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(gawk.info)Conversion

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Conversion of Strings and Numbers
=================================

   Strings are converted to numbers and numbers are converted to
strings, if the context of the `awk' program demands it.  For example,
if the value of either `foo' or `bar' in the expression `foo + bar'
happens to be a string, it is converted to a number before the addition
is performed.  If numeric values appear in string concatenation, they
are converted to strings.  Consider the following:

     two = 2; three = 3
     print (two three) + 4

This prints the (numeric) value 27.  The numeric values of the
variables `two' and `three' are converted to strings and concatenated
together.  The resulting string is converted back to the number 23, to
which four is then added.

   If, for some reason, you need to force a number to be converted to a
string, concatenate the empty string, `""', with that number.  To force
a string to be converted to a number, add zero to that string.  A
string is converted to a number by interpreting any numeric prefix of
the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to
1000, and `"25fix"' has a numeric value of 25.  Strings that can't be
interpreted as valid numbers convert to zero.

   The exact manner in which numbers are converted into strings is
controlled by the `awk' built-in variable `CONVFMT' (Note: Built-in
Variables).  Numbers are converted using the `sprintf' function with
`CONVFMT' as the format specifier (*note String Manipulation Functions:
String Functions.).

   `CONVFMT''s default value is `"%.6g"', which prints a value with at
least six significant digits.  For some applications, you might want to
change it to specify more precision.  On most modern machines, 17
digits is enough to capture a floating-point number's value exactly,
most of the time.(1)

   Strange results can occur if you set `CONVFMT' to a string that
doesn't tell `sprintf' how to format floating-point numbers in a useful
way.  For example, if you forget the `%' in the format, `awk' converts
all numbers to the same constant string.  As a special case, if a
number is an integer, then the result of converting it to a string is
_always_ an integer, no matter what the value of `CONVFMT' may be.
Given the following code fragment:

     CONVFMT = "%2.2f"
     a = 12
     b = a ""

`b' has the value `"12"', not `"12.00"'.  (d.c.)

   Prior to the POSIX standard, `awk' used the value of `OFMT' for
converting numbers to strings.  `OFMT' specifies the output format to
use when printing numbers with `print'.  `CONVFMT' was introduced in
order to separate the semantics of conversion from the semantics of
printing.  Both `CONVFMT' and `OFMT' have the same default value:
`"%.6g"'.  In the vast majority of cases, old `awk' programs do not
change their behavior.  However, these semantics for `OFMT' are
something to keep in mind if you must port your new style program to
older implementations of `awk'.  We recommend that instead of changing
your programs, just port `gawk' itself.  *Note The `print' Statement:
Print, for more information on the `print' statement.

   ---------- Footnotes ----------

   (1) Pathological cases can require up to 752 digits (!), but we
doubt that you need to worry about this.