c - C中的文件I/O写入和读取文件

Question

我是c编程新手。我刚刚开始学习文件i/o。所以我的问题是在我输入写入文件的所有数据后，我的程序说有问题并退出。我的程序的哪一部分错了？

  //THIS PROGRAM WRITE RECORDS IN A TXT.FILE AND THEN READ AND DISPLAY THE RECORDS IN A TXT.FILE

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

struct student
{
    char MatricNo[20];
    int matric[20];
    char CourseNo[20];
    int course[20];
    char Grade[20];
    float Value[20];
 }s[10];

int count=0;

int i,j, no,nu;

int write();
 int read(int i, int j);

int main()
{
int choice;
printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
    printf("Your Choice: ");
    scanf("%i",&choice);
while(choice!=3)
{


    switch(choice)
    {
        case 1:
            write();
            break;
        case 2:
            read(i, j);
            break;
        case 3:
            return 0;
            break;
        default:
            break;
    }
    printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
    printf("Your Choice: ");
    scanf("%i",&choice);
}

fflush(stdin);
getchar();

return 0;
}

// for write data to txt file

int write()
{
    FILE *fw;



   fw=fopen("Register Table.txt","w");



      printf("\nEnter number of student :");
      scanf("%d",&no);

    for(i=0;i<no;i++)
{
    printf("\nEnter student MatricNo :");
    scanf("%s",&s[i].MatricNo);
    printf("\nEnter number of courses :");
    scanf("%d",&nu);
    for(j=0; j < nu; j++)
    {
    printf("\nEnter student CourseNo :");
    scanf("%s",&s[j].CourseNo);
    printf("\nEnter student Grade :");
    scanf("%s",&s[j].Grade);
    printf("\nEnter student value :");
    scanf("%.2f",&s[j].Value);
    fflush(stdin);
fprintf(fw,"%5s %5s %5s %.2f\n",s[i].MatricNo,s[j].CourseNo,s[j].Grade,s[j].Value); 
        fclose(fw); 
   }
   }


   }

int read(int i, int j)
{
FILE *fr;


//read data from txt file
fr=fopen("Register Table.txt","r");

if(!fr){
    printf("not file");
    return 0;
}
else
return 1;

printf("\n\n\t **Register Table  **\n");

    while(fscanf(fr,"%5s %5s %5s %.2f",&s[i].MatricNo,&s[j].CourseNo,&s[j].Grade,&s[j].Value)==1)
    {
            //display data from txt file
printf("\n\n MatricNo\t CourseNo\t Grade\t\t Value");
for(i=0;i<no;i++)
{
    for(j=0; j < nu; j++)
    {
        printf("\n\n %5s %5s %5s %.2f",s[i].MatricNo,s[j].CourseNo,s[j].Grade,s[j].Value);

    }
}

printf("\n\n");
    }

fclose(fr);


}

好的，我编辑了我的程序，就是这样。但是现在的问题是我写入文件后，它无法读取。

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

    struct student
    {
        char MatricNo[20];
        int matric[20];
        char CourseNo[20];
        int course[20];
        char Grade[20];
        float Value[20];
    }s[10];

    int count=0;

    int i,j, no,nu;

    int write();
    int read(int no, int nu);
    FILE *fw;
    int main()
    {
        int choice;
        printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
            printf("Your Choice: ");
            scanf("%i",&choice);
        while(choice!=3)
        {


            switch(choice)
            {
                case 1:
                    write();
                    break;
                case 2:
                    read(no, nu);
                    break;
                case 3:
                    return 0;
                    break;
                default:
                    break;
            }
            printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
            printf("Your Choice: ");
            scanf("%i", &choice);
        }

        fflush(stdin);
        getchar();
        return 0;

    }

    // for write data to txt file

    int write()
    {




        fw=fopen("Register Table.txt","w");



            printf("\nEnter number of student :");
            scanf("%d", &no);

            for(i=0;i<no;i++)
        {
            printf("\nEnter student MatricNo :");
            scanf("%s", &s[i].MatricNo);
            printf("\nEnter number of course :");
            scanf("%d", &nu);
            for(j=0; j < nu; j++)
            {
            printf("\nEnter student CourseNo :");
            scanf("%s", &s[i].CourseNo[j]);
            printf("\nEnter student Grade :");
            scanf("%s", &s[i].Grade[j]);
            printf("\nEnter student value :");
            scanf("%f", &s[i].Value[j]);



