File: gawk.info,  Node: Numeric Array Subscripts,  Next: Uninitialized Subscripts,  Prev: Array Basics,  Up: Arrays

8.2 Using Numbers to Subscript Arrays
=====================================

An important aspect to remember about arrays is that _array subscripts
are always strings_.  When a numeric value is used as a subscript, it is
converted to a string value before being used for subscripting (*note
Conversion::).  This means that the value of the predefined variable
'CONVFMT' can affect how your program accesses elements of an array.
For example:

     xyz = 12.153
     data[xyz] = 1
     CONVFMT = "%2.2f"
     if (xyz in data)
         printf "%s is in data\n", xyz
     else
         printf "%s is not in data\n", xyz

This prints '12.15 is not in data'.  The first statement gives 'xyz' a
numeric value.  Assigning to 'data[xyz]' subscripts 'data' with the
string value '"12.153"' (using the default conversion value of
'CONVFMT', '"%.6g"').  Thus, the array element 'data["12.153"]' is
assigned the value one.  The program then changes the value of
'CONVFMT'.  The test '(xyz in data)' generates a new string value from
'xyz'--this time '"12.15"'--because the value of 'CONVFMT' only allows
two significant digits.  This test fails, because '"12.15"' is different
from '"12.153"'.

   According to the rules for conversions (*note Conversion::), integer
values always convert to strings as integers, no matter what the value
of 'CONVFMT' may happen to be.  So the usual case of the following
works:

     for (i = 1; i <= maxsub; i++)
         do something with array[i]

   The "integer values always convert to strings as integers" rule has
an additional consequence for array indexing.  Octal and hexadecimal
constants (*note Nondecimal-numbers::) are converted internally into
numbers, and their original form is forgotten.  This means, for example,
that 'array[17]', 'array[021]', and 'array[0x11]' all refer to the same
element!

   As with many things in 'awk', the majority of the time things work as
you would expect them to.  But it is useful to have a precise knowledge
of the actual rules, as they can sometimes have a subtle effect on your
programs.