This tip shows how to convert numbers from hexadecimal to decimal, and the reverse. A variety of methods are given, including some simple commands you can enter, and some scripts to easily replace hex numbers with decimal, or to replace decimal with hex. Handling percent-encoded text is also discussed, and there are links to tips showing how to edit a binary file in hex.

Commands

Occasional conversions can be performed by entering commands. In Vim, put the cursor on 0x12345 and type :echo then Space Ctrl-R Ctrl-W Enter. That will execute :echo 0x12345 which displays 74565 (decimal equivalent of hex 12345).

An example of converting decimal to hex would be to enter :echo printf('%x',74565) which displays 12345 (hex equivalent of decimal 74565).

In addition, the expression register can be used to enter converted numbers while typing. In insert mode, press Ctrl-R then = then the expression wanted, then press Enter. The value of the expression is inserted, and you will remain in insert mode. For example, <C-R>=0x09ab<Enter> will insert 2475, and <C-R>=printf('0x%04x',2475)<Enter> will insert 0x09ab.

In normal mode, type ga to display the decimal and hex values for the character under the cursor, or type g8 to display the hex bytes for a UTF-8 character.

The following commands illustrate other simple techniques to convert strings to numbers which are displayed in decimal (the :echo is just for illustration; these techniques would be used in a script). The first shows that adding zero to a string converts the string to a number.

The following convert decimal numbers to hex strings.

Copying a hex number as decimal

With the following mapping, you can put the cursor on a hex number and press \h (assuming the default backslash leader) to yank the value of the hex number (using :let means the equivalent decimal string is copied). You can then move the cursor elsewhere and press p to paste the decimal value.

nnoremap \h :let @@=<C-R><C-W><CR>

Alternatively, you can use a global variable to avoid using a register. With these mappings, \h will yank a hex value, and \p will paste the decimal string:

nnoremap \h :let Value=<C-R><C-W><CR>
nnoremap \p :if exists('Value')<Bar>normal i<C-R>=Value<CR><Esc><Bar>:endif<CR>

User commands

Put the following in your vimrc to define user commands to convert between hex and decimal. You can convert a number entered on the command line, or all numbers in selected text.

command! -nargs=? -range Dec2hex call s:Dec2hex(<line1>, <line2>, '<args>')
function! s:Dec2hex(line1, line2, arg) range
  if empty(a:arg)
    if histget(':', -1) =~# "^'<,'>" && visualmode() !=# 'V'
      let cmd = 's/\%V\<\d\+\>/\=printf("0x%x",submatch(0)+0)/g'
    else
      let cmd = 's/\<\d\+\>/\=printf("0x%x",submatch(0)+0)/g'
    endif
    try
      execute a:line1 . ',' . a:line2 . cmd
    catch
      echo 'Error: No decimal number found'
    endtry
  else
    echo printf('%x', a:arg + 0)
  endif
endfunction

command! -nargs=? -range Hex2dec call s:Hex2dec(<line1>, <line2>, '<args>')
function! s:Hex2dec(line1, line2, arg) range
  if empty(a:arg)
    if histget(':', -1) =~# "^'<,'>" && visualmode() !=# 'V'
      let cmd = 's/\%V0x\x\+/\=submatch(0)+0/g'
    else
      let cmd = 's/0x\x\+/\=submatch(0)+0/g'
    endif
    try
      execute a:line1 . ',' . a:line2 . cmd
    catch
      echo 'Error: No hex number starting "0x" found'
    endtry
  else
    echo (a:arg =~? '^0x') ? a:arg + 0 : ('0x'.a:arg) + 0
  endif
endfunction

The above defines user commands :Dec2hex and :Hex2dec that will either display the result of converting a number that you enter, or will convert all numbers in selected text. A decimal number is a word consisting only of decimal digits, while a hex number consists of "0x" followed by one or more hex digits.

If no argument is entered with these commands, a range may be specified. The default range is the current line. A visual selection (character, line, or block) can also specify a range. When using a visual block (selection starts with Ctrl-V, or Ctrl-Q if Ctrl-V is used for paste), only numbers inside the block are converted. Example commands:

Converting strings

Following are some methods for working with percent-encoded text, and for showing ASCII characters in hex.

