Strtonum Function (The GNU Awk User’s Guide)
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10.2.1 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, 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.
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