Write a program that prompts the user for an input file name, opens the file as

Question

Write a program that prompts the user for an input file name, opens the file as binary read-mode, and displays the first 256 bytes of the input file on the screen, as hex and their ASCII equivalent. Display 16 bytes per line, separated by a space, and then the ASCII for the same 16 bytes, to the right, no spaces. Try your program on a text file and a binary Bitmap file (and maybe an XLS file also). Example session screen shot below. Hint: to display a byte as hex, use printf("%3hhX", (unsigned char)mybyte); and to display a byte as a char, use printf("%c", (unsigned char)mybyte

Explanation / Answer

*   fhdump.prg

parameters   filename, start, stop, dwidth
private   talking, hex_ascii, d_len, di, str16, d_str, hex_str

if set("talk") = "ON"
      set talk OFF
      talking = .T.
else
      talking = .F.
endif
crlf = chr(13) + chr(10)           && for convenience
hex_ascii = ""               && buffer for output line
dwidth = min(dwidth, 200)           && largest reasonable display width
dwidth = max(dwidth, 1)           && smallest reasonable display width
fh = fopen(filename)               && open file at low level
if fh > 0                   && proceed only if valid handle
      ?                   && begin new line
      xi = fseek(fh, start)           && skip to desired offset in file
      do while !feof(fh) AND xi <= stop   && stop at end of file
          raw = fread(fh, dwidth)   && read a block of desired size
          hex_str = padr(hex(raw, " "), dwidth * 3)   && pad short line
          hex_ascii = str(xi, 5) +": "+ hex_str +"| "+ strip(raw) + crlf
          ?? hex_ascii           && offset: hex digits | stripped ASCII
          xi = xi + dwidth       && bump the offset
      enddo
endif
fh = fclose(fh)               && housekeeping

if talking
      set talk ON
endif

return

* most output devices don't deal well with control characters, so ...
function strip               && replace control chars in string with '.'
      parameters   rawstring
      private   outstring, sx, byte
      outstring = ""
      for sx = 1 to len(rawstring)       && examine each byte in string
          byte = substr(rawstring, sx, 1)   && get single byte
          outstring = outstring + iif(asc(byte) > 31, byte, ".")
      endfor               && keep printables, convert controls
return outstring

* convert a string of bytes to hex, padded with 'padchar'
function hex
      parameters   string, padchr       && bytes and separator
      private   nbytes, hex_str, ix, bc
      padchr = iif(type("padchr") = "C", padchr, "")   && optional separator
      hex_str = ""               && result buffer
      nbytes = len(string)           && count the bytes
      for ix = 1 to nbytes           && and one by one ...
          bc = substr(string, ix, 1)   && extract a byte
          hex_str = hex_str + hdigits(bc) + iif(ix = nbytes, "", padchr)
      endfor               && and build result hex digit string
return hex_str

* render a byte as a pair of hex digits
function hdigits
      parameters   char
      private   ch_hi, ch_lo, av, nib
      av = asc(char)           && ASCII value of byte
      nib = int(av / 16)           && high order nibble
      ch_hi = chr(nib + iif(nib > 9, 55, 48))   && hex nibble
      nib = mod(av, 16)           && low order nibble
      ch_lo = chr(nib + iif(nib > 9, 55, 48))   && hex nibble
return ch_hi + ch_lo               && two nibbles to a byte

eof

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