Why does 'Date::strptime' accept invalid strings as valid month names?

Ruby
1

Hi,

I was looking for if I can use Date::strptime method to check if a
string
can be validate as valid month or not, Thus I tested it with few
random
strings. It was meeting my expectation too.

Date::strptime(“January”,’%B’)

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

Date::strptime(“JaNuary”,’%B’)

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

Date::strptime(“JaNua”,’%B’)

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

2.0.0-p451 :005 > Date::strptime(“Foo”,’%B’)

ArgumentError: invalid date

Date::strptime(“Jan”,’%B’)

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

Date::strptime(“Janu”,’%B’)

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

Now all are going above my head.

Date::strptime(“Marche”,’%B’)

=> #<Date: 2014-03-01 ((2456718j,0s,0n),+0s,2299161j)>

Date::strptime(“Marcheee”,’%B’)
#=> #<Date: 2014-03-01 ((2456718j,0s,0n),+0s,2299161j)>
Date::strptime(“Mayil”,’%B’)

=> #<Date: 2014-05-01 ((2456779j,0s,0n),+0s,2299161j)>

Date::strptime(“Juneixyt”,’%B’)

=> #<Date: 2014-06-01 ((2456810j,0s,0n),+0s,2299161j)>

Does that mean valid English month name checking this way is not safe ?
:frowning:

–

Regards,
Arup R.

Debugging is twice as hard as writing the code in the first place.
Therefore,
if you write the code as cleverly as possible, you are, by definition,
not
smart enough to debug it.

–Brian Kernighan

2

On Monday, June 09, 2014 05:56:14 PM Jess Gabriel y Galn wrote:

So, if your string contains the name of the month, it will match, even
though it contains further characters.

Jesus.

Some more exception. How the below are valid also, as junks between the
actual
names also not making Ruby to throw error as Invalid date, as it
supposed to
do:

2.0.0-p451 :003 > Date::strptime(“Jantuary”,’%B’)
=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>
2.0.0-p451 :004 > Date::strptime(“Janxtuary”,’%B’)
=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>
2.0.0-p451 :005 >

–

Regards,
Arup R.

Debugging is twice as hard as writing the code in the first place.
Therefore,
if you write the code as cleverly as possible, you are, by definition,
not
smart enough to debug it.

–Brian Kernighan

3

On Mon, Jun 9, 2014 at 4:35 PM, Arup R.
[email protected] wrote:

=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>

Date::strptime(“Marche”,‘%B’)

=> #<Date: 2014-03-01 ((2456718j,0s,0n),+0s,2299161j)>

Date::strptime(“Marcheee”,‘%B’)
#=> #<Date: 2014-03-01 ((2456718j,0s,0n),+0s,2299161j)>
Date::strptime(“Mayil”,‘%B’)

=> #<Date: 2014-05-01 ((2456779j,0s,0n),+0s,2299161j)>

Date::strptime(“Juneixyt”,‘%B’)

=> #<Date: 2014-06-01 ((2456810j,0s,0n),+0s,2299161j)>

Does that mean valid English month name checking this way is not safe ? :frowning:

It looks like MRI is checking the words only up to the month’s name
length (check:
ruby/ext/date/date_strptime.c at a3a6da5ec51c17390a6c8c6fe733a3a59eca4a69 · ruby/ruby · GitHub)

 case 'B':
 case 'b':
 case 'h':

{
int i;

for (i = 0; i < (int)sizeof_array(month_names); i++) {
size_t l = strlen(month_names[i]);
if (strncasecmp(month_names[i], &str[si], l) == 0) {
si += l;
set_hash(“mon”, INT2FIX((i % 12) + 1));
goto matched;
}
}
fail();
}

So, if your string contains the name of the month, it will match, even
though it contains further characters.

Jesus.

4

On Monday, June 09, 2014 06:23:56 PM Jess Gabriel y Galn wrote:

So, even though January doesn’t match, Jan does, and so it is parsed.

Jesus.

Another thing to note here for Time objects. I used Time#strftim by
mistake
with %Q option and got the below output, which forced me to check the
doc
and I found it is not there. I expected some error,while invalid string
formats. But it gave me the string back.

time = Time.now
time.strftime("%Q") # => “%Q”

–

Regards,
Arup R.

Debugging is twice as hard as writing the code in the first place.
Therefore,
if you write the code as cleverly as possible, you are, by definition,
not
smart enough to debug it.

–Brian Kernighan

5

On Jun 10, 2014, at 12:05, Arup R. [email protected]
wrote:

formats*. But it gave me the string back.
From the doco:

The directives begin with a percent (%) character. Any text not listed as a
directive will be passed through to the output string.

I interpret that to mean that “%”
will pass through just like your example:

6

On Mon, Jun 9, 2014 at 5:20 PM, Arup R.
[email protected] wrote:

2.0.0-p451 :003 > Date::strptime(“Jantuary”,‘%B’)
=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>
2.0.0-p451 :004 > Date::strptime(“Janxtuary”,‘%B’)
=> #<Date: 2014-01-01 ((2456659j,0s,0n),+0s,2299161j)>
2.0.0-p451 :005 >

You can see in the link I pasted before, that it’s trying to match the
following names:

static const char *month_names[] = {
“January”, “February”, “March”, “April”,
“May”, “June”, “July”, “August”, “September”,
“October”, “November”, “December”,
“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”,
“Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”
};

So, even though January doesn’t match, Jan does, and so it is parsed.

Jesus.

7

On Tuesday, June 10, 2014 04:10:49 PM Ryan D. wrote:

From the doco:

The directives begin with a percent (%) character. Any text not listed as
a
directive will be passed through to the output string.

I interpret that to mean that “%” will
pass through just like your example:

Thank Ryan. Yes it is mentioned in the doc, and somehow I skipped that
while I
was reading the doc.

–

Regards,
Arup R.

Debugging is twice as hard as writing the code in the first place.
Therefore,
if you write the code as cleverly as possible, you are, by definition,
not
smart enough to debug it.

–Brian Kernighan