Node:Conversion, Next:Arithmetic Ops, Previous:Variables, Up:Expressions
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 4 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 (see Built-in Variables).
Numbers are converted using the sprintf function
with CONVFMT as the format
specifier
(see String Manipulation 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.
See The print Statement,
for more information on the print statement.
Pathological cases can require up to 752 digits (!), but we doubt that you need to worry about this.