Qsort Pointer To Arrays Of Structs

[stolson]

I have read in a file, and i can print it out successfully, but i must sort the pointer to the array of structures. below is my code. I must sort the phone book in ascending order by zip code. If anyone could please help that would be great.

1 #include <stdio.h>
  2 #include <string.h>
  3 #include <stdlib.h>
  4 
  5 typedef struct{
  6         char name[50];
  7         char street[50];
  8         char city_state[50];
  9         int zip;
 10 } ADDRESS;
 11 
 12 void sort(ADDRESS *a, int * i);
 13 ADDRESS* readin(ADDRESS *a, int * i, char *pathin);
 14 void print(ADDRESS *a, int * i, char *pathout);
 15 int compare(const void *p1, const void *p2);
 16 int main(int argc, char * argv[])
 17 {
 18     int *i;
 19 
 20     if(argc == 3){
 21         ADDRESS*a = readin(a, i, argv[1]);
 22         sort(a,i);
 23         print(a, i, argv[2]);
 24     }else{
 25         fprintf(stderr, "Usage: %s <inputfilename> <outputfilename>\n",
 26                 argv[0]);
 27         exit(1);
 28     }
 29 
 30     return 0;
 31 }
 32 ADDRESS *readin (ADDRESS *a, int *i,char *pathin)
 33 {
 34     char buffer[10000];
 35     char temp_zip[50];
 36     char *line;
 37     int count=0;
 38     FILE *fp;
 39     fp = fopen(pathin, "r");
 40     *i = 0;
 41     a = (ADDRESS *)malloc(sizeof(ADDRESS)*50);
 42 
 43 
 44   while (!feof(fp) && (*i < 49))
 45   {
 46 
 47        line = fgets(buffer, 1000, fp);
 48            if(line == NULL)
:set number                                                                                                                                                                            1,1           Top
 92         fputs("\n", fq);
 93         c++;
 94         a++;
 95     }      
 96     fclose(fq);
 97 }
 98 void sort(ADDRESS *a, int *i)
 99 {          
100     qsort(a, *i, sizeof(ADDRESS),compare);
101 }       
102 
103         
104 int compare(const void *p1, const void *p2){
105     const struct ADDRESS *a1 = p1;
106     const struct ADDRESS *a2 = p2;
107     if(a1->zip > a2->zip){
108         return 1;
109     }else{  
110         return -1;
111     }   
112     return 0;
113 }

[AndrewWood]

Try this

int compare(const void *p1, const void *p2)
{
      const struct ADDRESS *a1 = ( const struct ADDRESS * ) p1 ;
      const struct ADDRESS *a2 = ( const struct ADDRESS * ) p2 ;

      if ( a1 -> zip < a2 -> zip)
          return -1 ;

      else if ( *a1 == *a2 )
          return 0 ;

     else
         return 1 ;
 }

[stolson]

Thank you, i found that i had to change a few things, notably i had to change my typedef struct to this:

typedef struct pb_s{
        char name[50];
        char street[50];
        char city_state[50];
        int zip;
} ADDRESS;

and then:

void sort(ADDRESS *a, int *i)
{
    qsort(a, *i, sizeof(struct pb_s),compare);
}


int compare(const void *p1, const void *p2){
   const struct pb_s *a1 = p1;
   const struct pb_s *a2 = p2;
    if(a1->zip < a2->zip){
        return -1;
    }else if(a1-> zip == a2->zip){
        return 0;
    }else{
        return 1;
    }
}

making that pb_s at the top of the struct definition is what made it possible to work.

[AndrewWood]

Good I'm glad you got the problem...sorted, har har.

Not sure if your compiler supports it but another thing you can do is

struct ADDRESS {
         char name[50];
         char street[50];
         char city_state[50];
         int zip;
 } ;

if you are going to use it locally

If you want to share it between modules you can put it in a header file as

volatile struct ADDRESS {
} address ;

so on & so forth