第11课 · 文件

FILE *fp;          // fp 是指向 FILE 类型数据的指针变量

if ((fp = fopen("file1", "r")) == NULL)
{
    printf("cannot open this file\n");
    exit(0);
}

fprintf(文件指针, 格式字符串, 输出表列);
fscanf(文件指针, 格式字符串, 输入表列);

fread(buffer, size, count, fp);
fwrite(buffer, size, count, fp);

for (i = 0; i < 40; i++)
    fread(&stud[i], sizeof(struct Student_type), 1, fp);   // 读一个学生
for (i = 0; i < 40; i++)
    fwrite(&stud[i], sizeof(struct Student_type), 1, fp);  // 写一个学生

rewind(fp);

fseek(文件类型指针, 位移量, 起始点);

i = ftell(fp);                    // 变量 i 存放文件当前位置
if (i == -1L) printf("error\n");  // 出错则输出 error

fseek(fp, i * sizeof(struct Student_type), 0);   // i 取 0,2,4,6,8

#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *fp;
    char ch, filename[10];
    printf("请输入所用的文件名：");
    scanf("%s", filename);
    getchar();
    if ((fp = fopen(filename, "w")) == NULL)
    {
        printf("cannot open file\n");
        exit(0);
    }
    printf("请输入一个准备存储到磁盘的字符串（以#结束）：");
    ch = getchar();
    while (ch != '#')
    {
        fputc(ch, fp);
        putchar(ch);
        ch = getchar();
    }
    fclose(fp);
    putchar(10);
    return 0;
}

请输入所用的文件名：file1.dat
请输入一个准备存储到磁盘的字符串（以#结束）：computer and c#
computer and c

#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *in, *out;
    char ch, infile[10], outfile[10];
    printf("输入读入文件的名字：");
    scanf("%s", infile);
    printf("输入输出文件的名字：");
    scanf("%s", outfile);
    if ((in = fopen(infile, "r")) == NULL)
    {
        printf("无法打开此文件\n");
        exit(0);
    }
    if ((out = fopen(outfile, "w")) == NULL)
    {
        printf("无法打开此文件\n");
        exit(0);
    }
    ch = fgetc(in);
    while (!feof(in))
    {
        fputc(ch, out);
        putchar(ch);
        ch = fgetc(in);
    }
    putchar(10);
    fclose(in);
    fclose(out);
    return 0;
}

输入读入文件的名字：file1.dat
输入输出文件的名字：file2.dat
computer and c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
    FILE *fp;
    char str[3][10], temp[10];
    int i, j, k, n = 3, len;
    printf("Enter strings:\n");
    for (i = 0; i < n; i++)
    {
        fgets(str[i], 10, stdin);
        len = (int)strlen(str[i]);
        if (len > 0 && str[i][len - 1] == '\n')
            str[i][len - 1] = '\0';
    }
    for (i = 0; i < n - 1; i++)
    {
        k = i;
        for (j = i + 1; j < n; j++)
            if (strcmp(str[k], str[j]) > 0) k = j;
        if (k != i)
        {
            strcpy(temp, str[i]);
            strcpy(str[i], str[k]);
            strcpy(str[k], temp);
        }
    }
    if ((fp = fopen("D:\\CC\\string.dat", "w")) == NULL)
    {
        printf("can't open file!\n");
        exit(0);
    }
    printf("\nThe new sequence:\n");
    for (i = 0; i < n; i++)
    {
        fputs(str[i], fp);
        fputs("\n", fp);
        printf("%s\n", str[i]);
    }
    fclose(fp);
    return 0;
}

Enter strings:
CHINA
CANADA
INDIA

The new sequence:
CANADA
CHINA
INDIA

#include <stdio.h>
#define SIZE 10
struct Student_type
{
    char name[10];
    int num;
    int age;
    char addr[15];
} stud[SIZE];

void save()
{
    FILE *fp;
    int i;
    if ((fp = fopen("stu.dat", "wb")) == NULL)
    {
        printf("cannot open file\n");
        return;
    }
    for (i = 0; i < SIZE; i++)
        if (fwrite(&stud[i], sizeof(struct Student_type), 1, fp) != 1)
            printf("file write error\n");
    fclose(fp);
}

int main()
{
    int i;
    printf("Please enter data of students:\n");
    for (i = 0; i < SIZE; i++)
        scanf("%s%d%d%s", stud[i].name, &stud[i].num, &stud[i].age, stud[i].addr);
    save();
    return 0;
}

Please enter data of students:
Zhang 1001 19 room_101
Sun 1002 20 room_102
...

