基本情報技術者試験 ファイルの内容を16進数で表示する

令和元年度秋期の基本情報技術者試験の午後問題の問９の「ファイルの内容を16進数で表示する」プログラムを実行しました。

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

#define WIDTH 60
#define MASKCHR '.'

void dump(char *filename, long from, long to) {
  FILE *infile;
  int chr, pos = 0;
  long cnt = 0;
  char tbl_char[256], buf_char[WIDTH + 1];
  char tbl_high[256], buf_high[WIDTH + 1];
  char tbl_low[256], buf_low[WIDTH + 1];
  char hex[] = "0123456789ABCDEF";

  for (chr = 0x00; chr <= 0xFF; chr++) {
    if ((0x20 <= chr) && (chr <= 0x7E))
      tbl_char[chr] = chr;
    else
      tbl_char[chr] = MASKCHR;
    tbl_high[chr] = hex[chr >> 4];
    tbl_low[chr] = hex[chr & 0x0F];
  }

  buf_char[WIDTH] = buf_high[WIDTH] = buf_low[WIDTH] = '\0';
  infile = fopen(filename, "rb");
  while ( ((chr = fgetc(infile)) != EOF) && ((to < 0) || (cnt <= to)) ) {
    cnt++;
    if (cnt > from) {
      buf_char[pos] = tbl_char[chr];
      buf_high[pos] = tbl_high[chr];
      buf_low[pos] = tbl_low[chr];
      pos++;
      if (pos == WIDTH) {
        printf("%10ld  %s\n%12s%s\n%12s%s\n\n",
               cnt - WIDTH, buf_char, " ", buf_high, " ", buf_low);
        pos = 0;
      }
    }
  }
  if (pos > 0) {
    buf_char[pos] = buf_high[pos] = buf_low[pos] = '\0';
    printf("%10ld  %s\n%12s%s\n%12s%s\n\n",
           cnt - pos, buf_char, " ", buf_high, " ", buf_low);
  }
  if (chr == EOF)
    printf("END OF DATA ... %ld byte(s)\n", cnt - from);
  else
    printf("END OF DUMP ... %ld byte(s)\n", cnt - from);

  fclose(infile);
}

int main(int argc, char *argv[]) {
  dump(argv[1], atol(argv[2]), atol(argv[3]));

  return 0;
}

$ cat ascii.txt 
 !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~

$ od -tx1 ascii.txt 
000000 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f
000010 30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f
000020 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f
000030 50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f
000040 60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f
000050 70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 0a
000060

$ ./hexdump ascii.txt 0 -1
         0   !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[
            222222222222222233333333333333334444444444444444555555555555
            0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789AB

        60  \]^_`abcdefghijklmnopqrstuvwxyz{|}~.
            555566666666666666667777777777777770
            CDEF0123456789ABCDEF0123456789ABCDEA

END OF DATA ... 96 byte(s)