static char *usage = "usage: %s <N> <filename>\n";

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

/* #define DEBUG */
#if defined(DEBUG)
#include "xmalloc.h"
#else
#define xmalloc(x, y) malloc(x)
#define xfree(x, y) free(x)
#define xrealloc(x, y, z) realloc((x), (y))
#define xmallocdump()
#endif
#define GETLINE 1001
#define IDARRAY 1002
#define IDNAME  1003

#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, GETLINE)) == 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,
                           GETLINE)) == NULL) {
      xfree(outbuff_malloc, GETLINE);
      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, GETLINE);
  return NULL;
}

void task_console2file(int n, char *filename) {
  FILE *fp;
  int i;
  if ((fp = fopen(filename, "w")) == NULL)
    return;
  for (i = 0; i < n; i++) {
    int no;
    char *p;
    do {
      printf("No: ");
    } while ((p = mygetline(stdin)) == NULL);
    no = atoi(p);
    xfree(p, GETLINE);
    do {
      printf("Name: ");
    } while ((p = mygetline(stdin)) == NULL);
    fprintf(fp, "%d, %s\n", no, p);
    xfree(p, GETLINE);
  }
  fclose(fp);
}

struct stu {
  int num;
  char *name;
};

int cmp(struct stu *a, struct stu *b) {
  return a->num > b->num;
}

void task_readfile_sort(int n, char *filename) {
  FILE *fp;
  struct stu *a;
  int i, max;
  if ((fp = fopen(filename, "r")) == NULL)
    return;
  if ((a = xmalloc(sizeof(struct stu) * n, IDARRAY)) == NULL)
    return;
  for (i = 0; i < n; i++) {
    char *p, *q;
    if ((p = mygetline(fp)) == NULL)
      break;
    for (q = p; *q != ','; q++)
      ;
    *q = '\0';
    q++;
    a[i].num = atoi(p);
    if ((a[i].name = xmalloc(strlen(q) + 1, IDNAME)) == NULL) {
      xfree(p, GETLINE);
      break;
    }    
    strcpy(a[i].name, q);
    xfree(p, GETLINE);
  }
  fclose(fp);
  max = i;
  qsort(a, max, sizeof(a[0]), (int (*)(const void *, const void *))cmp);
  for (i = 0; i < max; i++)
    printf("%d: %s\n", a[i].num, a[i].name);

  for (i = 0; i < max; i++)
    xfree(a[i].name, IDNAME);
  xfree(a, IDARRAY);
}

int main(int argc, char *argv[]) {
  FILE *fp;
  int n;
  if (argc != 3) {
    fprintf(stderr, usage, argv[0]);
    exit(-1);
  }
  n = atoi(argv[1]);
  if (n <= 0) {
    fprintf(stderr, "n must be > 0\n");
    fprintf(stderr, usage, argv[0]);
    exit(-1);
  }
  if ((fp = fopen(argv[2], "w")) == NULL) {
    fprintf(stderr, "cannot open the file: %s\n", argv[2]);
    fprintf(stderr, usage, argv[0]);
    exit(-1);
  }    
  fclose(fp);

  task_console2file(n, argv[2]);
  task_readfile_sort(n, argv[2]);
  xmallocdump();
  return 0;
}
/* end */

usage: /t <N> <filename>

Exited: ExitFailure 255