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The C Programming Language, 2nd Edition, by Kernighan and Ritchie
Exercise 7.02 on page 155

Write a program that will print arbitrary input in a sensible way. As a minimum, it should print non-graphic characters in octal or hexadecimal according to local custom, and break long text lines.

Solution by Richard Heathfield

/* Use -o for octal output, -x for hexadecimal
 */

#include <stdio.h>

#define OCTAL        8
#define HEXADECIMAL 16


void ProcessArgs(int argc, char *argv[], int *output)
{
  int i = 0;
  while(argc > 1)
  {
    --argc;
    if(argv[argc][0] == '-')
    {
      i = 1;
      while(argv[argc][i] != '\0')
      {
        if(argv[argc][i] == 'o')
        {
          *output = OCTAL;
        }
        else if(argv[argc][i] == 'x')
        {
          *output = HEXADECIMAL;
        }
        else
        {
          /* Quietly ignore unknown switches, because we don't want to
           * interfere with the program's output. Later on in the
           * chapter, the delights of fprintf(stderr, "yadayadayada\n")
           * are revealed, just too late for this exercise.
           */
        }
      ++i;
      }
    }
  }
}

int can_print(int ch)
{
  char *printable = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890 !\"#%&'()*+,-./:;<=>?[\\]^_{|}~\t\f\v\r\n";

  char *s;
  int found = 0;

  for(s = printable; !found && *s; s++)
  {
    if(*s == ch)
    {
      found = 1;
    }
  }

  return found;
}

int main(int argc, char *argv[])
{
  int split = 80;
  int output = HEXADECIMAL;
  int ch;
  int textrun = 0;
  int binaryrun = 0;
  char *format;
  int width = 0;

  ProcessArgs(argc, argv, &output);

  if(output == HEXADECIMAL)
  {
    format = "%02X ";
    width = 4;
  }
  else
  {
    format = "%3o ";
    width = 4;
  }

  while((ch = getchar()) != EOF)
  {
    if(can_print(ch))
    {
      if(binaryrun > 0)
      {
        putchar('\n');
        binaryrun = 0;
        textrun = 0;
      }
      putchar(ch);
      ++textrun;
      if(ch == '\n')
      {
        textrun = 0;
      }

      if(textrun == split)
      {
        putchar('\n');
        textrun = 0;
      }
    }
    else
    {
      if(textrun > 0 || binaryrun + width >= split)
      {
        printf("\nBinary stream: ");
        textrun = 0;
        binaryrun = 15;
      }
      printf(format, ch);
      binaryrun += width;
    }
  }

  putchar('\n');

  return 0;
}