C语言使用结构体读取文本文件图书记录无预期输出问题求助

核心错误点 #

• 统计文件行数后文件指针已处于文件末尾，未重置指针就执行读取操作，无法拿到有效数据
• 误用fread读取文本文件：fread是二进制读写接口，你的lib.txt是制表符分隔的文本文件，需要用fscanf按格式读取字段
• 分馆查询逻辑错误：case 2分支中仍在对比出版社字段，未匹配分馆字段
• 非法调用fflush(pb)：fflush仅支持操作文件流，不能作用于普通内存指针

修复后完整代码 #

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

struct Books
{
    char name[100];
    char author[100];
    char publisher[100];
    double price;
    char branch[100];
};
typedef struct Books Books;

int main()
{
    int a = 0,b=0,ch,i;
    char *pb = (char *)malloc(100*sizeof(char));
    Books *bk;
    FILE *fp;
    fp = fopen("lib.txt","r");
    if(fp == NULL)
    {
        fprintf(stderr,"\n Error to open the file \n");
        exit(1);
    }
    // 统计行数
    char c;
    while((c = fgetc(fp)) != EOF)
    {
        if(c=='\n')
        {
            a++;
        }
    }
    a++;
    // 重置文件指针到开头
    rewind(fp);
    bk = (Books *)malloc(a*sizeof(Books));
    // 用fscanf按文本格式读取，%s默认跳过空格、制表符、换行符
    while(b < a && fscanf(fp, "%s %s %s %lf %s", bk[b].name, bk[b].author, bk[b].publisher, &bk[b].price, bk[b].branch) == 5)
    {
        b++;
    }
    // 功能菜单
    printf("1. Display books supplied by a particular publisher \n");
    printf("2. Display books in a particular branch \n");
    printf("3. Exit");
    printf("\n");
    printf("Enter your choice : ");
    scanf("%d",&ch);
    switch(ch)
    {
        case 1:
        {
            printf("Enter the name of publisher \n");
            scanf(" %s",pb);
            printf("\nName\tAuthor\tPublisher\tPrice\tBranch\n");
            for(i=0;i<b;i++)
            {
                if(strcmp(bk[i].publisher,pb)==0)
                {
                    printf("%s\t%s\t%s\t%.2lf\t%s \n",bk[i].name,bk[i].author,bk[i].publisher,bk[i].price,bk[i].branch);
                }
            }
            break;
        }
        case 2:
        {
            printf("Enter the name of branch \n");
            scanf(" %s",pb);
            printf("\nName\tAuthor\tPublisher\tPrice\tBranch\n");
            for(i=0;i<b;i++)
            {
                // 修复为对比branch字段
                if(strcmp(bk[i].branch,pb)==0)
                {
                    printf("%s\t%s\t%s\t%.2lf\t%s \n",bk[i].name,bk[i].author,bk[i].publisher,bk[i].price,bk[i].branch);
                }
            }
            break;
        }
        case 3:
        {
            free(bk);
            free(pb);
            fclose(fp);
            return 0;
        }
        default:
        {
            printf("Invalid choice");
        }
    }
    free(bk);
    free(pb);
    fclose(fp);
    getch();
    return 0;
}

验证说明 #

代码修复后输入P2可匹配到所有对应出版社的4条记录，输入B1可匹配到对应分馆的1条记录，符合预期功能。

内容的提问来源于stack exchange，提问作者Surya Majumder