Programming-in-C/141217

file2.c

/* File format:
 * Number of couples | record for couple 1                         | record for couple 2...
 *      int          |  No.  | boy name | girl name | next pointer | ...
 *                   |  int  | string   | string    | pointer      |
 */

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

#define NAME_LEN 64

struct couple *createCPLL(FILE *fp);
int file2print(FILE *fp);

int main()
{
    FILE *fp;

    if ((fp = fopen("couple2.out", "w")) == NULL) {
        printf("Can not open this file couple2.txt\n");
        return 0;
    }
    createCPLL(fp);
    fclose(fp);

    if ((fp = fopen("couple2.out", "r")) == NULL) {
        printf("Can not open this file couple2.txt\n");
        return 0;
    }
    file2print(fp);
    fclose(fp);

    return 0;
}

/* declare a struct */
struct couple
{
    int No;
    char boy_name[NAME_LEN];
    char girl_name[NAME_LEN];
    struct couple *next;
};

/* a function to create linked list: tail-insert */
struct couple *createCPLL(FILE *fp)
{
    unsigned int count = 0;
    struct couple *head = (struct couple *)malloc(sizeof(struct couple));
    struct couple *curr;
    memset(head, 0, sizeof(struct couple));

    while (1) {
        struct couple *newcp;
        int No;

        printf("Please input Number of a couple, enter 0 to exit: ");
        scanf("%d", &No);
        if (No == 0)
            break;

        newcp = (struct couple *)malloc(sizeof(struct couple));
        newcp->No = No;
        printf("Boy's name: ");
        scanf("%63s", newcp->boy_name);
        printf("Girl's name: ");
        scanf("%63s", newcp->girl_name);

        ++count;
        newcp->next = head->next;
        head->next = newcp;
    }

    // write file
    fwrite(&count, sizeof(int), 1, fp);
    curr = head->next;
    while (curr != NULL) {
        fwrite(curr, sizeof(struct couple), 1, fp);
        curr = curr->next;
    }

    return head;
}

/* you need a function to printf your linked list to check */
int file2print(FILE *fp)
{
    unsigned int i, count;
    struct couple *head = (struct couple *)malloc(sizeof(struct couple));
    struct couple *curr;
    memset(head, 0, sizeof(struct couple));

    // read file
    fread(&count, sizeof(int), 1, fp);
    for (i = 0; i < count; i++) {
        struct couple *newcp = (struct couple *)malloc(sizeof(struct couple));
        fread(newcp, sizeof(struct couple), 1, fp);
        newcp->next = head->next;
        head->next = newcp;
    }

    // print
    printf("Found %d couples\n", count);
    curr = head->next;
    while (curr != NULL) {
        printf("No.%d couple is %s and %s\n", curr->No, curr->boy_name, curr->girl_name);
        curr = curr->next;
    }

    return 0;
}

有这么几处改进：

1. 文件开头写入 couple 的数目，不要依赖全局变量
2. 使用带“哨兵”的链表，也就是链表 head 是哨兵，不存放实际数据，简化链表操作（不需对首个元素做特殊处理）
3. 读入用户输入时，要防止缓冲区溢出（%63s 而非 %s）
4. 从文件中读入后，把链表的数据结构重新建立起来，而不只是简单打印结果
5. while 循环前面的 printf 语句不需要重复，只要在 while(1) 内加入 break 即可，重复代码是很不好的