#include <stdio.h>
int main()
{
    FILE *fp1, *fp2;
    char ch;
    fp1 = fopen("file1.dat", "r");
    fp2 = fopen("file2.dat", "w");
    ch = getc(fp1);
    while (!feof(fp1))
    {
        putchar(ch);
        ch = getc(fp1);
    }
    putchar(10);
    rewind(fp1);
    ch = getc(fp1);
    while (!feof(fp1))
    {
        fputc(ch, fp2);
        ch = fgetc(fp1);
    }
    fclose(fp1);
    fclose(fp2);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
struct Student_type
{
    char name[10];
    int num;
    int age;
    char addr[15];
} stud[10];

int main()
{
    int i;
    FILE *fp;
    if ((fp = fopen("stu.dat", "rb")) == NULL)
    {
        printf("can not open file\n");
        exit(0);
    }
    for (i = 0; i < 10; i += 2)
    {
        fseek(fp, i * sizeof(struct Student_type), 0);
        fread(&stud[i], sizeof(struct Student_type), 1, fp);
        printf("%-10s%4d%4d%-15s\n", stud[i].name, stud[i].num, stud[i].age, stud[i].addr);
    }
    fclose(fp);
    return 0;
}

Zhang      1001  19 room_101
Tan        1003  21 room_103
Li         1006  22 room_105
Zhen       1008  16 room_107
Qin        1012  19 room_109

