从二进制文件中读取fread（）的意外行为

Question

该程序基本上创建了所有信息的航班列表（由来自ListaVoli.bin的fread（）函数读取）。 该列表主要由节点组成，每个节点包含一个航班。

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

#define FILE_NAME "/Users/Matt/Downloads/ListaVoli.bin" 

struct flight { 
    int flightCode; 
    char destination[3]; 
    int scheduledDepHour; 
    int scheduledDepMinute; 
    int realDepHour; 
    int realDepMinute; 
    int passengers; 
}; 

struct node { 
    struct flight volo; 
    struct node *next; 
}; 

struct node *addToList(struct node *list, struct flight voloIn) { 
    struct node *newNode; 
    newNode = malloc(sizeof(struct node)); 

    if (newNode == NULL) { 
     printf("Error: malloc failed\n"); 
     exit(EXIT_FAILURE); 
    } 

    newNode -> volo = voloIn; 
    newNode -> next = list; 
    return newNode; 
} 

void printList(struct node *list) { 
    for (; list != NULL; list = list -> next) { 
     printf("Code:%d\nDestination:%s\nDeparture:%d-%d\nReal:%d-%d\nPassengers:%d\n\n\n", 
     list -> volo.flightCode, 
     list -> volo.destination, 
     list -> volo.scheduledDepHour, 
     list -> volo.scheduledDepMinute, 
     list -> volo.realDepHour, 
     list -> volo.realDepMinute, 
     list -> volo.passengers 
     ); 
    } 
} 

void decolla(struct node *list, int flightCode, int realDepHour, int realDepMinute) { 
    for (; list != NULL; list = list -> next) { 
     if (flightCode == (list -> volo.flightCode)) { /* 
      printf("Inserisci ora di partenza per il volo %d: ", flightCode); 
      scanf("%d", &(list -> volo.realDepHour)); 
      printf("Inserisci minuto di partenza: "); 
      scanf("%d", &(list -> volo.realDepMinute)); */ 
      list -> volo.realDepHour = realDepHour; 
      list -> volo.realDepMinute = realDepMinute; 
     } 
    } 
} 

void delay(struct node *list) { 
    for (; list != NULL; list = list -> next) { 
     if ((list -> volo.realDepHour) - (list -> volo.scheduledDepHour) == 0) { 
      if ((list -> volo.realDepMinute) - (list -> volo.scheduledDepMinute) > 5 && (list -> volo.realDepMinute) - (list -> volo.scheduledDepMinute) < 30) { 
      printf("Il volo %d ha più di 5 minuti di ritardo\n", list -> volo.flightCode); 
      continue; 
      } 
      if ((list -> volo.realDepMinute) - (list -> volo.scheduledDepMinute) > 30) { 
       printf("Il volo %d ha più di 30 minuti di ritardo\n", list -> volo.flightCode); 
       continue; 
      } 
     } else 
      printf("Il volo %d ha più di 30 minuti di ritardo\n", list -> volo.flightCode); 
    } 
} 

void passengersCount(struct node *list) { 
    for (; list != NULL; list = list -> next) { 
     if (list -> volo.passengers > 200) { 
      printf("Il volo %d ha più di 200 passeggeri\n", list -> volo.flightCode); 
      continue; 
     } 
    } 
} 

int main() { 
    FILE *fp; 
    struct node *first = NULL; 
    struct flight volo; 

    /* Apro il file e controllo che sia stato aperto correttamente */ 
    if ((fp = fopen(FILE_NAME, "rb")) == NULL) { 
     printf("Can't open %s\n", FILE_NAME); 
     exit(EXIT_FAILURE); 
    } 

    for (int i = 0; i < 4; i++) { 
     fread(&volo, sizeof(int), 7, fp); 
     first = addToList(first, volo); 
    } 

    decolla(first, 3497, 11, 30); 
    decolla(first, 2193, 11, 53); 
    decolla(first, 4284, 11, 07); 
    decolla(first, 5536, 12, 26); 
    printList(first); 
    delay(first); 
    passengersCount(first); 

    /* Controllo che il file sia chiuso correttamente */ 
    if (fclose(fp) == EOF) { 
     printf("File not closed properly!"); 
     exit(EXIT_FAILURE); 
    } 
    return 0; 
} 

代码编译正确，所以不用担心整个代码，只关注main（）函数和两个结构体。 我有一个关于在main（）函数FREAD（）函数的两个问题：

1. 为什么，如果我把的sizeof（int）的第二个参数，该flight.destination值正确分配？不应该char [3]变量比sizeof（int）大吗？
2. 为什么，如果我把sizeof（struct flight）作为第二个参数（这将是最好的选择），我会得到分段错误：11？

Answer 1

三个字符的数组是三个字节。一个int通常（至少在现代32位和64位平台上）4个字节。它的工作原理是读取sizeof(int)，因为编译器添加了填充。

但“正确”（或至少是平常）的方式来读取结构将是你的情况下，使用sizeof(volo)读取整个结构为一个单元，即：

fread(&volo, sizeof(volo), 1, fp); 

如果你得到其他因为这个错误，你正在做点什么否则错了。