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(gawk.info)Non-decimal-numbers

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Octal and Hexadecimal Numbers
-----------------------------

   In `awk', all numbers are in decimal; i.e., base 10.  Many other
programming languages allow you to specify numbers in other bases, often
octal (base 8) and hexadecimal (base 16).  In octal, the numbers go 0,
1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc..  Just as `11' in decimal is 1
times 10 plus 1, so `11' in octal is 1 times 8, plus 1. This equals
nine in decimal.  In hexadecimal, there are 16 digits. Since the
everyday decimal number system only has ten digits (`0'--`9'), the
letters `a' through `f' are used to represent the rest.  (Case in the
letters is usually irrelevant; hexadecimal `a' and `A' have the same
value.)  Thus, `11' in hexadecimal is 1 times 16 plus 1, which equals
17 in decimal.

   Just by looking at plain `11', you can't tell what base it's in.
So, in C, C++, and other languages derived from C, there is a special
notation to help signify the base.  Octal numbers start with a leading
`0', and hexadecimal numbers start with a leading `0x' or `0X':

`11'
     Decimal 11.

`011'
     Octal 11, decimal value 9.

`0x11'
     Hexadecimal 11, decimal value 17.

   This example shows the difference:

     $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }'
     -| 9, 11, 17

   Being able to use octal and hexadecimal constants in your programs
is most useful when working with data that cannot be represented
conveniently as characters or as regular numbers, such as binary data
of various sorts.

   `gawk' allows the use of octal and hexadecimal constants in your
program text.  However, such numbers in the input data are not treated
differently; doing so by default would break old programs.  (If you
really need to do this, use the `--non-decimal-data' command-line
option, Note: Allowing Non-Decimal Input Data..)  If
you have octal or hexadecimal data, you can use the `strtonum' function
(Note: String Manipulation Functions.)  to convert
the data into a number.  Most of the time, you will want to use octal
or hexadecimal constants when working with the built-in bit
manipulation functions; see Note: Using `gawk''s Bit Manipulation
Functions, for more information.

   Unlike some early C implementations, `8' and `9' are not valid in
octal constants; e.g., `gawk' treats `018' as decimal 18.

     $ gawk 'BEGIN { print "021 is", 021 ; print 018 }'
     -| 021 is 17
     -| 18

   Octal and hexadecimal source code constants are a `gawk' extension.
If `gawk' is in compatibility mode (*note Command-Line Options:
Options.), they are not available.

Advanced Notes: A Constant's Base Does Not Affect Its Value
-----------------------------------------------------------

   Once a numeric constant has been converted internally into a number,
`gawk' no longer remembers what the original form of the constant was;
the internal value is always used.  This has particular consequences
for conversion of numbers to strings:

     $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }'
     -| 0x11 is <17>