The strtonum() function (see 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, n, i, k, c)
{
if (str ~ /^0[0-7]*$/) {
# octal
n = length(str)
ret = 0
for (i = 1; i <= n; i++) {
c = substr(str, i, 1)
# index() returns 0 if c not in string,
# includes c == "0"
k = index("1234567", c)
ret = ret * 8 + k
}
} else if (str ~ /^0[xX][[:xdigit:]]+$/) {
# 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)
# index() returns 0 if c not in string,
# includes c == "0"
k = index("123456789abcdef", c)
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[8] = "1.32E2"
#
# for (i = 1; i in a; i++)
# print a[i], strtonum(a[i]), mystrtonum(a[i])
# }
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 "1234567" of the current
octal digit.
The return value will either be the same number as the digit, or zero
if the character is not there, which will be true for a ‘0’.
This is safe, because the regexp test in the if ensures that
only octal values are converted.
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.