#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* #include "xmalloc.h" */
#define xmalloc malloc
#define xfree free
#define xrealloc realloc

#define BUFFSIZE 3 /* >= 2 */
char *mygetline(FILE *fp) {
  static char inbuff[BUFFSIZE];
  char *outbuff_malloc, *tmpbuff;
  char *p, *r;
  int fEOL;

  if ((outbuff_malloc = xmalloc(1)) == NULL) {
    return NULL;
  }
  *outbuff_malloc = '\0';
  fEOL = 0;
  do {
    r = fgets(inbuff, BUFFSIZE, fp);
    if (r == NULL)
      break;
    for (p = inbuff; *p != '\0'; p++)
      ;
    if (*(p - 1) == '\n')
      fEOL = 1;
    if ((tmpbuff = xrealloc(outbuff_malloc, strlen(outbuff_malloc) + strlen(inbuff) + 1)) == NULL) {
      xfree(outbuff_malloc);
      return NULL;
    }
    strcat(tmpbuff, inbuff);
    outbuff_malloc = tmpbuff;
  } while (!fEOL);
  if (strlen(outbuff_malloc) > 0) {
    for (p = outbuff_malloc; *p != '\0'; p++)
      ;
    if (*(p - 1) == '\n')
      *(p - 1) = '\0';
    return outbuff_malloc;
  }
  xfree(outbuff_malloc);
  return NULL;
}

static int flagS = 0;

struct node {
  void *data;
  struct node *left;
  struct node *right;
};

void push(struct node **root, void *data, int (*cmp)(void *, void *)) {
  struct node *p;
  if (!*root) {
    if ((p = xmalloc(sizeof(struct node))) == NULL) {
      fprintf(stderr, "cannot allocate enough memory(struct node), aborted\n");
      exit(-1);
    }
    p->data = data;
    p->left = p->right = NULL;
    *root = p;
    return;
  } 
  if ((*cmp)(data, (*root)->data) < 0) {
    push(&((*root)->left), data, cmp);
  } else {
    push(&((*root)->right), data, cmp);
  }
}

void *pop(struct node **root) {
  struct node *p;
  void *data;
  if (*root == NULL) {
    return NULL;
  }
  if ((*root)->left) {
    data = pop(&((*root)->left));
    return data;
  }
  p = *root;
  data = p->data;
  *root = p->right;
  xfree(p);
  return data;
}

int cmp1(char *a, char *b) {
  return strcmp(a, b);
}

int cmp2(char *a, char *b) {
  return -strcmp(a, b);
}

void task_sort(FILE *fp) {
  struct node *root;
  char *p;
  root = NULL;
  while ((p = mygetline(fp))) {
    if (flagS)
      push(&root, p, (int (*)(void *, void *))cmp1);
    else
      push(&root, p, (int (*)(void *, void *))cmp2);
  }
  while ((p = pop(&root))) {
    printf("%s\n", p);
    xfree(p);
  }
}

void usage(char *cmd) {
  fprintf(stderr, "usage: %s <flag:> <file>\n", cmd);
  fprintf(stderr, "       flag: 0:descending order\n");
  fprintf(stderr, "             1:ascending order\n");
}

int main(int argc, char *argv[]) {
  FILE *fp;
  if (argc != 3) {
    usage(argv[0]);
    exit(-1);
  }
  if (*argv[1] == '1')
    flagS = 1;
  
  if ((fp = fopen(argv[2], "r")) == NULL) {
    fprintf(stderr, "cannot open the file '%s', aborted\n", argv[2]);
    usage(argv[0]);
    exit(-1);
  }
  task_sort(fp);
  fclose(fp);
/*  xmallocdump(); */
  return 0;
}
/* end */

usage: /t <flag:> <file>
       flag: 0:descending order
             1:ascending order

Exited: ExitFailure 255