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Qsort Pointer To Arrays Of Structs

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Qsort Pointer To Arrays Of Structs

 
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  #1
Dec 11th, 2007
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.
C Syntax (Toggle Plain Text) 
  1.   1 #include <stdio.h>
  2.   2 #include <string.h>
  3.   3 #include <stdlib.h>
  4.   4 
  5.   5 typedef struct{
  6.   6         char name[50];
  7.   7         char street[50];
  8.   8         char city_state[50];
  9.   9         int zip;
  10.  10 } ADDRESS;
  11.  11 
  12.  12 void sort(ADDRESS *a, int * i);
  13.  13 ADDRESS* readin(ADDRESS *a, int * i, char *pathin);
  14.  14 void print(ADDRESS *a, int * i, char *pathout);
  15.  15 int compare(const void *p1, const void *p2);
  16.  16 int main(int argc, char * argv[])
  17.  17 {
  18.  18     int *i;
  19.  19 
  20.  20     if(argc == 3){
  21.  21         ADDRESS*a = readin(a, i, argv[1]);
  22.  22         sort(a,i);
  23.  23         print(a, i, argv[2]);
  24.  24     }else{
  25.  25         fprintf(stderr, "Usage: %s <inputfilename> <outputfilename>\n",
  26.  26                 argv[0]);
  27.  27         exit(1);
  28.  28     }
  29.  29 
  30.  30     return 0;
  31.  31 }
  32.  32 ADDRESS *readin (ADDRESS *a, int *i,char *pathin)
  33.  33 {
  34.  34     char buffer[10000];
  35.  35     char temp_zip[50];
  36.  36     char *line;
  37.  37     int count=0;
  38.  38     FILE *fp;
  39.  39     fp = fopen(pathin, "r");
  40.  40     *i = 0;
  41.  41     a = (ADDRESS *)malloc(sizeof(ADDRESS)*50);
  42.  42 
  43.  43 
  44.  44   while (!feof(fp) && (*i < 49))
  45.  45   {
  46.  46 
  47.  47        line = fgets(buffer, 1000, fp);
  48.  48            if(line == NULL)
  49. :set number                                                                                                                                                                            1,1           Top
  50.  92         fputs("\n", fq);
  51.  93         c++;
  52.  94         a++;
  53.  95     }      
  54.  96     fclose(fq);
  55.  97 }
  56.  98 void sort(ADDRESS *a, int *i)
  57.  99 {          
  58. 100     qsort(a, *i, sizeof(ADDRESS),compare);
  59. 101 }       
  60. 102 
  61. 103         
  62. 104 int compare(const void *p1, const void *p2){
  63. 105     const struct ADDRESS *a1 = p1;
  64. 106     const struct ADDRESS *a2 = p2;
  65. 107     if(a1->zip > a2->zip){
  66. 108         return 1;
  67. 109     }else{  
  68. 110         return -1;
  69. 111     }   
  70. 112     return 0;
  71. 113 }
Last edited by Narue; Dec 11th, 2007 at 12:52 pm. Reason: Added code tags
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Re: Qsort Pointer To Arrays Of Structs

 
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  #2
Dec 11th, 2007
Try this

C Syntax (Toggle Plain Text) 
  1. int compare(const void *p1, const void *p2)
  2. {
  3.       const struct ADDRESS *a1 = ( const struct ADDRESS * ) p1 ;
  4.       const struct ADDRESS *a2 = ( const struct ADDRESS * ) p2 ;
  5.  
  6.       if ( a1 -> zip < a2 -> zip)
  7.           return -1 ;
  8.  
  9.       else if ( *a1 == *a2 )
  10.           return 0 ;
  11.  
  12.      else
  13.          return 1 ;
  14.  }
Last edited by AndrewWood; Dec 11th, 2007 at 6:23 am.
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Re: Qsort Pointer To Arrays Of Structs

 
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  #3
Dec 11th, 2007
Thank you, i found that i had to change a few things, notably i had to change my typedef struct to this:


cpp Syntax (Toggle Plain Text) 
  1. typedef [COLOR="Red"]struct pb_s[/COLOR]{
  2.         char name[50];
  3.         char street[50];
  4.         char city_state[50];
  5.         int zip;
  6. } ADDRESS;
  7.  
  8. and then:
  9.  
  10. void sort(ADDRESS *a, int *i)
  11. {
  12.     qsort(a, *i, sizeof(struct pb_s),compare);
  13. }
  14.  
  15.  
  16. int compare(const void *p1, const void *p2){
  17.    const struct pb_s *a1 = p1;
  18.    const struct pb_s *a2 = p2;
  19.     if(a1->zip < a2->zip){
  20.         return -1;
  21.     }else if(a1-> zip == a2->zip){
  22.         return 0;
  23.     }else{
  24.         return 1;
  25.     }
  26. }


making that pb_s at the top of the struct definition is what made it possible to work.
Last edited by WolfPack; Dec 11th, 2007 at 10:24 am. Reason: Added [CODE=CPP][/CODE] Tags
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Re: Qsort Pointer To Arrays Of Structs

 
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  #4
Dec 11th, 2007
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
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