Question

I have a simple program that list files written in C. I’m just wondering what can I add to this code so the files print out in sorted order? Thanks

while ((directory = readdir(dir)) != NULL)
{
   printf("%s\n", directory->dir_name);
}

Answer 1

You have first to store the names in an array, MAXDIRS is the max number of dirs (or you could use calloc to allocate dynamically the array)

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

char dirs[MAXDIRS][512]; // you have to ensure correct allocation (eg names < 512 chars)
int ndirs = 0; // number of dirs

while ((directory = readdir(dir)) != NULL) {
   strcpy(dirs[ ndirs++ ], directory->d_name);
}

// Then sort the directories

// need a sorting function
int comp(void const *a, void const *b) { 
    char const *u = (char const *)a;
    char const *v = (char const *)b;

    return strcmp(u, v);
}

// use qsort to sort the dirs
qsort (dirs, ndirs, sizeof(dirs[0]), comp);

dirs now contains a sorted array of directories

// display

int i;

for (i=0 ; i<ndirs ; i++) {
  printf("%s\n", dirs[i]);
}