C语言复习（一）文件操作

C语言—文件操作

1.1 fgets() + fputs()： 以字符串形式存取数据定义文件指针

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
using namespace std;

/*
文件结束标志: EOF --- feof()

读写文件:
fgetc: file get char 以字符形式获取
fputc: file put char 以字符形式写到文件

*/
int main()
{
    //定义文件指针
    FILE *fp;
    //打开文件
    fp = fopen("fopen_01.txt", "w+");

    //判断文件打开是否成功
    if (!fp) {
        printf("打开文件失败\n");
        exit(0);
    }

    //写的方式: 自己移动
    fputc('a', fp);
    fputc('b', fp);
    fputc('c', fp);

    //打开文件
    fclose(fp);


    //只读文件
    FILE *read = fopen("fopen_01.txt", "r");

    if (!read) {
        printf("打开文件失败\n");
        exit(0);
    }

    //读文件
    //fgetc(): 放回int值, 以字符形式获取
    int ch = fgetc(read);
    while (ch != EOF)
    {
        putchar(ch);        //打印字符到命令行
        ch = fgetc(read);
    }

    printf("\n");

    fclose(read);

    return 0;

}

2.2 fgets() + fputs()： 以字符串形式存取数据

#define _CRT_SECURE_NO_WARNINGS
#include <cstdlib>
#include <cstdio>
using namespace std;

/*

int fputs(char *str, FILE *fp);
char* fgets(char *str, int n, FILE *fp);

*/
int main()
{
    FILE *fp = fopen("fgets_fputs_02.txt", "w+");

    if (!fp) {
        printf("打开文件失败");
        exit(1);
    }

    //写的方式: 自己移动
    int isok = fputs("Douzi is cute\n I love china!\n who are you?", fp);
    //返回非负值，表示成功
    printf("返回非负值表示成功: %d\n", isok);
    
    fclose(fp);

    FILE *read = fopen("fgets_fputs_02.txt", "r");
    if (!read) {
        printf("打开文件失败\n");
        exit(1);
    }

    //读文件
    char str[50] = "";
    //设置读取的长度
     while (fgets(str, 50, read))
    {
        puts(str);
    }
    //puts(str);

    fclose(read);

    return 0;

}

2.3 fread() + fwrite(): 以 二进制 形式存取数据

2.3.1 结构体数据

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cstring>
using namespace std;

/*
//以二进制形式存储数据
int fwrite(void *buffer,unsigned size, unsigned count, FILE * fp)

//以什么方式写进去就以什么方式读出 !!
int fread(void *buffer,unsigned size, unsigned count, FILE * fp)
*/

struct student
{
    char name[20];
    int age;
    double num;
}mystudent;

int main()
{
    //写文件
    FILE *fp = fopen("fread_fwrite_03.bat", "wb");
    if (fp == NULL) {
        printf("打开失败\n");
        exit(1);
    }

    while (true)
    {
        printf("输入姓名-年龄-成绩:\n");
        scanf("%s%d%lf", &mystudent.name, &mystudent.age, &mystudent.num);
        //参数: 源起始位置, 写多少(字节), 写的次数, 目的地
        //     &mystudent, sizeof(struct student), 1, fp
        fwrite(&mystudent, sizeof(struct student), 1, fp);
        printf("是否继续?(Y/N)");

        //清除缓冲区
        //否则下面的字符无法输入，因为上面输入按下回车，"回车"会被下面的getchar()吃掉，而无法自己输入
        fflush(stdin);
        int ch = getchar();
        if (ch == 'N' || ch == 'n') {
            break;
        }
    }
    fclose(fp);

    //读取文件
    FILE *read = fopen("fread_fwrite_03.bat", "rb");
    if (!read) {
        printf("文件打开失败\n");
        exit(1);
    }

    //以二进制形式读取
    while (fread(&mystudent, sizeof(struct student), 1, read) > 0) {
        printf("姓名\t年龄\t成绩:\n");
        printf("%s\t%d\t%.2f\n", mystudent.name, mystudent.age, mystudent.num);
    }    

    fclose(read);

    return 0;

}

2.3.2 结构体数组

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cstring>
using namespace std;

/*
//以二进制形式存储数据
int fwrite(void *buffer,unsigned size, unsigned count, FILE * fp)

//以什么方式写进去就以什么方式读出 !!
int fread(void *buffer,unsigned size, unsigned count, FILE * fp)：
    count: 知道有多少数据可以读取

*/

const int maxn = 1024 + 10;
struct student
{
    char name[20];
    int age;
    double num;
}stus[maxn];

int main()
{
    ////写文件
    FILE *fp = fopen("fread_fwrite_03.bat", "wb");
    if (fp == NULL) {
        printf("打开失败\n");
        exit(1);
    }


    int cnt;
    scanf("%d", &cnt);
    for (int i = 0; i < cnt; i++)
    {
        printf("输入姓名-年龄-成绩:\n");
        scanf("%s%d%lf", &stus[i].name, &stus[i].age, &stus[i].num);        
        
        //清除缓冲区
        //否则下面的字符无法输入，因为上面输入按下回车，"回车"会被下面的getchar()吃掉，而无法自己输入
        fflush(stdin);
    }
    //参数: 源起始位置, 写多少(字节), 写的次数, 目的地
    //     stus, sizeof(struct student), cnt, fp
    fwrite(stus, sizeof(struct student), cnt, fp);

    fclose(fp);

    //读取文件
    FILE *read = fopen("fread_fwrite_03.bat", "rb");
    if (!read) {
        printf("文件打开失败\n");
        exit(1);
    }

    student read_demo[maxn];
    fread(read_demo, sizeof(struct student), cnt, read);
    
    for (int i = 0; i < cnt; i++){
        printf("姓名\t年龄\t成绩:\n");
        printf("%s\t%d\t%.2f\n", read_demo[i].name, read_demo[i].age, read_demo[i].num);
    }



    return 0;

}