c - 如何排序文件输出？

Question

我有一个程序接受用户输入并创建包含用户输入的多个字段的记录。要求用户输入人员的名字和姓氏、地址、城市、州、邮政编码和电话号码。我正在尝试根据每条记录的城市按字母顺序对记录进行排序。我该怎么做，我很困惑如何根据一个变量进行排序，然后正确打印整个记录。

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

typedef struct Record Record;

struct Record
    {
        char fname[51];
        char lname[51];
        char address[51];
        char city[51];
        char state[51];
        char zipcode[51];
        char phoneNumber[51];

        Record *next;
    };


int main()
{
    FILE *fileWriter;
    const char filename[] = "data.txt";
    char answer = '\0';
    Record *records = NULL;
    Record *records_first = NULL;
    Record *records_previous = NULL;

    fileWriter = fopen(filename,"wt");

    if(fileWriter != NULL) {

        for( ; ; ) {
            records = (Record*) malloc(sizeof(Record));  

            if(records_first == NULL)
                records_first = records;

            if(records_previous != NULL)
                records_previous->next = records;

            records = records_first;
            printf("First Name: \n");
            scanf("%s", records->fname);
            fprintf(fileWriter,"%s\t",records->fname);

            printf("Last Name: \n");
            scanf("%s", records->lname);
            fprintf(fileWriter,"%s\t",records->lname);

            printf("Address: \n");
            scanf(" %[^\n]", records->address);
            fprintf(fileWriter,"%s\t",records->address);

            printf("City: \n");
            scanf("%s", records->city);
            fprintf(fileWriter,"%s\t",records->city);

            printf("State: \n");
            scanf("%s", records->state);
            fprintf(fileWriter,"%s\t",records->state);

            printf("Zipcode: \n");
            scanf("%s", records->zipcode);
            fprintf(fileWriter,"%s\t",records->zipcode);

            printf("Phone Number: \n");
            scanf("%s", records->phoneNumber);
            fprintf(fileWriter,"%s\t\n",records->phoneNumber);

            records->next = NULL;
            records_previous = records;

            printf("Are there anymore records? [y/n] ");
            scanf(" %c", &answer);

            if(tolower(answer) != 'y') {
                free(records);
                fclose(fileWriter);
                break;
            }
        }

    } else
        printf("Error opening file.");

    return 0;
}

                        **Edited Version**

我尝试使用 qsort()。但最终出现了 fatal error 。最重要的是，当我只能对一个字段进行排序时，如何正确打印整条记录？

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

struct Record
    {
        char fname[51];
        char lname[51];
        char address[51];
        char city[51];
        char state[51];
        int zipcode;
        int phoneNumber;
    };

int compare_city(const void *const p1, const void *const p2)
 {
    struct Record *r1 = (struct Record *) p1;
    struct Record *r2 = (struct Record *) p1;

    return strcmp(r1->city, r2->city);
 }


int main()
{
    FILE *fileWriter;
    const char filename[] = "data.txt";
    char answer = 'y';
    int size = 1;
    int i = 0;
    int count = 1;
    struct Record *records = NULL;
    struct Record *records_temp = NULL;


    fileWriter = fopen(filename,"wb");
    if(fileWriter != NULL)
        while(answer == 'y' || answer == 'Y')
        {
            if(records_temp == NULL)
            {
                struct Record *records_temp = realloc(records,(size)*sizeof(*records));
            }

            records = records_temp;
            printf("First Name: \n");
            scanf("%s", records[i].fname);


            printf("Last Name: \n");
            scanf("%s", records[i].lname);


            printf("Address: \n");
            scanf(" %[^\n]", records[i].address);


            printf("City: \n");
            scanf("%s", records[i].city);


            printf("State: \n");
            scanf("%s", records[i].state);


            printf("Zipcode: \n");
            scanf("%s", records[i].zipcode);


            printf("Phone Number: \n");
            scanf("%s", records[i].phoneNumber);

            //stores all record info

            printf("Are there anymore records? [y/n] ");
            scanf(" %c", &answer);


        if(tolower(answer) == 'y')
        {
            i++;
            count++;
        }

        for(i = 0; i < count ; i++)
        {
            qsort(records, count, sizeof(struct Record), compare_city);
            fprintf(fileWriter,"%s\n",records[i].fname);
            fprintf(fileWriter,"%s\n",records[i].lname);
            fprintf(fileWriter,"%s\n",records[i].address);
            fprintf(fileWriter,"%s\n",records[i].city);
            fprintf(fileWriter,"%s\n",records[i].state);
            fprintf(fileWriter,"%d\n",records[i].zipcode);
            fprintf(fileWriter,"%d\n",records[i].phoneNumber);
        }

        free(records);
    }
    return 0;
}

Answer 1

照原样，你有一个列表结构，不能用 qsort() 排序, 但您可以改用数组，并使用 malloc() 动态分配它+ realloc() .

要对条目进行排序，您可以使用 qsort() ，例如假设你想按名字排序，然后

int compare_first_name(const void *const p1, const void *const p2)
 {
    struct Record *r1 = (struct Record *) p1;
    struct Record *r2 = (struct Record *) p1;

    return strcmp(r1->fname, r2->fname);
 }

然后

qsort(base, count, sizeof(struct Record), compare_first_name);