        }


        }


                fprintf(fw,"%s %s %s %.2f\n", s[i].MatricNo, s[i].CourseNo[j], s[i].Grade[j], s[i].Value[j]);   

                fclose(fw);

    }

    int read(int no, int nu)
    {
        FILE *fr;


        //read data from txt file
        fr=fopen("Register Table.txt","r");


        printf("\n\n\t **Register Table  **\n");


                for(i=0;i<no;i++)
                    {
                         for(j=0; j < nu; j++)
                            {
                                fscanf(fr,"%s %s %s %.2f", &s[i].MatricNo, &s[i].CourseNo[j], &s[i].Grade[j], &s[i].Value[j]);
                            }
                    }
                    //display data from txt file
        printf("\n\n MatricNo\t CourseNo\t Grade\t\t Value");



            for(i=0;i<no;i++)
                {
                         for(j=0; j < nu; j++)
                        {

                            printf("%s %s %s %.2f", s[i].MatricNo, s[i].CourseNo[j], s[i].Grade[j], s[i].Value[j]);
                             }
                }




        printf("\n");






        fclose(fr);

    }

Answer 1

1-您无法写入文件，因为您在 for 循环中的 write() 函数中关闭了 FILE 指针 fw。

2-您无法读取，因为您退出 read() 函数，文件对此代码有效或无效。

if(!fr){
    printf("not file");
    return 0;
}
else
return 1;

3- 只有在 write() 之后调用 read() 函数才能工作。因为如果不先调用 write()，代码就不知道 no 和 nu 的值。

<小时/>

我认为这段代码适合你

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

struct student
{
    char MatricNo[20];
    int matric[20];
    char CourseNo[20];
    int course[20];
    char Grade[20];
    float Value[20];
}
s[10];

int count=0;
int i,j, no,nu;
int write();
int read(int no, int nu);
FILE *fw;

int main()
{
    int choice;
    printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
    printf("Your Choice: ");
    scanf("%i",&choice);
    while(choice!=3)
    {
        switch(choice)
        {
            case 1:
                write();
                break;
            case 2:
                read(no, nu);
                break;
            case 3:
                return 0;
                break;
            default:
                break;
        }
        printf("To record data to txt type <1>\nTo read data from txt type <2>\nTo end the program type <3>\n\n");
        printf("Your Choice: ");
        scanf("%i", &choice);
    }
    fflush(stdin);
    getchar();
    return 0;
}

// for write data to txt file
int write()
{
    fw=fopen("Register Table.txt","w");
    printf("\nEnter number of student :");
    scanf("%d", &no);
    for(i=0;i<no;i++)
    {
        printf("\nEnter student MatricNo :");
        scanf("%s", &s[i].MatricNo);
        printf("\nEnter number of course :");
        scanf("%d", &nu);
        for(j=0; j < nu; j++)
        {
            printf("\nEnter student CourseNo :");
            scanf("%s", &s[i].CourseNo[j]);
            printf("\nEnter student Grade :");
            scanf("%s", &s[i].Grade[j]);
            printf("\nEnter student value :");
            scanf("%f", &s[i].Value[j]);

            fprintf(fw,"%s %s %s %.2f\n", &s[i].MatricNo, &s[i].CourseNo[j], &s[i].Grade[j], &s[i].Value[j]);
        }
    }

    fclose(fw);
}

int read(int no, int nu)
{
    FILE *fr;
    //read data from txt file
    fr=fopen("Register Table.txt","r");
    printf("\n\n\t **Register Table  **\n");
    for(i=0;i<no;i++)
    {
        for(j=0; j < nu; j++)
        {
            fscanf(fr,"%s %s %s %.2f", &s[i].MatricNo, &s[i].CourseNo[j], &s[i].Grade[j], &s[i].Value[j]);
        }
    }
    //display data from txt file
    printf("\n\n MatricNot CourseNot Gradett Value");
    for(i=0;i<no;i++)
    {
        for(j=0; j < nu; j++)
        {
            printf("\n%s %s %s %.2f", &s[i].MatricNo, &s[i].CourseNo[j], &s[i].Grade[j], &s[i].Value[j]);
        }
    }
    printf("\n");
    fclose(fr);
}