#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *fp;
    int ch;
    fp = fopen("test", "w");
    if (fp == NULL) { printf("cannot open file\n"); exit(0); }
    printf("请输入字符串，以 ! 结束：\n");
    while ((ch = getchar()) != '!' && ch != EOF)
    {
        if (ch >= 'a' && ch <= 'z')
            ch = ch - 32;
        fputc(ch, fp);
    }
    fclose(fp);
    printf("\n已存入文件 test\n");
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
    FILE *fa, *fb, *fc;
    char a[100] = "", b[100] = "", c[200], t;
    int i, j, n, la, lb;
    fa = fopen("A.txt", "r");
    if (fa == NULL) { printf("cannot open A\n"); exit(0); }
    fb = fopen("B.txt", "r");
    if (fb == NULL) { printf("cannot open B\n"); exit(0); }
    fgets(a, 100, fa);
    fgets(b, 100, fb);
    fclose(fa);
    fclose(fb);
    la = (int)strlen(a);
    if (la > 0 && a[la - 1] == '\n') a[la - 1] = '\0';
    lb = (int)strlen(b);
    if (lb > 0 && b[lb - 1] == '\n') b[lb - 1] = '\0';
    strcpy(c, a);
    strcat(c, b);
    n = (int)strlen(c);
    for (i = 0; i < n - 1; i++)
        for (j = 0; j < n - 1 - i; j++)
            if (c[j] > c[j + 1])
            { t = c[j]; c[j] = c[j + 1]; c[j + 1] = t; }
    fc = fopen("C.txt", "w");
    if (fc == NULL) { printf("cannot open C\n"); exit(0); }
    fputs(c, fc);
    fputs("\n", fc);
    fclose(fc);
    printf("%s\n", c);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define N 5
struct Student
{
    int num;
    char name[20];
    float score[3];
    float avg;
};
int main()
{
    FILE *fp;
    struct Student stu[N];
    int i;
    for (i = 0; i < N; i++)
    {
        scanf("%d %s %f %f %f", &stu[i].num, stu[i].name,
              &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
        stu[i].avg = (stu[i].score[0] + stu[i].score[1] + stu[i].score[2]) / 3.0f;
    }
    fp = fopen("stud", "wb");
    if (fp == NULL) { printf("cannot open stud\n"); exit(0); }
    for (i = 0; i < N; i++)
        fwrite(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    printf("已存入 stud\n");
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define N 5
struct Student
{
    int num;
    char name[20];
    float score[3];
    float avg;
};
int main()
{
    FILE *fp;
    struct Student stu[N], t;
    int i, j;
    fp = fopen("stud", "rb");
    if (fp == NULL) { printf("cannot open stud\n"); exit(0); }
    for (i = 0; i < N; i++)
        fread(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    for (i = 0; i < N - 1; i++)
        for (j = i + 1; j < N; j++)
            if (stu[j].avg > stu[i].avg)
            { t = stu[i]; stu[i] = stu[j]; stu[j] = t; }
    fp = fopen("stu_sort", "wb");
    if (fp == NULL) { printf("cannot open stu_sort\n"); exit(0); }
    for (i = 0; i < N; i++)
        fwrite(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    for (i = 0; i < N; i++)
        printf("%s %.2f\n", stu[i].name, stu[i].avg);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define N 5
struct Student
{
    int num;
    char name[20];
    float score[3];
    float avg;
};
int main()
{
    FILE *fp;
    struct Student stu[N + 1], s;
    int i, pos;
    fp = fopen("stu_sort", "rb");
    if (fp == NULL) { printf("cannot open stu_sort\n"); exit(0); }
    for (i = 0; i < N; i++)
        fread(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    printf("输入新学生：学号 姓名 3门成绩\n");
    scanf("%d %s %f %f %f", &s.num, s.name, &s.score[0], &s.score[1], &s.score[2]);
    s.avg = (s.score[0] + s.score[1] + s.score[2]) / 3.0f;
    pos = N;
    for (i = 0; i < N; i++)
        if (s.avg > stu[i].avg) { pos = i; break; }
    for (i = N; i > pos; i--)
        stu[i] = stu[i - 1];
    stu[pos] = s;
    fp = fopen("stu_sort_new", "wb");
    if (fp == NULL) { printf("cannot open stu_sort_new\n"); exit(0); }
    for (i = 0; i <= N; i++)
        fwrite(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    for (i = 0; i <= N; i++)
        printf("%s %.2f\n", stu[i].name, stu[i].avg);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define N 5
struct Student
{
    int num;
    char name[20];
    float score[3];
    float avg;
};
int main()
{
    FILE *fp;
    struct Student stu[N + 1], s;
    int i, pos;
    fp = fopen("stu_sort", "rb");
    if (fp == NULL) { printf("cannot open stu_sort\n"); exit(0); }
    for (i = 0; i < N; i++)
        fread(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    printf("输入新学生：学号 姓名 3门成绩\n");
    scanf("%d %s %f %f %f", &s.num, s.name, &s.score[0], &s.score[1], &s.score[2]);
    s.avg = (s.score[0] + s.score[1] + s.score[2]) / 3.0f;
    pos = N;
    for (i = 0; i < N; i++)
        if (s.avg > stu[i].avg) { pos = i; break; }
    for (i = N; i > pos; i--)
        stu[i] = stu[i - 1];
    stu[pos] = s;
    fp = fopen("stu_sort", "wb");
    if (fp == NULL) { printf("cannot open stu_sort\n"); exit(0); }
    for (i = 0; i <= N; i++)
        fwrite(&stu[i], sizeof(struct Student), 1, fp);
    fclose(fp);
    printf("已写回 stu_sort\n");
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 5
struct Employee
{
    char name[20];
    int num;
    char sex[4];
    int age;
    char addr[30];
    float wage;
    char health[10];
    char edu[10];
};
struct Salary
{
    char name[20];
    float wage;
};
int main()
{
    FILE *fin, *fout;
    struct Employee e;
    struct Salary s;
    int i;
    fin = fopen("employee", "rb");
    if (fin == NULL) { printf("cannot open employee\n"); exit(0); }
    fout = fopen("salary", "wb");
    if (fout == NULL) { printf("cannot open salary\n"); exit(0); }
    for (i = 0; i < N; i++)
    {
        if (fread(&e, sizeof(struct Employee), 1, fin) != 1) break;
        strcpy(s.name, e.name);
        s.wage = e.wage;
        fwrite(&s, sizeof(struct Salary), 1, fout);
    }
    fclose(fin);
    fclose(fout);
    printf("已生成 salary\n");
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 100
struct Salary
{
    char name[20];
    float wage;
};
int main()
{
    FILE *fp;
    struct Salary s[MAX];
    char target[20];
    int n = 0, i, found = 0;
    fp = fopen("salary", "rb");
    if (fp == NULL) { printf("cannot open salary\n"); exit(0); }
    while (n < MAX && fread(&s[n], sizeof(struct Salary), 1, fp) == 1)
        n++;
    fclose(fp);
    printf("要删除的职工姓名：");
    scanf("%s", target);
    fp = fopen("salary", "wb");
    if (fp == NULL) { printf("cannot open salary\n"); exit(0); }
    for (i = 0; i < n; i++)
    {
        if (strcmp(s[i].name, target) == 0)
        {
            found = 1;
            continue;
        }
        fwrite(&s[i], sizeof(struct Salary), 1, fp);
    }
    fclose(fp);
    if (found) printf("已删除 %s\n", target);
    else printf("没找到 %s\n", target);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *fp;
    char line[256];
    int i;
    fp = fopen("lines.txt", "w");
    if (fp == NULL) { printf("cannot open file\n"); exit(0); }
    printf("输入若干行，直接回车（空行）结束：\n");
    while (fgets(line, 256, stdin) != NULL)
    {
        if (line[0] == '\n') break;
        fputs(line, fp);
    }
    fclose(fp);
    fp = fopen("lines.txt", "r");
    if (fp == NULL) { printf("cannot open file\n"); exit(0); }
    while (fgets(line, 256, fp) != NULL)
    {
        for (i = 0; line[i] != '\0'; i++)
            if (line[i] >= 'a' && line[i] <= 'z')
                line[i] = line[i] - 32;
        printf("%s", line);
    }
    fclose(fp);
    return 0;
}

