(gawk.info)Numeric Array Subscripts

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

   An important aspect of arrays to remember is that *array subscripts
are always strings*.  If you use a numeric value as a subscript, it
will be converted to a string value before it is used for subscripting
(Note: Conversion of Strings and Numbers.).

   This means that the value of the built-in variable `CONVFMT' can
potentially 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"'), and assigns one to `data["12.153"]'.  The program
then changes the value of `CONVFMT'.  The test `(xyz in data)'
generates a new string value from `xyz', this time `"12.15"', since the
value of `CONVFMT' only allows two significant digits.  This test fails,
since `"12.15"' is a different string from `"12.153"'.

   According to the rules for conversions (Note: Conversion of Strings
and Numbers.), integer values are always converted to
strings as integers, no matter what the value of `CONVFMT' may happen
to be.  So the usual case of:

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

will work, no matter what the value of `CONVFMT'.

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