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Honestly, I have no idea. But I guess it could have something to do with the fact that the maximum value for a signed integer with only one byte is +/- 7 (0111 = +7, 1111 = -7 … if I remember binary correctly).

By starting the number with a leading zero, when Ruby typecasts the string to an integer, it is doing so as an octal. 08 is not a valid octal number, hence the error.

http://en.wikipedia.org/wiki/Octal

Ernie, thanks for that. Next (obvious) question is why? Wouldn’t decimal have been a more sensible choice?

It’s not Ruby-specific. A lot of dynamically typed interpreted languages allow for alternate representations of integers for convenience. Common shorthand for octal is a leading zero, while hexadecimal can be done with a preceding “0x”.

Using 0x for hex makes some sense and using something similar for Octal would also make sense. But to not default to decimal just seems daft to me. As a programmer, how many times have you converted a string to an integer and wanted it treated as octal, rather than decimal?

Hey David,

how many times does a programmer have a string like “08” that he needs to convert to an integer to format it?

Apparently String#% does an Integer(“08”) internally which is a little more restrictive about valid integer values than String#to_i is.
However a simple “%02d” % “08”.to_i works if you really need it.

The original printf format strings however expect a decimal value if you supply a %d and as Ruby is a dynamic language,
it would make sense to handle “08” as an actual decimal in that case.

If you find some time, it would be interesting to see this on the Ruby mailing list.

Cheers

Pascal

David,

But that’s just it—you didn’t convert it to an integer when you passed it as an argument, you told sprintf to do that for you. Using String#to_i was the solution if you wanted to manage the conversion yourself. The “0x” and “0” for hexadecimal and octal integer representations have been around for ages, it’s just one of those things to get used to, as it’s nearly universal across programming languages, and you’re certainly not the first to get bitten by it.

As Pascal pointed out, String#to_i behaves differently than a straight Integer cast does. This is because String#to_i takes an optional base parameter, defaulting to 10, and has additional logic to support varying bases.

I disagree with Pascal that it makes sense to handle the assume the argument for the %d conversion is a decimal number on the right hand side, though—a big portion of what sprintf is designed to do is do on-the-fly format conversions of an integer to different string representations. Because of this, it’s a perfectly valid expectation to pass in an Integer in octal format and request it in decimal in the output. The best policy is always to pass the value in as an Integer, not as a string, to avoid any ambiguity.