#include <stdio.h>
int main(void)
{
    FILE *fp;
    int ch, n = 0;
    fp = fopen("q1.txt", "w");
    fputs("12345", fp);
    fclose(fp);
    fp = fopen("q1.txt", "r");
    fseek(fp, 2L, SEEK_SET);
    while ((ch = fgetc(fp)) != EOF)
    {
        putchar(ch);
        n++;
    }
    printf(" %d\n", n);
    fclose(fp);
    return 0;
}

#include <stdio.h>
int main(void)
{
    FILE *fp;
    int a = 66;
    fp = fopen("q2.dat", "wb");
    fwrite(&a, sizeof(int), 1, fp);
    fclose(fp);
    a = 0;
    fp = fopen("q2.dat", "rb");
    fread(&a, sizeof(int), 1, fp);
    fclose(fp);
    printf("%d %c\n", a, a);
    return 0;
}

#include <stdio.h>
int main(void)
{
    FILE *fp;
    long p1, p2;
    fp = fopen("q3.txt", "w");
    fputs("ABCDEF", fp);
    fclose(fp);
    fp = fopen("q3.txt", "r");
    fgetc(fp);
    fgetc(fp);
    p1 = ftell(fp);
    fseek(fp, -3L, SEEK_END);
    p2 = ftell(fp);
    printf("%ld %ld %c\n", p1, p2, fgetc(fp));
    fclose(fp);
    return 0;
}

打开 data.txt（只读）
sum = 0
for i = 1 to 10
    读一个整数 x
    sum = sum + x
关闭文件
输出 sum

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    FILE *fp;
    char s[50];
    fp = fopen("note.txt", "w");
    if (fp == NULL) { printf("cannot open\n"); exit(0); }
    fputs("hello\n", fp);
    /* TODO 1：再把 "world" 写进去，并换行 */
    fclose(fp);
    fp = fopen("note.txt", "r");
    if (fp == NULL) { printf("cannot open\n"); exit(0); }
    /* TODO 2：用 fgets 循环读，读到 NULL 为止，逐个 printf("%s", s) */
    fclose(fp);
    return 0;
}

// ❌ 错误示例（故意）
#include <stdio.h>
int main(void)
{
    FILE *fp;
    int ch;
    fp = fopen("in.txt", "r");
    while ((ch = fgetc(fp)) != EOF)
        putchar(ch);
    fclose(fp);
    return 0;
}

// ❌ 错误示例（故意）
#include <stdio.h>
int main(void)
{
    FILE *fp;
    char ch;
    fp = fopen("in.txt", "r");
    if (fp == NULL) return 1;
    while ((ch = fgetc(fp)) != EOF)
        putchar(ch);
    fclose(fp);
    return 0;
}

// ❌ 错误示例（故意）
#include <stdio.h>
int main(void)
{
    FILE *fp;
    fp = fopen("D:\data\a.txt", "r");
    if (fp == NULL) { printf("cannot open\n"); return 1; }
    fclose(fp);
    return 0;
}