(gawk.info) Arithmetic Ops
Conversion of Strings and Numbers
Strings are converted to numbers, and numbers 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 this:
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, and 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 are converted to zero.
The exact manner in which numbers are converted into strings is
controlled by the `awk' built-in variable `CONVFMT' ( Built-in
Variables). Numbers are converted using the `sprintf' function
( Built-in Functions for String Manipulation String Functions.)
with `CONVFMT' as the format specifier.
`CONVFMT''s default value is `"%.6g"', which prints a value with at
least six significant digits. For some applications you will want to
change it to specify more precision. On most modern machines, you must
print 17 digits to capture a floating point number's value exactly.
Strange results can happen 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, all numbers
will be converted 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' specified that the value of
`OFMT' was used 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 will not change their behavior. However, this use of `OFMT'
is something to keep in mind if you must port your program to other
implementations of `awk'; we recommend that instead of changing your
programs, you just port `gawk' itself! The `print' Statement
Print, for more information on the `print' statement.
(gawk.info) Arithmetic Ops
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