程序通过定义学生结构体变量，存储了学生的学号、姓名和3门课的成绩。所有学生数据均以二进制方式输出到文件中。函数 fun 的功能是重写形参 filename 所指文件中最后一个学生的数据，即用新的学生数据覆盖该学生原来的数据，其他学生的数据不变。按照这个要求修改代码，程序的主体结构不变“”“(char *filename,STU n){ FILE *fp; fp=fopen(filename,"rb"); ​ fseek(fp,1L*sizeof(STU),2); fwrite(n, sizeof(STU), 1, fp); fclose(fp); } void main(){ STU t[N]= {{10001,"MaChao", 91, 92, 77},{10002,"CaoKai",75, 60, 88}, {10003,"LiSi", 85, 70, 78},{10004,"FangFang",90, 82, 87}, {10005,"ZhangSan",95, 80, 88} }; STU n={10006,"ZhaoSi", 55, 70, 68},ss[N]; int i,j; FILE *fp; fp=fopen("student.dat","wb"); fwrite(t, sizeof(STU),N,fp); fclose(fp); fp=fopen("student.dat","rb"); fread(ss, sizeof(STU),N,fp); fclose(fp); printf("\n\nThe original data:\n\n"); for (j=0;j<N;j++) { printf("No: %ld Name:%-8sScores:",ss[j].sno, ss[j].name); for (i=0;i<3;i++) printf("%6.2f", ss[j].score[i]); printf("\n"); } fun("student.dat",n); printf("\n\nThe data after mdifing :\n\n"); fp=fopen("student.dat","rb"); fread(ss, sizeof(STU), N,fp); fclose(fp); for (j=0; j<N; j++) { printf("nNo: %ld Name: %-8s,Scores:",ss[j].sno, ss[j].name); for (i=0; i<3; i++) printf("%6.2f",ss[j].score[i]); printf("\n"); } } ename, "rb")”

修改后的代码如下：

#include <stdio.h>
#define N 5

typedef struct student {
    long sno;
    char name[10];
    float score[3];
} STU;

void fun(char *filename, STU n) {
    FILE *fp;
    fp = fopen(filename, "rb+");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return;
    }
    fseek(fp, -sizeof(STU), SEEK_END);
    fwrite(&n, sizeof(STU), 1, fp);
    fclose(fp);
}

int main() {
    STU t[N] = {
        {10001, "MaChao", {91, 92, 77}},
        {10002, "CaoKai", {75, 60, 88}},
        {10003, "LiSi", {85, 70, 78}},
        {10004, "FangFang", {90, 82, 87}},
        {10005, "ZhangSan", {95, 80, 88}}
    };
    STU n = {10006, "ZhaoSi", {55, 70, 68}}, ss[N];
    int i, j;
    FILE *fp;
    fp = fopen("student.dat", "wb");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return 0;
    }
    fwrite(t, sizeof(STU), N, fp);
    fclose(fp);
    fp = fopen("student.dat", "rb");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return 0;
    }
    fread(ss, sizeof(STU), N, fp);
    fclose(fp);
    printf("\n\nThe original data:\n\n");
    for (j = 0; j < N; j++) {
        printf("No: %ld  Name:%-8sScores:", ss[j].sno, ss[j].name);
        for (i = 0; i < 3; i++)
            printf("%6.2f", ss[j].score[i]);
        printf("\n");
    }
    fun("student.dat", n);
    printf("\n\nThe data after modifying:\n\n");
    fp = fopen("student.dat", "rb");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return 0;
    }
    fread(ss, sizeof(STU), N, fp);
    fclose(fp);
    for (j = 0; j < N; j++) {
        printf("No: %ld  Name:%-8sScores:", ss[j].sno, ss[j].name);
        for (i = 0; i < 3; i++)
            printf("%6.2f", ss[j].score[i]);
        printf("\n");
    }
    return 0;
}

修改的主要内容：

1. 函数 `fun` 中的文件打开模式由 "rb" 修改为 "rb+"，以便进行读写操作。
2. 在函数 `fun` 中，使用 `fseek` 定位到文件结尾前一个学生的位置，再使用 `fwrite` 函数将新的学生数据写入该位置。
3. 在主函数中，输出原始数据时，将 "n" 改为 "No"，并修改输出格式。
4. 在主函数中，修改后的数据输出时，将 "n" 改为 "No"，并修改输出格式。