c - 将结构保存在文件中

Question

我正在编写一个程序，将联系人列表保存在文件结构中。我已经尝试了很多方法，但是当我尝试将文件读取到程序时，它没有读取任何内容。

这是我的程序，没有打开文件并保存到文件:

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

struct agenda {
    int idContacte;
    char name[50];
    struct agenda *nextContacte;
};
struct agenda *pAgenda;
struct agenda *pFirst = NULL;
struct agenda *pIndex;

void insert();
void show();

int main()
{
    //Menu
    int opc;
    while(1){
        printf("1.Insert Contact.\n");
        printf("2.Show Contacts.\n");
        printf("3.Exit\n");
        scanf("%d", &opc);
        switch(opc){
            case 1:
                insert();
                break;
            case 2:
                show();
                break;
            case 3:
                return 0;
        }
    }
}
void insert(){
    pAgenda = (struct agenda *)malloc(sizeof(struct agenda));
    printf("Insert ID: ");
    scanf("%d", &pAgenda->idContacte);
    printf("Insert the name: ");
    scanf("%s", pAgenda->name);
    printf("\n");
    if (pFirst==NULL || pAgenda->idContacte < pFirst->idContacte)
    {
        pAgenda->nextContacte=pFirst;
        pFirst=pAgenda;
    }
    else if (pAgenda->idContacte > pFirst->idContacte){
        pIndex=pFirst;
        while(pIndex->nextContacte && pIndex->nextContacte->idContacte < pAgenda->idContacte)
        {
            pIndex = pIndex->nextContacte;
        }
        pAgenda->nextContacte = pIndex->nextContacte;
        pIndex->nextContacte = pAgenda;
    }
}
void show(){
    pIndex = pFirst;
    while(pIndex && pIndex->idContacte <= 100) {
        printf("\nID: %d", pIndex->idContacte);
        printf("\nNAME: %s", pIndex->name);
        printf("\n\n");
        pIndex = pIndex->nextContacte;
    }
}

你能帮助我如何在程序启动时从文件中获取联系人，然后在插入联系人时重写文件并在文件中再次插入所有联系人吗？

Answer 1

当你结束程序时，你应该执行以下操作

int save_list(struct agenda *head) {
  FILE *save = fopen("file.name", "wb");
  if(!save) return -1;

  while(head) {
    fwrite(head, sizeof *head - sizeof head, 1, save);
    head = head->nextContacte;
  }

  fclose(save);
  /* Somebody would free list memory after this function execution */
  return 0;
}

在程序开始时，您应该执行以下操作

struct agenda *restore_list() {
  FILE *restore= fopen("file.name", "rb");
  struct agenda *head = NULL;
  struct agenda *cur = head;
  struct agenda temp;
  if(!restore) return head;

  while( fwrite(&temp, sizeof temp - sizeof head, 1, save) == 1) {
    struct agenda *node = malloc( sizeof(struct agenda) );
    if(NULL == node) {
      /* Handle out of memory error here, free list */
      return NULL;
    }
    *node = temp;
    node->nextContacte = NULL;
    if(head) {
      cur->nextContacte = node;
      cur = node;
    } else {
       /* First node */
       head = cur = node;
    }
  }

  fclose(restore);
  return head;
}