" Convert current line to percent-encoded hex for disallowed punctuation.
" Example: line "A/C[123]D\E" is converted to "A%2FC%5B123%5DD%5CE".
nnoremap <Leader>h :s@\([;(){}\[\]+ ,\-><\|=%&^\\/"']\)@\='%'.printf('%02X',char2nr(submatch(1)))@g<CR>
" Convert percent-encoded hex in current line to text (reverse of above).
nnoremap <Leader>H :s@%\(\x\x\)@\=nr2char('0x'.submatch(1))@g<CR>

" Convert each ASCII character in a string to hex bytes.
" Example: ":Str2hex ABC 123" displays "41 42 43 20 31 32 33".
command! -nargs=* Str2hex echo Str2hex(<q-args>)
function! Str2hex(arg)
  return join(map(split(a:arg, '\zs'), 'printf("%02x", char2nr(v:val))'))
endfunction

General functions

A script could use the following functions for conversions between decimal and hex.

" Return hex string equivalent to given decimal string or number.
function! Dec2hex(arg)
  return printf('%x', a:arg + 0)
endfunction

" Return number equivalent to given hex string ('0x' is optional).
function! Hex2dec(arg)
  return (a:arg =~? '^0x') ? a:arg + 0 : ('0x'.a:arg) + 0
endfunction

Sometimes one just needs to know the value of decimal/hexadecimal value, without changing the text. Put the following in your vimrc to define user command 'gn' to print the number under the cursor converted to hex/decimal (similar to built-in command 'ga' and 'g8' for ASCII character under the cursor):

nnoremap gn :call DecAndHex(expand("<cWORD>"))<CR>

function! DecAndHex(number)
  let ns = '[.,;:''"<>()^_lL]'      " number separators
  if a:number =~? '^' . ns. '*[-+]\?\d\+' . ns . '*$'
     let dec = substitute(a:number, '[^0-9+-]*\([+-]\?\d\+\).*','\1','')
     echo dec . printf('  ->  0x%X, -(0x%X)', dec, -dec)
  elseif a:number =~? '^' . ns. '*\%\(h''\|0x\|#\)\?\(\x\+\)' . ns . '*$'
     let hex = substitute(a:number, '.\{-}\%\(h''\|0x\|#\)\?\(\x\+\).*','\1','')
     echon '0x' . hex . printf('  ->  %d', eval('0x'.hex))
     if strpart(hex, 0,1) =~? '[89a-f]' && strlen(hex) =~? '2\|4\|6'
        " for 8/16/24 bits numbers print the equivalent negative number
        echon ' ('. float2nr(eval('0x'. hex) - pow(2,4*strlen(hex))) . ')'
     endif
     echo
  else
     echo "NaN"
  endif
endfunction

Numbers containing character A-F or prefixed with '0x', 'h' or '#' are treated as hexadecimal values:

Using external programs

 TO DO 

• Fix or delete this section.
• The following is from old tip 772. It does not seem helpful, but we should discuss the menus somewhere so I am keeping the text for a while.

This example creates a menu for conversions using the bc calculator which is a standard utility on many Unix-based systems. Visually select the number (without leading '0x'), right click the selection, and select from the popup menu to transform the number.

vmenu 1.220 PopUp.&nr2hex <Esc>:exec("!echo \\"obase=16;".@*."\\" \| bc -l -q ")<CR>
vmenu 1.220 PopUp.hex&2nr <Esc>:exec("!echo \\"ibase=16;".toupper(@*)."\\" \| bc -l -q ")<CR>

More is needed to make it work. I had to do the following on a Linux system, but I suspect a setting regarding register * is also being used (it assumes that the selected text is in the * register).

set mousemodel=popup
vmenu 1.220 PopUp.&nr2hex <Esc>:exec '!echo "obase=16;'.@*.'" \| bc -l -q '<CR>
vmenu 1.220 PopUp.hex&2nr <Esc>:exec '!echo "ibase=16;'.toupper(@*).'" \| bc -l -q '<CR>

See also

• Hex dump editing or displaying binary files in hex
• Improved hex editing automating some of the procedures to edit binary files in hex
• ConvertBase plugin to convert to/from various numeric bases
• Convert Hexadecimal to Decimal Number online tool to convert hex to dec
• From one to another number system, article related to creating computer program for conversion of number from one to another number system with source code written in C#

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