On 12-04-24 10:33 PM, Simon Urbanek wrote:
On Apr 24, 2012, at 9:12 PM, Duncan Murdoch wrote:
On 12-04-24 5:12 PM, Simon Urbanek wrote:
On Apr 24, 2012, at 4:24 PM, Joran Elias wrote:
I stumbled across this by accident from this StackOverflow question:
http://stackoverflow.com/q/10300325/324364
and a subsequent discussion in the StackOverflow R chat room:
http://chat.stackoverflow.com/transcript/message/3431991#3431991
The issue is the output from the following code:
sprintf('%05s',as.character(1:5))
It appears that when this is run in OS X in either 2.14.2 or 2.15.0, the
output is:
[1] "00001" "00002" "00003" "00004" "00005"
whereas when it is run on other platforms (I saw examples from various
Windows versions and one user on Ubuntu, all using 2.15.0 I believe) you
get:
[1] " 1" " 2" " 3" " 4" " 5"
There was some uncertainty as to which behavior is "expected".
The behavior of "%0s" is undefined -- this is documented both by R and POSIX
(arguably more clearly in the latter), so any behavior should be expected.
Does anyone
have any insight into which behavior is "correct" and whether this is a bug
or not?
It is not a bug. The formatting is done by the OS, so the results are always
OS-dependent -- since %0s is undefined, the OS can choose to interpret it any
way it wants.
Here's a slightly related question: If a single percent sign appears in a
string, not as the start of a conversion spec, is the behaviour defined? For
example, something taken from the R do_sprintf source in one of the error
messages:
"the '%*' constructed 'fmt2' exceeds maximum of %d"
There's certainly one decimal value to be displayed at the end, but is the %*
guaranteed to be interpreted literally? The R sprintf parser gets confused by
this one, but it's actually in the C code; is it a legal C format string?
Again, POSIX says the behavior is undefined in that case:
"If a conversion specification does not match one of the above forms, the behavior
is undefined. If any argument is not the correct type for the corresponding conversion
specification, the behavior is undefined."
The only reliable way to emit a percent sign is "%%". The example above is
certainly a bug.
Thanks, I'll fix it. (I think the error can't actually occur in real
code, but I'll leave the test in place.)
Duncan Murdoch
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