c - How to sort file output? -

i have program takes user input , creates records several fields user enters. user asked enter first , last name of person, address, city, state, zipcode, , phone #. i'm trying sort records in alphabetical order in relation city of each record. how go this, i'm pretty stumped on how sort based on 1 variable , print entire record properly.

#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** 

i tried use qsort(). ended fatal error. on top of that, how print entire record when i'm able sort 1 field?

#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 = 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 record info              printf("are there anymore records? [y/n] ");             scanf(" %c", &answer);           if(tolower(answer) == 'y')         {             i++;             count++;         }          for(i = 0; < 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; } 

as is, have list structure, cannot sorted qsort(), can use array instead, , allocate dynamically using malloc() + realloc().

to sort entries can use qsort(), example suppose want sort first name, then

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);  } 

and then

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