[Coco] INSTR question

[Allen Huffman]

In the examples that return 0 if matching the in the first position or "", what do they return if no match is found?

> On Feb 19, 2017, at 8:36 AM, Mathieu Bouchard <matju at artengine.ca> wrote:
> 
> 
> I searched for real and it isn't exactly that universal. Let's start with some that are consistent :
> 
> Ruby (both plain search & pattern matching) :
> "ABC".index"A"
> 0
> "ABC".index""
> 0
> /A/ =~ "ABC"
> 0
> // =~ "ABC"
> 0
> 
> Perl :
> print index("ABC","A")."\n"
> 0
> print index("ABC","")."\n"
> 0
> "ABC" =~ /A/; print "@-\n"
> 0
> "ABC" =~ //; print "@-\n"
> 0
> 
> Python :
> "ABC".index("A")
> 0
> "ABC".index("")
> 0
> re.search("A","ABC").start()
> 0
> re.search("","ABC").start()
> 0
> 
> Java :
> System.out.println("ABC".indexOf("A"));
> 0
> System.out.println("ABC".indexOf(""));
> 0
> 
> C (where this behaviour probably originated from) :
> const char *s="abc"; printf("%zd %zd\n",strstr(s,"a")-s,strstr(s,"")-s);
> 0 0
> 
> C++ STL :
> string s="abc"; printf("%zd %zd\n",s.find("a"),s.find(""));
> 0 0
> 
> Unix shells pattern matching :
> echo ABC | grep -b A
> 0:ABC
> echo ABC | grep -b ""
> 0:ABC
> 
> (the list could go on)
> 
> However, Tcl is not consistent (doesn't find empty string) :
> string first A ABC
> 0
> string first "" ABC
> -1
> 
> And also not consistent in PHP and issues a warning (wow !) :
> var_export(strpos("abc","a"));
> 0
> var_export(strpos("abc",""));
> PHP Warning:  strpos(): Empty needle in php shell code on line 1
> false
> 
> But there's an alternate consistent way in Tcl, using pattern matching :
> regexp -indices a abc x; lindex $x 0
> 0
> regexp -indices "" abc x; lindex $x 0
> 0
> 
> And in PHP too :
> preg_match("/a/","abc",$m,PREG_OFFSET_CAPTURE); var_export($m[0][1]);
> 0
> preg_match("//","abc",$m,PREG_OFFSET_CAPTURE); var_export($m[0][1]);
> 0
> 
> 
>> Le 2017-02-10 à 15:05:00, Paulo Garcia a écrit :
>> 
>> Interesting discussion. Indeed the same behaviour is found in Python and
>> Javascript:
>> 
>> NodeJS:
>> 
>>> a='ABC'
>> 'ABC'
>>> a.indexOf('A')
>> 0
>>> a.indexOf('B')
>> 1
>>> a.indexOf('C')
>> 2
>>> a.indexOf('')
>> 0
>>> 
>> 
>> Python:
>> 
>>>>> a='ABC'
>>>>> a.index('B')
>> 1
>>>>> a.index('A')
>> 0
>>>>> a.index('')
>> 0
>>>>> 
>> 
>> 
>> Paulo
>> 
>> On Fri, Feb 10, 2017 at 2:29 PM, Mathieu Bouchard <matju at artengine.ca>
>> wrote:
>> 
>>> 
>>> Nope, it's like that in probably every language that has such a search
>>> function : an empty string is found at EVERY position in the string,
>>> therefore the first match it finds is wherever the search begins. It's the
>>> normal way of doing it, because it logically fits the way N characters are
>>> searched in a string, for N=0, and the behaviour you wish would mean adding
>>> a special case for N=0 where programmers prefer to define functions so that
>>> they have the least possible number of cases.
>>> 
>>> (However, in other languages, 0 is the first position in the string,
>>> whereas "no match" is represented by another value (such as -1 or nil or
>>> error))
>>> 
>>> 
>>> Le 2017-02-09 à 15:12:00, Allen Huffman a écrit :
>>> 
>>> ...but I noticed today it finds the empty string: ""
>>>> 
>>>> PRINT INSTR("ABCDE", "")
>>>> 1
>>>> 
>>>> That seems like a bug.
>>>> A$=""
>>>> PRINT INSTR("ABCD", A$)
>>>> 1
>>>> 
>>> 
>>> ______________________________________________________________________
>>> | Mathieu BOUCHARD --- tél: 514.623.3801, 514.383.3801 --- Montréal, QC
>>> 
>>> 
>>> --
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>>> Coco at maltedmedia.com
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>>> 
>> 
>> 
>> 
>> -- 
>> --------------------------------------------
>> Paulo
>> 
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> 
> ______________________________________________________________________
> | Mathieu BOUCHARD --- tél: 514.623.3801, 514.383.3801 --- Montréal, QC
> 
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