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12.2.1 Converting Strings To Numbers
The strtonum() function (see section String-Manipulation Functions)
is a gawk extension. The following function
provides an implementation for other versions of awk:
# mystrtonum --- convert string to number
function mystrtonum(str, ret, chars, n, i, k, c)
{
if (str ~ /^0[0-7]*$/) {
# octal
n = length(str)
ret = 0
for (i = 1; i <= n; i++) {
c = substr(str, i, 1)
if ((k = index("01234567", c)) > 0)
k-- # adjust for 1-basing in awk
ret = ret * 8 + k
}
} else if (str ~ /^0[xX][[:xdigit:]]+/) {
# hexadecimal
str = substr(str, 3) # lop off leading 0x
n = length(str)
ret = 0
for (i = 1; i <= n; i++) {
c = substr(str, i, 1)
c = tolower(c)
if ((k = index("0123456789", c)) > 0)
k-- # adjust for 1-basing in awk
else if ((k = index("abcdef", c)) > 0)
k += 9
ret = ret * 16 + k
}
} else if (str ~ \
/^[-+]?([0-9]+([.][0-9]*([Ee][0-9]+)?)?|([.][0-9]+([Ee][-+]?[0-9]+)?))$/) {
# decimal number, possibly floating point
ret = str + 0
} else
ret = "NOT-A-NUMBER"
return ret
}
# BEGIN { # gawk test harness
# a[1] = "25"
# a[2] = ".31"
# a[3] = "0123"
# a[4] = "0xdeadBEEF"
# a[5] = "123.45"
# a[6] = "1.e3"
# a[7] = "1.32"
# a[7] = "1.32E2"
#
# for (i = 1; i in a; i++)
# print a[i], strtonum(a[i]), mystrtonum(a[i])
# }
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The function first looks for C-style octal numbers (base 8).
If the input string matches a regular expression describing octal
numbers, then mystrtonum() loops through each character in the
string. It sets k to the index in "01234567" of the current
octal digit. Since the return value is one-based, the ‘k--’
adjusts k so it can be used in computing the return value.
Similar logic applies to the code that checks for and converts a
hexadecimal value, which starts with ‘0x’ or ‘0X’.
The use of tolower() simplifies the computation for finding
the correct numeric value for each hexadecimal digit.
Finally, if the string matches the (rather complicated) regexp for a
regular decimal integer or floating-point number, the computation
‘ret = str + 0’ lets awk convert the value to a
number.
A commented-out test program is included, so that the function can
be tested with gawk and the results compared to the built-in
strtonum() function.
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