使用文件和结构的 C 程序

Question

我想知道为什么代码不打印输出。二进制文件模式和普通文件模式有什么区别？

#include<stdio.h>
#include <stdlib.h>
typedef struct book_details
{ 
  char book_title[50];
  int book_no;
  float book_price;
}book_details;

int main()
{
  book_details b;
  FILE *fp;

  fp = fopen("book_list.txt","w+");
  if (fp == NULL)
      printf("File not found");

  fflush(stdin);
  printf("Enter Book Title: \n");
  gets(b.book_title);
  printf("Enter Book ID Number: \n");
  scanf("%d",&b.book_no);
  printf("Enter Book Price: \n");
  scanf("%f",&b.book_price);
  fprintf(fp,"Here are the book details");
  fwrite(&b,sizeof(b),1,fp);
  while (fread(&b,sizeof(b),1,fp) > 0)
      printf("%s %d %f\n",b.book_title,b.book_no,b.book_price);
  fclose(fp);
 }

有哪些错误？

Answer 1

发生这种情况是因为这里使用相同的文件指针 fp 进行读取和写入。您的输出文件是二进制文件，因此只有 fread() 和 fwrite( ) 可以在这里使用。在这种情况下，您不能使用fprintf(fp,"Here are the book details");。这也会导致阅读错误。在这种情况下，有两个解决方案。

1. Using rewind().

使用函数rewind()，我们可以将文件指针fp倒回到初始状态以读取文件。

试试这个代码:-

#include<stdio.h>
#include <stdlib.h>
typedef struct book_details
{ 
  char book_title[50];
  int book_no;
  float book_price;

}book_details;

int main()
{
  book_details b;
  FILE *fp;

  fp = fopen("book_list.txt","r+");
  if (fp == NULL)
     printf("File not found");

  printf("Enter Book Title: \n");
  gets(b.book_title);
  printf("Enter Book ID Number: \n");
  scanf("%d",&b.book_no);
  printf("Enter Book Price: \n");
  scanf("%f",&b.book_price);            // removed fprintf();
  fwrite(&b,sizeof(b),1,fp);
  fflush(stdin);

  rewind(fp);                        // Using rewind();

  while (fread(&b,sizeof(b),1,fp) > 0)
     printf("%s %d %f\n",b.book_title,b.book_no,b.book_price);
  fclose(fp);
 }

2. Using separate read and write FILE pointers.

试试这个代码:-

#include<stdio.h>
#include <stdlib.h>
typedef struct book_details
{ 
  char book_title[50];
  int book_no;
  float book_price;

}book_details;

int main()
{
  book_details b;
  FILE *fpwrite,* fpread;                 // separate File pointers. 

  fpwrite = fopen("book_list.txt","w");
  if (fpwrite == NULL)
     printf("File not found");

  printf("Enter Book Title: \n");
  gets(b.book_title);
  printf("Enter Book ID Number: \n");
  scanf("%d",&b.book_no);
  printf("Enter Book Price: \n");
  scanf("%f",&b.book_price);                 // removed fprintf();
  fflush(stdin);
  fwrite(&b,sizeof(b),1,fpwrite);
  fclose(fpwrite);

  fpread = fopen("book_list.txt","r");
  while (fread(&b,sizeof(b),1,fpread) > 0)
     printf("%s %d %f\n",b.book_title,b.book_no,b.book_price);
  fclose(fpread);
 }

单独的文件指针被认为更好，因为它提高了源代码的可读性。