c - 我做错了什么？下面的代码不会将结构化数据的最后一条记录从 .dat 文件复制到 C 中的另一个 .dat 文件

Question

#include<conio.h>

#include<stdio.h>

struct stud

{
  int rollno;
  char name[10];
  char add[10];
};

void main()
{
    struct stud st;

    FILE *fp,*fpp;

    char another='y',ch;

    int a,choice,i;

    printf("***Press 1 to Add record/Create database***\n");

    scanf("%d",&a);

    if(a==1)    /*recording data begins here*/
    {
        fflush(stdin);
        printf("ADD or CREATE NEW?(a/c): ");    /*prompt message to add new record to existing database or to create new database*/
        scanf("%c",&ch);

     if(ch=='a')    /*appending file*/
     {
      add:

      ch='a';

      fp=fopen("Studm.dat","ab");

      while(another=='y' || another=='Y')
      {
        fflush(stdin);

        printf("Enter RollNo. Name & Address\n");

        scanf("%d%s%s",&st.rollno,st.name,&st.add);

        fwrite(&st,sizeof(st),1,fp);

        fflush(stdin);

        printf("\nAdd another record?(y/n): ");    /*prompt message to add another record*/
        scanf("%c",&another);

      }

     }

        if(ch=='c')    /*to create new data file*/
        {

        fp=fopen("Studm.dat","wb");

        printf("Enter RollNo. Name & Address\n");

        scanf("%d%s%s",&st.rollno,st.name,&st.add);

        fwrite(&st,sizeof(st),1,fp);

        fflush(stdin);

        printf("\nAdd another record?(y/n): ");

        scanf("%c",&another);

        fclose(fp);

        if(another=='y' || another=='Y')
        {

         goto add;   /*go to the append file block above*/
        }


    }

      fclose(fp);

    }

每当我在文本编辑器中打开源文件时，给出的所有名称(字符数据)都是可见的，这意味着存储和记录 block 工作正常。

    fflush(stdin);

    printf("\n\nCopying data from studm.dat to stud1.data\n\n");

    fp=fopen("Studm.dat","rb");

    fpp=fopen("Stud1.dat","wb");

    while(fread(&st,sizeof(st),1,fp)==1)    /*loop block to copy data*/
    {
        fflush(stdin);    /*tried every place for flushing the buffer, before and after fwrite with in the loop*/

        fwrite(&st,sizeof(st),1,fpp);

    }
    fclose(fp);

    fclose(fpp);

就像源文件一样，我在执行整个程序代码后在文本编辑器中打开目标文件，直到倒数第二条记录都在那里。

    printf("\n\nCopying done now reading data from file Stud1.dat\n\n");

    fpp=fopen("Stud1.dat","rb");

    while(fread(&st,sizeof(st),1,fp)==1)
    {

     printf("%d %s %s\n",st.rollno,st.name,st.add);

    }

    fclose(fpp);

    getch();
 }

我认为问题出在复制 block 上，但我不知道这是否与缓冲区有关，或者我编码错误或存在错误。

Answer 1

我做了一些更改以避免复杂性。 看在上帝的份上，不要在代码中使用 goto 标签来替换循环。

对于多次编辑，我们深表歉意。这是最终的工作代码。只需编译并执行即可。

#include<stdio.h>

struct stud {
    int rollno;
    char name[100];
    char add[100];
};

void main() {
    struct stud st;
    FILE *fp, *fpp;
    int a, i, i_ret_val, another;
    printf("***Press 1 to Add record/Create database***\n");
    scanf("%d", &a);
    fflush(stdin);
    if (a == 1) /*recording data begins here*/
    {
        /*Since you are using the same file name throughout two cases are not
         * required for adding and creating. Can achieve create in append mode fopen*/
        fp = fopen("Studm.dat", "ab");
        do {
            fflush(stdin);
            printf("Enter RollNo. Name & Address\n");
            scanf("%d%s%s", &st.rollno, &st.name, &st.add);
            printf("Fwrite returned %d\n", fwrite(&st, sizeof(st), 1, fp));
            printf("\nAdd another record?1 for yes: \n"); /*prompt message to add another record*/
            scanf("%d", &another);
        } while (another == 1);
        fclose(fp);
    }
    printf("\nNow Copying the file.\n");
    fp = fopen("Studm.dat", "rb");
    fpp = fopen("Stud1.dat", "wb");
    i_ret_val = fread(&st, sizeof(st), 1, fp);
    while (i_ret_val == 1) {
        i_ret_val = fwrite(&st, sizeof(st), 1, fpp);
        i_ret_val = fread(&st, sizeof(st), 1, fp);
    }
    fclose(fp);
    fclose(fpp);
    printf("\n\nCopying done. Now reading data from file Stud1.dat\n\n");
    fpp = fopen("Stud1.dat", "rb");
    i_ret_val = fread(&st, sizeof(st), 1, fpp);
    printf("\nRetrieved from database\n");
    while (i_ret_val == 1) {
        printf("Roll No: %d, Name: %s, Address:%s\n", st.rollno, st.name,
                st.add);
        i_ret_val = fread(&st, sizeof(st), 1, fpp);
    }
    fclose(fpp);
}