How to sort my array of char pointers

Question

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>

for the program I have an array of char * named arr[] and I am trying to sort it alphabetically but having no luck doing so it does nothing when running the for loop at the end. I want to keep the offset[] with arr[] so because I need the char code and the offset for a file

typedef struct country {
    char code_name[4];
    char name[45];
    int population;
    float life_expect;
}country;

country data[240];

int main(void) {

    char *swap;
    int a=0,c=0,d=0,n=0;
    int cmp = 1;

heres the arr[]

    char *arr[239];
    size_t offset[239];
    char *ptr;
    int i = 0;
    int temp;
    char buf[512];
    char *token;
    char buf_write[10000];
    size_t nbytes_written;  
    size_t t_nbytes;

    FILE *fptr;
    fptr = fopen("AllCountries.dat", "r");
    int wptr;
    wptr = open("BinaryAllCountries.dat", O_RDWR);
    FILE *rptr;
    rptr = fopen("BinaryAllCountries.dat", "r");    

    do {
        if (fgets(buf, 512 , fptr)){
            //printf("%s\n",buf);
            token = strtok(buf,",;");
            while (token != NULL){          
            token = strtok(NULL, ",;");
                if (temp == 0){
                strcpy(data[i].code_name, token);
                nbytes_written = write(wptr, token, strlen(token));
                t_nbytes = t_nbytes + nbytes_written;
                //printf("code_name: %s\n", data[i].code_name);
                }
                if (temp == 1){
                strcpy(data[i].name, token);
                cmp = strcmp(data[i].name, "Virgin Islands");
                nbytes_written = write(wptr, token, strlen(token));
                t_nbytes = t_nbytes + nbytes_written;
                //printf("name: %s\n", data[i].name);
                } 
                if (temp == 6){ 
                data[i].population = atoi(token);
                nbytes_written = write(wptr, token, strlen(token));
                t_nbytes = t_nbytes + nbytes_written;
                //printf("population: %i\n", data[i].population);
                }
                if (temp == 7){
                data[i].life_expect = atof(token);
                nbytes_written = write(wptr, token, strlen(token));
                t_nbytes = t_nbytes + nbytes_written;
                //printf("life expectancy: %f\n", data[i].life_expect);
                }
            temp = temp + 1;
            }
        arr[i] = data[i].code_name;
        offset[i] = t_nbytes;
/*
        printf("%s\n",arr[i]);
        printf("%lu\n", offset[i]);
*/      printf("--------\n");

        i = i + 1;
        temp = 0;
        }
    }while (!feof(fptr));

here is where I tried to sort the array but nothing happens and the array stays the same

    for (c = 0 ; c < 10; c++){
            for (d = 0 ; d < 238; d++){
                if (arr[d] > arr[d+1]){
                swap     = arr[d];
                arr[d]   = arr[d+1];
                arr[d+1] = swap;
                }
        }
    }
    for (i = 0; i <239; i++){
        printf("%s\n",arr[i]);
    }

here is what some of the output looks like from the arr[] as you can see it doesn't get sorted

DZA AGO BEN BWA IOT BFA BDI CMR CPV CAF TCD COM COG COD CIV DJI EGY GNQ ERI ETH GAB GMB GHA GIN GNB KEN LSO LBR LBY MDG MWI MLI MRT

i want to keep the offset[] array associated with the char arr[] as i need them for a file — jhowe
– jhowe, Commented Jan 28, 2017 at 19:42
then define a struct with a char * and a size_t (or off_t, if it is a file offset) members, use an array of such structs, and sort it with qsort() and your own comparison function. The man 3 bsearch man page has an example of qsorting an array of structs. — Nominal Animal
– Nominal Animal, Commented Jan 28, 2017 at 19:50
so i can just add a size_t to my stuct and i can then qsort? — jhowe
– jhowe, Commented Jan 28, 2017 at 19:55

jhowe · Accepted Answer · 2017-01-29 18:48:28Z

2

heres what i did and that allowed me to sort the struct based on the code_name field

static int
compmi(const void *m1, const void *m2)
       {
           struct country *mi1 = (struct country *) m1;
           struct country *mi2 = (struct country *) m2;
           return strcmp(mi1->code_name, mi2->code_name);
       }


  typedef struct country {
        char code_name[4];
        char name[45];
        int population;
        float life_expect;
        size_t offset;
    }country;

qsort(data, sizeof(data)/sizeof(data[0]),sizeof(struct country),compmi);

edited Jan 29, 2017 at 18:48

answered Jan 28, 2017 at 21:28

jhowe

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2 Comments

alk Over a year ago

What is compmi?

jhowe Over a year ago

oh sorry forgot that will put it in now

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