Sample of code in C to sort large folders according to last modification.

sort.c

/* 
Benchmark:
gabriel@localhost:~ $ ls ~/.mail/INBOX/cur | wc -l
8543
gabriel@localhost:~ $ time ./sort ~/.mail/INBOX/cur > output
real    0m0.022s
user    0m0.000s
sys     0m0.024s
*/
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
struct File{
  int time,id;
};
time_t get_st_mtime(const char *file_name) {
  struct stat buf;
  if (stat(file_name, &buf) != 0 ) return 0;
  return buf.st_mtime;
}
struct File *File_create(int id, int time){
  struct File *file = malloc(sizeof(struct File));
  file->id = id;
  file->time = time; 
  return file; 
}

void *File_destroy(struct File *file){
  free(file);
}

int cmpfunc(const void * a, const void * b){
  struct File *a1 = *(struct File * const *)a;
  struct File *b1 = *(struct File * const *)b;
  return (b1->time-a1->time);
}

int main(int argc,char *argv[]){
  struct dirent **namelist;
  int n,c=0,d,swap,i=0,f,s;
  char *ch;
  n = scandir(argv[1], &namelist, 0, NULL);
  struct File **files = malloc(n*sizeof(struct File));
  while (n--) {
    ch = namelist[n]->d_name;
    if (strcmp(ch, ".") == 0 || strcmp(ch, "..") == 0){
      free(namelist[n]);
      continue;
    }
    struct File *file = File_create(n, get_st_mtime(ch));
    files[c] = file;
    c++;
  }
  qsort(files, c, sizeof(struct File *), cmpfunc);
  for (i=0;i<c;i++){
    printf("%s\n", namelist[files[i]->id]->d_name);
    free(namelist[files[i]->id]);
    free(files[i]);
  }
  free(files);
  free(namelist);
  return 0;
}