;

        head - head->next;

    }

    return head;

}

//删除操作

void deleteListNodeStu(StuNode *head)

{

    StuNode *pfind = searchListStu(head);

    if(pfind == null)

    {

        printf("你所要删除的人不存在！\n");

        return ;

    }

    while(head->next != pfind)

    {

        head = head->next;//找到前驱

    }

    head->next = pfind->next;

    free(pfind);

    return ;

}

//

int lenListStu(StuNode *head)

{

    int len;

    head = head->next;

    while(head)

    {

        len++;

        head = head->next;

    }

    return len;

}

void sortListStu(StuNode *head)

{

    int len = lenListStu(head);

    StuNode *prep,*p,*q;

    for(int i = 0;i < len-1;i++)

    {

        prep = head;

        p = prep->next;

        q = q->next;

        for(int j = 0;j < len-1-i;j++)

        {

        if(strcmp(p->data.name,q->data.name) > 0)

        {

            prep->next = q;

            p->next = q->next;

            q->next = p;

            prep = q;

            q = p->next;

            continue;

        }

        prep = prep->next;

        p = p->next;

        q = q->next;

        }

    }

}

void saveList2FileStu(StuNode *head,char *filePath)

{

    FILE *pf = fopen(filePath,"w+");

    if(NULL == pf)

        exit(-1);

    head = head->next;

    while(head)

    {

        fwrite((void *)&head->data,sizeof(Stu),1,pf);

        head =head->next;

    }

    fclose(pf);

}

void destoryListStu(head)

{

    StuNode *t;//找个替身

    while(head)

    {

        t = head;

        head = head->next;

        free(t);

    }

}

int main()

{

    //initdata2File();

    StuNode *head = createListFromFile("stu.data");

    /*

    traverseStuList(head);

    printf("1->add\t 2->search\t 3->delete\t4->exit\n");

    int choice;

    scanf("%d",&choice);

    switch(choice)

    {

        case 1:

            addListStuNode(head);

            break;

        case 2:

            break;

        case 3:

            break;

        case 4:

            break;

        default:

            printf("你输入错误！\n");

    }*/

    StuNode *pfind;

    while(1)

    {

        system("cls");//系统清屏

        traverseStuList(head);

        printf("1->add\t 2->search\t 3->delete\t4->exit\n");

        int choice;

        scanf("%d",&choice);

        switch(choice)

        {

            case 1:

                addListStuNode(head);

                break;

            case 2:

                if(pfind = searchListStu(head))

                {

                    printf("%-10s\t\t%c\t\t%d\t\t%.2f\n",pfind->data.name,pfind->data.sex,pfind->data.age,pfind->data.score);

                }

                else

                {

                    printf("没有此人！\n");

                }

                break;

            case 3:

                deleteListNodeStu(head);

                break;

            case 4:

                sortListStu(head);

                break;

            case 5:

                saveList2FileStu(head,"stu.data");

                destoryListStu(head);

                return 0;

            default:

                printf("你输入错误！\n");

        }

    }

}

文件偏移

int main()

{

    FILE *pf = fopen("xxx.txt","w=");

    fputs("abcdefg",pf);

    int n = ftell(pf);//

    printf("n = %d\n",n);//n = 7，ftell(),求字节的大小

    rewind(pf);//将文件重新指针向一个流的开头

    n = ftell(pf);

    printf("n = %d\n",n);//0

    feek(pf,0,SEEK_END);//操作文件pf,从SEEK_END末尾偏移0个单位。

    n = ftell(pf);

    printf("n = %d\n",n);//7

    feek(pf,0,SEEK_SET);//从头偏移0个

    n = ftell(pf);

    printf("n = %d\n",n);//0

    feek(pf,1,SEEK_CUR);//从当前位置偏移一个单位

    n = ftell(pf);

    printf("n = %d\n",n);//0

    return 0;

}

巴特西

C/C++(文件操作二)

二进制读写才是本质

读写结构体的优势

读文件：

文件偏移

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