C语言feof+fgets循环重复计数门禁记录问题求助

我有一份2020年办公室门禁记录文本文件，约2万行，每条记录格式固定：

• 索引[0-3]：无效数据
• 索引[4-9]：Badge ID
• 索引[10]：进出标识（0进1出）
• 索引[11-18]：日期
• 索引[19-22]：时分
• 索引[23-26]：Gate ID

编写了C语言代码统计指定Badge ID的出门（entry=1）次数，但结果出现重复计数——比如统计Badge ID 002341时得到342次，实际应为171次。原代码如下：

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

#define NUMLEN 27

int main () {
    printf("\n-- 32bit version\n");
    int entriesCounter = 0;
    char buff[NUMLEN];
    char requiredBadge[7];
    char badge[7];
    char entry[2];
    char day[3];
    char month[3];
    char year[5];
    char hours[3];
    char minutes[3];
    char gate[4];
    FILE *fp;
    fp = fopen("Storico2020.txt", "r");
    if (fp == NULL) {
        printf("Error open");
        exit(1);
    }
    printf("\nInsert ID badge for counting accesses: ");
    scanf("%s", requiredBadge);
    while(!feof(fp)) {
        fgets(buff, NUMLEN, fp);    // example -> init:0000 | badge:000352 | entry:1 | data:01012019 | time:0030 | gate:023
        strncpy(badge, buff+4, 6);
        badge[6] = '\0';
        strncpy(entry, buff+10, 1);
        entry[1] = '\0';
        strncpy(day, buff+11, 2);
        day[2] = '\0';
        strncpy(month, buff+13, 2);
        month[2] = '\0';
        strncpy(year, buff+15, 4);
        year[4] = '\0';
        strncpy(hours, buff+19, 2);
        hours[2] = '\0';
        strncpy(minutes, buff+21, 2);
        minutes[2] = '\0';
        strncpy(gate, buff+23, 3);
        gate[3] = '\0';
        if (strcmp(requiredBadge, badge) == 0 && strcmp(entry, "1") == 0) {
            printf("\nBadge: %s | in date: %s/%s/%s | gate: %s | hour: %s:%s", badge, day, month, year, gate, hours, minutes);
            entriesCounter++;
        }
        
    }
    fclose(fp);
    printf("\n********** TOTAL ACCESSES OF BADGE ID %s: %d ***************\n" ,requiredBadge, entriesCounter);
    
    system("PAUSE");

    return 0;
}

问题根源 #

1. while(!feof(fp))循环条件错误：feof()仅在尝试读取并到达文件末尾时返回真，导致最后一行有效数据读取完成后，循环会额外执行一次。此时fgets()读取失败，buff保留上一次的内容，最后一条符合条件的记录会被重复统计。
2. 缓冲区长度不足：代码中NUMLEN定义为27，但注释里的示例行长度远超过27。fgets()每次只能读取26个字符（需预留1位给终止符\0），剩余内容留在输入缓冲区，下一次循环继续读取同一行的剩余部分，同一条记录被拆分成多次处理，最终计数翻倍。

解决步骤 #

• 修正循环条件：将while(!feof(fp))改为while(fgets(buff, sizeof(buff), fp) != NULL)，当fgets()读取失败（到达末尾或出错）时直接退出循环，避免重复处理。
• 增大缓冲区：将NUMLEN调整为足够容纳完整行的数值，比如#define NUMLEN 100，确保能读取整条记录。
• 可选验证：检查buff最后一个字符是否为\n，若不是则说明该行被截断，可添加跳过或报错逻辑。

修正后的代码 #

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

#define NUMLEN 100  // 增大缓冲区以容纳完整记录行

int main () {
    printf("\n-- 32bit version\n");
    int entriesCounter = 0;
    char buff[NUMLEN];
    char requiredBadge[7];
    char badge[7];
    char entry[2];
    char day[3];
    char month[3];
    char year[5];
    char hours[3];
    char minutes[3];
    char gate[4];
    FILE *fp;
    fp = fopen("Storico2020.txt", "r");
    if (fp == NULL) {
        printf("Error open");
        exit(1);
    }
    printf("\nInsert ID badge for counting accesses: ");
    scanf("%s", requiredBadge);
    
    // 用fgets返回值判断读取是否成功，替代feof循环
    while(fgets(buff, NUMLEN, fp) != NULL) {    
        strncpy(badge, buff+4, 6);
        badge[6] = '\0';
        strncpy(entry, buff+10, 1);
        entry[1] = '\0';
        strncpy(day, buff+11, 2);
        day[2] = '\0';
        strncpy(month, buff+13, 2);
        month[2] = '\0';
        strncpy(year, buff+15, 4);
        year[4] = '\0';
        strncpy(hours, buff+19, 2);
        hours[2] = '\0';
        strncpy(minutes, buff+21, 2);
        minutes[2] = '\0';
        strncpy(gate, buff+23, 3);
        gate[3] = '\0';
        
        if (strcmp(requiredBadge, badge) == 0 && strcmp(entry, "1") == 0) {
            printf("\nBadge: %s | in date: %s/%s/%s | gate: %s | hour: %s:%s", badge, day, month, year, gate, hours, minutes);
            entriesCounter++;
        }
    }
    fclose(fp);
    printf("\n********** TOTAL ACCESSES OF BADGE ID %s: %d ***************\n" ,requiredBadge, entriesCounter);
    
    system("PAUSE");

    return 0;
}

内容的提问来源于stack exchange，提问作者sirducas