Text editor capable of viewing invisibles?

Question

A recent problem* left me wondering whether there is a text editor out there that lets you see every single character of the file, even if they are invisible? Specifically,

Answer 1

Open the file in EMACS and do a M-X hexl-mode. You'll get a display that looks like this:

87654321  0011 2233 4455 6677 8899 aabb ccdd eeff  0123456789abcdef                               
00000000: 2320 2020 2020 2020 2020 2020 2020 2020  #               
00000010: 2020 2020 2020 2020 2020 2020 2020 2020                  
00000020: 2020 2020 2020 2020 2020 2020 2020 2020                  
00000030: 2d2a 2d20 4175 746f 636f 6e66 202d 2a2d  -*- Autoconf -*-
00000040: 0a23 2050 726f 6365 7373 2074 6869 7320  .# Process this 
00000050: 6669 6c65 2077 6974 6820 6175 746f 636f  file with autoco
00000060: 6e66 2074 6f20 7072 6f64 7563 6520 6120  nf to produce a 
00000070: 636f 6e66 6967 7572 6520 7363 7269 7074  configure script
00000080: 2e0a 2320 4f72 6465 7220 6973 206c 6172  ..# Order is lar
00000090: 6765 6c79 2069 7272 6576 656c 6c61 6e74  gely irrevellant
000000a0: 2c20 616c 7468 6f75 6768 2069 7420 6d75  , although it mu
000000b0: 7374 2073 7461 7274 2077 6974 6820 4143  st start with AC
000000c0: 5f49 4e49 5420 616e 6420 656e 6420 7769  _INIT and end wi
000000d0: 7468 2041 435f 4f55 5450 5554 0a23 2053  th AC_OUTPUT.# S
000000e0: 6565 2068 7474 703a 2f2f 6175 746f 746f  ee http://autoto
000000f0: 6f6c 7365 742e 736f 7572 6365 666f 7267  olset.sourceforg
00000100: 652e 6e65 742f 7475 746f 7269 616c 2e68  e.net/tutorial.h

Answer 2

Notepad++ rocks:

Answer 3

You can also user Notepad ++ to show them. Here is an example, the black boxes are control characters.